Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Kirti Wankhede]

On 4/18/2017 8:24 AM, Peter Xu wrote:
> On Mon, Apr 17, 2017 at 03:32:20PM -0600, Alex Williamson wrote:
>> On Tue, 18 Apr 2017 01:02:12 +0530
>> Kirti Wankhede  wrote:
>>
>>> On 4/18/2017 12:49 AM, Alex Williamson wrote:
 On Tue, 18 Apr 2017 00:35:06 +0530
 Kirti Wankhede  wrote:
   
> On 4/17/2017 8:02 PM, Alex Williamson wrote:  
>> On Mon, 17 Apr 2017 14:47:54 +0800
>> Peter Xu  wrote:
>> 
>>> On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:
>>>
>>> [...]
>>>
 -static void vfio_lock_acct(struct task_struct *task, long npage)
 +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
 lock_cap)
  {
 -  struct vwork *vwork;
struct mm_struct *mm;
bool is_current;
 +  int ret;
  
if (!npage)
 -  return;
 +  return 0;
  
is_current = (task->mm == current->mm);
  
mm = is_current ? task->mm : get_task_mm(task);
if (!mm)
 -  return; /* process exited */
 +  return -ESRCH; /* process exited */
  
 -  if (down_write_trylock(>mmap_sem)) {
 -  mm->locked_vm += npage;
 -  up_write(>mmap_sem);
 -  if (!is_current)
 -  mmput(mm);
 -  return;
 -  }
 +  ret = down_write_killable(>mmap_sem);
 +  if (!ret) {
 +  if (npage < 0 || lock_cap) {  
>>>
>>> Nit: maybe we can avoid passing in lock_cap in all the callers of
>>> vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
>>> IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
>>> need to pass in "false" any time when doing unpins.
>>
>> Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
>> since it tests whether the user is exceeding their locked memory
>> limit.  The other callers could certainly get away with
>> vfio_lock_acct() testing the capability itself but that would add a
>> redundant call for the most common user.  I'm not a big fan of passing
>> a lock_cap bool either, but it seemed the best fix for now.  The
>> cleanest alternative I can up with is this (untested):
>> 
>
> In my opinion, passing 'bool lock_cap' looks much clean and simple.
>
> Reviewed-by: Kirti Wankhede   

 Well shoot, I was just starting to warm up to the bool*.  I like that
 we're not presuming the polarity for the callers we expect to be
 removing pages and I generally just dislike passing fixed bool
 parameters to change the function behavior.  I've cleaned it up a bit
 further and was starting to do some testing on this which I'd propose
 for v5.  Does it change your opinion?  
>>>
>>> If passing fixed bool parameter is the concern then I would lean towards
>>> Peter's suggestion. vfio_pin_pages_remote() will check lock capability
>>> outside vfio_lock_acct() and again in vfio_lock_acct(). At other places,
>>> it will be takes care within vfio_lock_acct()
>>
>> Sorry, I don't see that as a viable option.  Testing for CAP_IPC_LOCK in
>> both vfio_pin_pages_remote() and vfio_lock_acct() results in over a
>> 10% performance hit on the mapping path with a custom micro-benchmark.
>> In fact, it suggests we should probably pass that from even higher in
>> the call stack.  Thanks,
> 
> Sorry I wasn't aware of such a performance degradation with such a
> change. Then I would be perfectly fine with either current patch, or
> the new one you proposed (with bool *). Thanks,
> 

Sorry, even I wasn't aware of.
Looking at v5 version now.

Thanks,
Kirti

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Kirti Wankhede]

On 4/18/2017 8:24 AM, Peter Xu wrote:
> On Mon, Apr 17, 2017 at 03:32:20PM -0600, Alex Williamson wrote:
>> On Tue, 18 Apr 2017 01:02:12 +0530
>> Kirti Wankhede  wrote:
>>
>>> On 4/18/2017 12:49 AM, Alex Williamson wrote:
 On Tue, 18 Apr 2017 00:35:06 +0530
 Kirti Wankhede  wrote:
   
> On 4/17/2017 8:02 PM, Alex Williamson wrote:  
>> On Mon, 17 Apr 2017 14:47:54 +0800
>> Peter Xu  wrote:
>> 
>>> On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:
>>>
>>> [...]
>>>
 -static void vfio_lock_acct(struct task_struct *task, long npage)
 +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
 lock_cap)
  {
 -  struct vwork *vwork;
struct mm_struct *mm;
bool is_current;
 +  int ret;
  
if (!npage)
 -  return;
 +  return 0;
  
is_current = (task->mm == current->mm);
  
mm = is_current ? task->mm : get_task_mm(task);
if (!mm)
 -  return; /* process exited */
 +  return -ESRCH; /* process exited */
  
 -  if (down_write_trylock(>mmap_sem)) {
 -  mm->locked_vm += npage;
 -  up_write(>mmap_sem);
 -  if (!is_current)
 -  mmput(mm);
 -  return;
 -  }
 +  ret = down_write_killable(>mmap_sem);
 +  if (!ret) {
 +  if (npage < 0 || lock_cap) {  
>>>
>>> Nit: maybe we can avoid passing in lock_cap in all the callers of
>>> vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
>>> IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
>>> need to pass in "false" any time when doing unpins.
>>
>> Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
>> since it tests whether the user is exceeding their locked memory
>> limit.  The other callers could certainly get away with
>> vfio_lock_acct() testing the capability itself but that would add a
>> redundant call for the most common user.  I'm not a big fan of passing
>> a lock_cap bool either, but it seemed the best fix for now.  The
>> cleanest alternative I can up with is this (untested):
>> 
>
> In my opinion, passing 'bool lock_cap' looks much clean and simple.
>
> Reviewed-by: Kirti Wankhede   

 Well shoot, I was just starting to warm up to the bool*.  I like that
 we're not presuming the polarity for the callers we expect to be
 removing pages and I generally just dislike passing fixed bool
 parameters to change the function behavior.  I've cleaned it up a bit
 further and was starting to do some testing on this which I'd propose
 for v5.  Does it change your opinion?  
>>>
>>> If passing fixed bool parameter is the concern then I would lean towards
>>> Peter's suggestion. vfio_pin_pages_remote() will check lock capability
>>> outside vfio_lock_acct() and again in vfio_lock_acct(). At other places,
>>> it will be takes care within vfio_lock_acct()
>>
>> Sorry, I don't see that as a viable option.  Testing for CAP_IPC_LOCK in
>> both vfio_pin_pages_remote() and vfio_lock_acct() results in over a
>> 10% performance hit on the mapping path with a custom micro-benchmark.
>> In fact, it suggests we should probably pass that from even higher in
>> the call stack.  Thanks,
> 
> Sorry I wasn't aware of such a performance degradation with such a
> change. Then I would be perfectly fine with either current patch, or
> the new one you proposed (with bool *). Thanks,
> 

Sorry, even I wasn't aware of.
Looking at v5 version now.

Thanks,
Kirti

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Peter Xu]

On Mon, Apr 17, 2017 at 03:32:20PM -0600, Alex Williamson wrote:
> On Tue, 18 Apr 2017 01:02:12 +0530
> Kirti Wankhede  wrote:
> 
> > On 4/18/2017 12:49 AM, Alex Williamson wrote:
> > > On Tue, 18 Apr 2017 00:35:06 +0530
> > > Kirti Wankhede  wrote:
> > >   
> > >> On 4/17/2017 8:02 PM, Alex Williamson wrote:  
> > >>> On Mon, 17 Apr 2017 14:47:54 +0800
> > >>> Peter Xu  wrote:
> > >>> 
> >  On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:
> > 
> >  [...]
> > 
> > > -static void vfio_lock_acct(struct task_struct *task, long npage)
> > > +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> > > lock_cap)
> > >  {
> > > - struct vwork *vwork;
> > >   struct mm_struct *mm;
> > >   bool is_current;
> > > + int ret;
> > >  
> > >   if (!npage)
> > > - return;
> > > + return 0;
> > >  
> > >   is_current = (task->mm == current->mm);
> > >  
> > >   mm = is_current ? task->mm : get_task_mm(task);
> > >   if (!mm)
> > > - return; /* process exited */
> > > + return -ESRCH; /* process exited */
> > >  
> > > - if (down_write_trylock(>mmap_sem)) {
> > > - mm->locked_vm += npage;
> > > - up_write(>mmap_sem);
> > > - if (!is_current)
> > > - mmput(mm);
> > > - return;
> > > - }
> > > + ret = down_write_killable(>mmap_sem);
> > > + if (!ret) {
> > > + if (npage < 0 || lock_cap) {  
> > 
> >  Nit: maybe we can avoid passing in lock_cap in all the callers of
> >  vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
> >  IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
> >  need to pass in "false" any time when doing unpins.
> > >>>
> > >>> Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
> > >>> since it tests whether the user is exceeding their locked memory
> > >>> limit.  The other callers could certainly get away with
> > >>> vfio_lock_acct() testing the capability itself but that would add a
> > >>> redundant call for the most common user.  I'm not a big fan of passing
> > >>> a lock_cap bool either, but it seemed the best fix for now.  The
> > >>> cleanest alternative I can up with is this (untested):
> > >>> 
> > >>
> > >> In my opinion, passing 'bool lock_cap' looks much clean and simple.
> > >>
> > >> Reviewed-by: Kirti Wankhede   
> > > 
> > > Well shoot, I was just starting to warm up to the bool*.  I like that
> > > we're not presuming the polarity for the callers we expect to be
> > > removing pages and I generally just dislike passing fixed bool
> > > parameters to change the function behavior.  I've cleaned it up a bit
> > > further and was starting to do some testing on this which I'd propose
> > > for v5.  Does it change your opinion?  
> > 
> > If passing fixed bool parameter is the concern then I would lean towards
> > Peter's suggestion. vfio_pin_pages_remote() will check lock capability
> > outside vfio_lock_acct() and again in vfio_lock_acct(). At other places,
> > it will be takes care within vfio_lock_acct()
> 
> Sorry, I don't see that as a viable option.  Testing for CAP_IPC_LOCK in
> both vfio_pin_pages_remote() and vfio_lock_acct() results in over a
> 10% performance hit on the mapping path with a custom micro-benchmark.
> In fact, it suggests we should probably pass that from even higher in
> the call stack.  Thanks,

Sorry I wasn't aware of such a performance degradation with such a
change. Then I would be perfectly fine with either current patch, or
the new one you proposed (with bool *). Thanks,

-- 
Peter Xu

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Peter Xu]

On Mon, Apr 17, 2017 at 03:32:20PM -0600, Alex Williamson wrote:
> On Tue, 18 Apr 2017 01:02:12 +0530
> Kirti Wankhede  wrote:
> 
> > On 4/18/2017 12:49 AM, Alex Williamson wrote:
> > > On Tue, 18 Apr 2017 00:35:06 +0530
> > > Kirti Wankhede  wrote:
> > >   
> > >> On 4/17/2017 8:02 PM, Alex Williamson wrote:  
> > >>> On Mon, 17 Apr 2017 14:47:54 +0800
> > >>> Peter Xu  wrote:
> > >>> 
> >  On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:
> > 
> >  [...]
> > 
> > > -static void vfio_lock_acct(struct task_struct *task, long npage)
> > > +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> > > lock_cap)
> > >  {
> > > - struct vwork *vwork;
> > >   struct mm_struct *mm;
> > >   bool is_current;
> > > + int ret;
> > >  
> > >   if (!npage)
> > > - return;
> > > + return 0;
> > >  
> > >   is_current = (task->mm == current->mm);
> > >  
> > >   mm = is_current ? task->mm : get_task_mm(task);
> > >   if (!mm)
> > > - return; /* process exited */
> > > + return -ESRCH; /* process exited */
> > >  
> > > - if (down_write_trylock(>mmap_sem)) {
> > > - mm->locked_vm += npage;
> > > - up_write(>mmap_sem);
> > > - if (!is_current)
> > > - mmput(mm);
> > > - return;
> > > - }
> > > + ret = down_write_killable(>mmap_sem);
> > > + if (!ret) {
> > > + if (npage < 0 || lock_cap) {  
> > 
> >  Nit: maybe we can avoid passing in lock_cap in all the callers of
> >  vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
> >  IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
> >  need to pass in "false" any time when doing unpins.
> > >>>
> > >>> Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
> > >>> since it tests whether the user is exceeding their locked memory
> > >>> limit.  The other callers could certainly get away with
> > >>> vfio_lock_acct() testing the capability itself but that would add a
> > >>> redundant call for the most common user.  I'm not a big fan of passing
> > >>> a lock_cap bool either, but it seemed the best fix for now.  The
> > >>> cleanest alternative I can up with is this (untested):
> > >>> 
> > >>
> > >> In my opinion, passing 'bool lock_cap' looks much clean and simple.
> > >>
> > >> Reviewed-by: Kirti Wankhede   
> > > 
> > > Well shoot, I was just starting to warm up to the bool*.  I like that
> > > we're not presuming the polarity for the callers we expect to be
> > > removing pages and I generally just dislike passing fixed bool
> > > parameters to change the function behavior.  I've cleaned it up a bit
> > > further and was starting to do some testing on this which I'd propose
> > > for v5.  Does it change your opinion?  
> > 
> > If passing fixed bool parameter is the concern then I would lean towards
> > Peter's suggestion. vfio_pin_pages_remote() will check lock capability
> > outside vfio_lock_acct() and again in vfio_lock_acct(). At other places,
> > it will be takes care within vfio_lock_acct()
> 
> Sorry, I don't see that as a viable option.  Testing for CAP_IPC_LOCK in
> both vfio_pin_pages_remote() and vfio_lock_acct() results in over a
> 10% performance hit on the mapping path with a custom micro-benchmark.
> In fact, it suggests we should probably pass that from even higher in
> the call stack.  Thanks,

Sorry I wasn't aware of such a performance degradation with such a
change. Then I would be perfectly fine with either current patch, or
the new one you proposed (with bool *). Thanks,

-- 
Peter Xu

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Alex Williamson]

On Tue, 18 Apr 2017 01:02:12 +0530
Kirti Wankhede  wrote:

> On 4/18/2017 12:49 AM, Alex Williamson wrote:
> > On Tue, 18 Apr 2017 00:35:06 +0530
> > Kirti Wankhede  wrote:
> >   
> >> On 4/17/2017 8:02 PM, Alex Williamson wrote:  
> >>> On Mon, 17 Apr 2017 14:47:54 +0800
> >>> Peter Xu  wrote:
> >>> 
>  On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:
> 
>  [...]
> 
> > -static void vfio_lock_acct(struct task_struct *task, long npage)
> > +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> > lock_cap)
> >  {
> > -   struct vwork *vwork;
> > struct mm_struct *mm;
> > bool is_current;
> > +   int ret;
> >  
> > if (!npage)
> > -   return;
> > +   return 0;
> >  
> > is_current = (task->mm == current->mm);
> >  
> > mm = is_current ? task->mm : get_task_mm(task);
> > if (!mm)
> > -   return; /* process exited */
> > +   return -ESRCH; /* process exited */
> >  
> > -   if (down_write_trylock(>mmap_sem)) {
> > -   mm->locked_vm += npage;
> > -   up_write(>mmap_sem);
> > -   if (!is_current)
> > -   mmput(mm);
> > -   return;
> > -   }
> > +   ret = down_write_killable(>mmap_sem);
> > +   if (!ret) {
> > +   if (npage < 0 || lock_cap) {  
> 
>  Nit: maybe we can avoid passing in lock_cap in all the callers of
>  vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
>  IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
>  need to pass in "false" any time when doing unpins.
> >>>
> >>> Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
> >>> since it tests whether the user is exceeding their locked memory
> >>> limit.  The other callers could certainly get away with
> >>> vfio_lock_acct() testing the capability itself but that would add a
> >>> redundant call for the most common user.  I'm not a big fan of passing
> >>> a lock_cap bool either, but it seemed the best fix for now.  The
> >>> cleanest alternative I can up with is this (untested):
> >>> 
> >>
> >> In my opinion, passing 'bool lock_cap' looks much clean and simple.
> >>
> >> Reviewed-by: Kirti Wankhede   
> > 
> > Well shoot, I was just starting to warm up to the bool*.  I like that
> > we're not presuming the polarity for the callers we expect to be
> > removing pages and I generally just dislike passing fixed bool
> > parameters to change the function behavior.  I've cleaned it up a bit
> > further and was starting to do some testing on this which I'd propose
> > for v5.  Does it change your opinion?  
> 
> If passing fixed bool parameter is the concern then I would lean towards
> Peter's suggestion. vfio_pin_pages_remote() will check lock capability
> outside vfio_lock_acct() and again in vfio_lock_acct(). At other places,
> it will be takes care within vfio_lock_acct()

Sorry, I don't see that as a viable option.  Testing for CAP_IPC_LOCK in
both vfio_pin_pages_remote() and vfio_lock_acct() results in over a
10% performance hit on the mapping path with a custom micro-benchmark.
In fact, it suggests we should probably pass that from even higher in
the call stack.  Thanks,

Alex

> > 
> > commit cd61c5f507d614ac14b75b0a548c8738deff88ea
> > Author: Alex Williamson 
> > Date:   Thu Apr 13 14:10:15 2017 -0600
> > 
> > vfio/type1: Remove locked page accounting workqueue
> > 
> > If the mmap_sem is contented then the vfio type1 IOMMU backend will
> > defer locked page accounting updates to a workqueue task.  This has a
> > few problems and depending on which side the user tries to play, they
> > might be over-penalized for unmaps that haven't yet been accounted or
> > race the workqueue to enter more mappings than they're allowed.  The
> > original intent of this workqueue mechanism seems to be focused on
> > reducing latency through the ioctl, but we cannot do so at the cost
> > of correctness.  Remove this workqueue mechanism and update the
> > callers to allow for failure.  We can also now recheck the limit under
> > write lock to make sure we don't exceed it.
> > 
> > vfio_pin_pages_remote() also now necessarily includes an unwind path
> > which we can jump to directly if the consecutive page pinning finds
> > that we're exceeding the user's memory limits.  This avoids the
> > current lazy approach which does accounting and mapping up to the
> > fault, only to return an error on the next iteration to unwind the
> > entire vfio_dma.
> > 
> > Cc: sta...@vger.kernel.org
> > Signed-off-by: Alex 

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Alex Williamson]

On Tue, 18 Apr 2017 01:02:12 +0530
Kirti Wankhede  wrote:

> On 4/18/2017 12:49 AM, Alex Williamson wrote:
> > On Tue, 18 Apr 2017 00:35:06 +0530
> > Kirti Wankhede  wrote:
> >   
> >> On 4/17/2017 8:02 PM, Alex Williamson wrote:  
> >>> On Mon, 17 Apr 2017 14:47:54 +0800
> >>> Peter Xu  wrote:
> >>> 
>  On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:
> 
>  [...]
> 
> > -static void vfio_lock_acct(struct task_struct *task, long npage)
> > +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> > lock_cap)
> >  {
> > -   struct vwork *vwork;
> > struct mm_struct *mm;
> > bool is_current;
> > +   int ret;
> >  
> > if (!npage)
> > -   return;
> > +   return 0;
> >  
> > is_current = (task->mm == current->mm);
> >  
> > mm = is_current ? task->mm : get_task_mm(task);
> > if (!mm)
> > -   return; /* process exited */
> > +   return -ESRCH; /* process exited */
> >  
> > -   if (down_write_trylock(>mmap_sem)) {
> > -   mm->locked_vm += npage;
> > -   up_write(>mmap_sem);
> > -   if (!is_current)
> > -   mmput(mm);
> > -   return;
> > -   }
> > +   ret = down_write_killable(>mmap_sem);
> > +   if (!ret) {
> > +   if (npage < 0 || lock_cap) {  
> 
>  Nit: maybe we can avoid passing in lock_cap in all the callers of
>  vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
>  IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
>  need to pass in "false" any time when doing unpins.
> >>>
> >>> Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
> >>> since it tests whether the user is exceeding their locked memory
> >>> limit.  The other callers could certainly get away with
> >>> vfio_lock_acct() testing the capability itself but that would add a
> >>> redundant call for the most common user.  I'm not a big fan of passing
> >>> a lock_cap bool either, but it seemed the best fix for now.  The
> >>> cleanest alternative I can up with is this (untested):
> >>> 
> >>
> >> In my opinion, passing 'bool lock_cap' looks much clean and simple.
> >>
> >> Reviewed-by: Kirti Wankhede   
> > 
> > Well shoot, I was just starting to warm up to the bool*.  I like that
> > we're not presuming the polarity for the callers we expect to be
> > removing pages and I generally just dislike passing fixed bool
> > parameters to change the function behavior.  I've cleaned it up a bit
> > further and was starting to do some testing on this which I'd propose
> > for v5.  Does it change your opinion?  
> 
> If passing fixed bool parameter is the concern then I would lean towards
> Peter's suggestion. vfio_pin_pages_remote() will check lock capability
> outside vfio_lock_acct() and again in vfio_lock_acct(). At other places,
> it will be takes care within vfio_lock_acct()

Sorry, I don't see that as a viable option.  Testing for CAP_IPC_LOCK in
both vfio_pin_pages_remote() and vfio_lock_acct() results in over a
10% performance hit on the mapping path with a custom micro-benchmark.
In fact, it suggests we should probably pass that from even higher in
the call stack.  Thanks,

Alex

> > 
> > commit cd61c5f507d614ac14b75b0a548c8738deff88ea
> > Author: Alex Williamson 
> > Date:   Thu Apr 13 14:10:15 2017 -0600
> > 
> > vfio/type1: Remove locked page accounting workqueue
> > 
> > If the mmap_sem is contented then the vfio type1 IOMMU backend will
> > defer locked page accounting updates to a workqueue task.  This has a
> > few problems and depending on which side the user tries to play, they
> > might be over-penalized for unmaps that haven't yet been accounted or
> > race the workqueue to enter more mappings than they're allowed.  The
> > original intent of this workqueue mechanism seems to be focused on
> > reducing latency through the ioctl, but we cannot do so at the cost
> > of correctness.  Remove this workqueue mechanism and update the
> > callers to allow for failure.  We can also now recheck the limit under
> > write lock to make sure we don't exceed it.
> > 
> > vfio_pin_pages_remote() also now necessarily includes an unwind path
> > which we can jump to directly if the consecutive page pinning finds
> > that we're exceeding the user's memory limits.  This avoids the
> > current lazy approach which does accounting and mapping up to the
> > fault, only to return an error on the next iteration to unwind the
> > entire vfio_dma.
> > 
> > Cc: sta...@vger.kernel.org
> > Signed-off-by: Alex Williamson 
> > 
> > diff --git a/drivers/vfio/vfio_iommu_type1.c 
> > b/drivers/vfio/vfio_iommu_type1.c
> > index 

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Kirti Wankhede]

On 4/18/2017 12:49 AM, Alex Williamson wrote:
> On Tue, 18 Apr 2017 00:35:06 +0530
> Kirti Wankhede  wrote:
> 
>> On 4/17/2017 8:02 PM, Alex Williamson wrote:
>>> On Mon, 17 Apr 2017 14:47:54 +0800
>>> Peter Xu  wrote:
>>>   
 On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:

 [...]
  
> -static void vfio_lock_acct(struct task_struct *task, long npage)
> +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> lock_cap)
>  {
> - struct vwork *vwork;
>   struct mm_struct *mm;
>   bool is_current;
> + int ret;
>  
>   if (!npage)
> - return;
> + return 0;
>  
>   is_current = (task->mm == current->mm);
>  
>   mm = is_current ? task->mm : get_task_mm(task);
>   if (!mm)
> - return; /* process exited */
> + return -ESRCH; /* process exited */
>  
> - if (down_write_trylock(>mmap_sem)) {
> - mm->locked_vm += npage;
> - up_write(>mmap_sem);
> - if (!is_current)
> - mmput(mm);
> - return;
> - }
> + ret = down_write_killable(>mmap_sem);
> + if (!ret) {
> + if (npage < 0 || lock_cap) {

 Nit: maybe we can avoid passing in lock_cap in all the callers of
 vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
 IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
 need to pass in "false" any time when doing unpins.  
>>>
>>> Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
>>> since it tests whether the user is exceeding their locked memory
>>> limit.  The other callers could certainly get away with
>>> vfio_lock_acct() testing the capability itself but that would add a
>>> redundant call for the most common user.  I'm not a big fan of passing
>>> a lock_cap bool either, but it seemed the best fix for now.  The
>>> cleanest alternative I can up with is this (untested):
>>>   
>>
>> In my opinion, passing 'bool lock_cap' looks much clean and simple.
>>
>> Reviewed-by: Kirti Wankhede 
> 
> Well shoot, I was just starting to warm up to the bool*.  I like that
> we're not presuming the polarity for the callers we expect to be
> removing pages and I generally just dislike passing fixed bool
> parameters to change the function behavior.  I've cleaned it up a bit
> further and was starting to do some testing on this which I'd propose
> for v5.  Does it change your opinion?

If passing fixed bool parameter is the concern then I would lean towards
Peter's suggestion. vfio_pin_pages_remote() will check lock capability
outside vfio_lock_acct() and again in vfio_lock_acct(). At other places,
it will be takes care within vfio_lock_acct()

Thanks,
Kirti

> 
> commit cd61c5f507d614ac14b75b0a548c8738deff88ea
> Author: Alex Williamson 
> Date:   Thu Apr 13 14:10:15 2017 -0600
> 
> vfio/type1: Remove locked page accounting workqueue
> 
> If the mmap_sem is contented then the vfio type1 IOMMU backend will
> defer locked page accounting updates to a workqueue task.  This has a
> few problems and depending on which side the user tries to play, they
> might be over-penalized for unmaps that haven't yet been accounted or
> race the workqueue to enter more mappings than they're allowed.  The
> original intent of this workqueue mechanism seems to be focused on
> reducing latency through the ioctl, but we cannot do so at the cost
> of correctness.  Remove this workqueue mechanism and update the
> callers to allow for failure.  We can also now recheck the limit under
> write lock to make sure we don't exceed it.
> 
> vfio_pin_pages_remote() also now necessarily includes an unwind path
> which we can jump to directly if the consecutive page pinning finds
> that we're exceeding the user's memory limits.  This avoids the
> current lazy approach which does accounting and mapping up to the
> fault, only to return an error on the next iteration to unwind the
> entire vfio_dma.
> 
> Cc: sta...@vger.kernel.org
> Signed-off-by: Alex Williamson 
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 32d2633092a3..a8a079ba9477 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -246,69 +246,46 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, 
> struct vfio_pfn *vpfn)
>   return ret;
>  }
>  
> -struct vwork {
> - struct mm_struct*mm;
> - longnpage;
> - struct work_struct  work;
> -};
> -
> -/* delayed decrement/increment for locked_vm */
> -static void vfio_lock_acct_bg(struct work_struct *work)
> -{
> - struct vwork *vwork = container_of(work, struct vwork, work);
> - struct 

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Kirti Wankhede]

On 4/18/2017 12:49 AM, Alex Williamson wrote:
> On Tue, 18 Apr 2017 00:35:06 +0530
> Kirti Wankhede  wrote:
> 
>> On 4/17/2017 8:02 PM, Alex Williamson wrote:
>>> On Mon, 17 Apr 2017 14:47:54 +0800
>>> Peter Xu  wrote:
>>>   
 On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:

 [...]
  
> -static void vfio_lock_acct(struct task_struct *task, long npage)
> +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> lock_cap)
>  {
> - struct vwork *vwork;
>   struct mm_struct *mm;
>   bool is_current;
> + int ret;
>  
>   if (!npage)
> - return;
> + return 0;
>  
>   is_current = (task->mm == current->mm);
>  
>   mm = is_current ? task->mm : get_task_mm(task);
>   if (!mm)
> - return; /* process exited */
> + return -ESRCH; /* process exited */
>  
> - if (down_write_trylock(>mmap_sem)) {
> - mm->locked_vm += npage;
> - up_write(>mmap_sem);
> - if (!is_current)
> - mmput(mm);
> - return;
> - }
> + ret = down_write_killable(>mmap_sem);
> + if (!ret) {
> + if (npage < 0 || lock_cap) {

 Nit: maybe we can avoid passing in lock_cap in all the callers of
 vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
 IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
 need to pass in "false" any time when doing unpins.  
>>>
>>> Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
>>> since it tests whether the user is exceeding their locked memory
>>> limit.  The other callers could certainly get away with
>>> vfio_lock_acct() testing the capability itself but that would add a
>>> redundant call for the most common user.  I'm not a big fan of passing
>>> a lock_cap bool either, but it seemed the best fix for now.  The
>>> cleanest alternative I can up with is this (untested):
>>>   
>>
>> In my opinion, passing 'bool lock_cap' looks much clean and simple.
>>
>> Reviewed-by: Kirti Wankhede 
> 
> Well shoot, I was just starting to warm up to the bool*.  I like that
> we're not presuming the polarity for the callers we expect to be
> removing pages and I generally just dislike passing fixed bool
> parameters to change the function behavior.  I've cleaned it up a bit
> further and was starting to do some testing on this which I'd propose
> for v5.  Does it change your opinion?

If passing fixed bool parameter is the concern then I would lean towards
Peter's suggestion. vfio_pin_pages_remote() will check lock capability
outside vfio_lock_acct() and again in vfio_lock_acct(). At other places,
it will be takes care within vfio_lock_acct()

Thanks,
Kirti

> 
> commit cd61c5f507d614ac14b75b0a548c8738deff88ea
> Author: Alex Williamson 
> Date:   Thu Apr 13 14:10:15 2017 -0600
> 
> vfio/type1: Remove locked page accounting workqueue
> 
> If the mmap_sem is contented then the vfio type1 IOMMU backend will
> defer locked page accounting updates to a workqueue task.  This has a
> few problems and depending on which side the user tries to play, they
> might be over-penalized for unmaps that haven't yet been accounted or
> race the workqueue to enter more mappings than they're allowed.  The
> original intent of this workqueue mechanism seems to be focused on
> reducing latency through the ioctl, but we cannot do so at the cost
> of correctness.  Remove this workqueue mechanism and update the
> callers to allow for failure.  We can also now recheck the limit under
> write lock to make sure we don't exceed it.
> 
> vfio_pin_pages_remote() also now necessarily includes an unwind path
> which we can jump to directly if the consecutive page pinning finds
> that we're exceeding the user's memory limits.  This avoids the
> current lazy approach which does accounting and mapping up to the
> fault, only to return an error on the next iteration to unwind the
> entire vfio_dma.
> 
> Cc: sta...@vger.kernel.org
> Signed-off-by: Alex Williamson 
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 32d2633092a3..a8a079ba9477 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -246,69 +246,46 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, 
> struct vfio_pfn *vpfn)
>   return ret;
>  }
>  
> -struct vwork {
> - struct mm_struct*mm;
> - longnpage;
> - struct work_struct  work;
> -};
> -
> -/* delayed decrement/increment for locked_vm */
> -static void vfio_lock_acct_bg(struct work_struct *work)
> -{
> - struct vwork *vwork = container_of(work, struct vwork, work);
> - struct mm_struct *mm;
> -
> - mm = vwork->mm;
> - down_write(>mmap_sem);
> - mm->locked_vm += vwork->npage;
> - 

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Alex Williamson]

On Tue, 18 Apr 2017 00:35:06 +0530
Kirti Wankhede  wrote:

> On 4/17/2017 8:02 PM, Alex Williamson wrote:
> > On Mon, 17 Apr 2017 14:47:54 +0800
> > Peter Xu  wrote:
> >   
> >> On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:
> >>
> >> [...]
> >>  
> >>> -static void vfio_lock_acct(struct task_struct *task, long npage)
> >>> +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> >>> lock_cap)
> >>>  {
> >>> - struct vwork *vwork;
> >>>   struct mm_struct *mm;
> >>>   bool is_current;
> >>> + int ret;
> >>>  
> >>>   if (!npage)
> >>> - return;
> >>> + return 0;
> >>>  
> >>>   is_current = (task->mm == current->mm);
> >>>  
> >>>   mm = is_current ? task->mm : get_task_mm(task);
> >>>   if (!mm)
> >>> - return; /* process exited */
> >>> + return -ESRCH; /* process exited */
> >>>  
> >>> - if (down_write_trylock(>mmap_sem)) {
> >>> - mm->locked_vm += npage;
> >>> - up_write(>mmap_sem);
> >>> - if (!is_current)
> >>> - mmput(mm);
> >>> - return;
> >>> - }
> >>> + ret = down_write_killable(>mmap_sem);
> >>> + if (!ret) {
> >>> + if (npage < 0 || lock_cap) {
> >>
> >> Nit: maybe we can avoid passing in lock_cap in all the callers of
> >> vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
> >> IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
> >> need to pass in "false" any time when doing unpins.  
> > 
> > Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
> > since it tests whether the user is exceeding their locked memory
> > limit.  The other callers could certainly get away with
> > vfio_lock_acct() testing the capability itself but that would add a
> > redundant call for the most common user.  I'm not a big fan of passing
> > a lock_cap bool either, but it seemed the best fix for now.  The
> > cleanest alternative I can up with is this (untested):
> >   
> 
> In my opinion, passing 'bool lock_cap' looks much clean and simple.
> 
> Reviewed-by: Kirti Wankhede 

Well shoot, I was just starting to warm up to the bool*.  I like that
we're not presuming the polarity for the callers we expect to be
removing pages and I generally just dislike passing fixed bool
parameters to change the function behavior.  I've cleaned it up a bit
further and was starting to do some testing on this which I'd propose
for v5.  Does it change your opinion?

commit cd61c5f507d614ac14b75b0a548c8738deff88ea
Author: Alex Williamson 
Date:   Thu Apr 13 14:10:15 2017 -0600

vfio/type1: Remove locked page accounting workqueue

If the mmap_sem is contented then the vfio type1 IOMMU backend will
defer locked page accounting updates to a workqueue task.  This has a
few problems and depending on which side the user tries to play, they
might be over-penalized for unmaps that haven't yet been accounted or
race the workqueue to enter more mappings than they're allowed.  The
original intent of this workqueue mechanism seems to be focused on
reducing latency through the ioctl, but we cannot do so at the cost
of correctness.  Remove this workqueue mechanism and update the
callers to allow for failure.  We can also now recheck the limit under
write lock to make sure we don't exceed it.

vfio_pin_pages_remote() also now necessarily includes an unwind path
which we can jump to directly if the consecutive page pinning finds
that we're exceeding the user's memory limits.  This avoids the
current lazy approach which does accounting and mapping up to the
fault, only to return an error on the next iteration to unwind the
entire vfio_dma.

Cc: sta...@vger.kernel.org
Signed-off-by: Alex Williamson 

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 32d2633092a3..a8a079ba9477 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -246,69 +246,46 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, 
struct vfio_pfn *vpfn)
return ret;
 }
 
-struct vwork {
-   struct mm_struct*mm;
-   longnpage;
-   struct work_struct  work;
-};
-
-/* delayed decrement/increment for locked_vm */
-static void vfio_lock_acct_bg(struct work_struct *work)
-{
-   struct vwork *vwork = container_of(work, struct vwork, work);
-   struct mm_struct *mm;
-
-   mm = vwork->mm;
-   down_write(>mmap_sem);
-   mm->locked_vm += vwork->npage;
-   up_write(>mmap_sem);
-   mmput(mm);
-   kfree(vwork);
-}
-
-static void vfio_lock_acct(struct task_struct *task, long npage)
+static int vfio_lock_acct(struct task_struct *task, long npage, bool *lock_cap)
 {
-   struct vwork *vwork;
struct mm_struct *mm;
bool is_current;
+   int ret;
 
   

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Alex Williamson]

On Tue, 18 Apr 2017 00:35:06 +0530
Kirti Wankhede  wrote:

> On 4/17/2017 8:02 PM, Alex Williamson wrote:
> > On Mon, 17 Apr 2017 14:47:54 +0800
> > Peter Xu  wrote:
> >   
> >> On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:
> >>
> >> [...]
> >>  
> >>> -static void vfio_lock_acct(struct task_struct *task, long npage)
> >>> +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> >>> lock_cap)
> >>>  {
> >>> - struct vwork *vwork;
> >>>   struct mm_struct *mm;
> >>>   bool is_current;
> >>> + int ret;
> >>>  
> >>>   if (!npage)
> >>> - return;
> >>> + return 0;
> >>>  
> >>>   is_current = (task->mm == current->mm);
> >>>  
> >>>   mm = is_current ? task->mm : get_task_mm(task);
> >>>   if (!mm)
> >>> - return; /* process exited */
> >>> + return -ESRCH; /* process exited */
> >>>  
> >>> - if (down_write_trylock(>mmap_sem)) {
> >>> - mm->locked_vm += npage;
> >>> - up_write(>mmap_sem);
> >>> - if (!is_current)
> >>> - mmput(mm);
> >>> - return;
> >>> - }
> >>> + ret = down_write_killable(>mmap_sem);
> >>> + if (!ret) {
> >>> + if (npage < 0 || lock_cap) {
> >>
> >> Nit: maybe we can avoid passing in lock_cap in all the callers of
> >> vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
> >> IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
> >> need to pass in "false" any time when doing unpins.  
> > 
> > Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
> > since it tests whether the user is exceeding their locked memory
> > limit.  The other callers could certainly get away with
> > vfio_lock_acct() testing the capability itself but that would add a
> > redundant call for the most common user.  I'm not a big fan of passing
> > a lock_cap bool either, but it seemed the best fix for now.  The
> > cleanest alternative I can up with is this (untested):
> >   
> 
> In my opinion, passing 'bool lock_cap' looks much clean and simple.
> 
> Reviewed-by: Kirti Wankhede 

Well shoot, I was just starting to warm up to the bool*.  I like that
we're not presuming the polarity for the callers we expect to be
removing pages and I generally just dislike passing fixed bool
parameters to change the function behavior.  I've cleaned it up a bit
further and was starting to do some testing on this which I'd propose
for v5.  Does it change your opinion?

commit cd61c5f507d614ac14b75b0a548c8738deff88ea
Author: Alex Williamson 
Date:   Thu Apr 13 14:10:15 2017 -0600

vfio/type1: Remove locked page accounting workqueue

If the mmap_sem is contented then the vfio type1 IOMMU backend will
defer locked page accounting updates to a workqueue task.  This has a
few problems and depending on which side the user tries to play, they
might be over-penalized for unmaps that haven't yet been accounted or
race the workqueue to enter more mappings than they're allowed.  The
original intent of this workqueue mechanism seems to be focused on
reducing latency through the ioctl, but we cannot do so at the cost
of correctness.  Remove this workqueue mechanism and update the
callers to allow for failure.  We can also now recheck the limit under
write lock to make sure we don't exceed it.

vfio_pin_pages_remote() also now necessarily includes an unwind path
which we can jump to directly if the consecutive page pinning finds
that we're exceeding the user's memory limits.  This avoids the
current lazy approach which does accounting and mapping up to the
fault, only to return an error on the next iteration to unwind the
entire vfio_dma.

Cc: sta...@vger.kernel.org
Signed-off-by: Alex Williamson 

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 32d2633092a3..a8a079ba9477 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -246,69 +246,46 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, 
struct vfio_pfn *vpfn)
return ret;
 }
 
-struct vwork {
-   struct mm_struct*mm;
-   longnpage;
-   struct work_struct  work;
-};
-
-/* delayed decrement/increment for locked_vm */
-static void vfio_lock_acct_bg(struct work_struct *work)
-{
-   struct vwork *vwork = container_of(work, struct vwork, work);
-   struct mm_struct *mm;
-
-   mm = vwork->mm;
-   down_write(>mmap_sem);
-   mm->locked_vm += vwork->npage;
-   up_write(>mmap_sem);
-   mmput(mm);
-   kfree(vwork);
-}
-
-static void vfio_lock_acct(struct task_struct *task, long npage)
+static int vfio_lock_acct(struct task_struct *task, long npage, bool *lock_cap)
 {
-   struct vwork *vwork;
struct mm_struct *mm;
bool is_current;
+   int ret;
 
if (!npage)
-   return;
+   return 0;
 
is_current = (task->mm == current->mm);
 

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Kirti Wankhede]

On 4/17/2017 8:02 PM, Alex Williamson wrote:
> On Mon, 17 Apr 2017 14:47:54 +0800
> Peter Xu  wrote:
> 
>> On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:
>>
>> [...]
>>
>>> -static void vfio_lock_acct(struct task_struct *task, long npage)
>>> +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
>>> lock_cap)
>>>  {
>>> -   struct vwork *vwork;
>>> struct mm_struct *mm;
>>> bool is_current;
>>> +   int ret;
>>>  
>>> if (!npage)
>>> -   return;
>>> +   return 0;
>>>  
>>> is_current = (task->mm == current->mm);
>>>  
>>> mm = is_current ? task->mm : get_task_mm(task);
>>> if (!mm)
>>> -   return; /* process exited */
>>> +   return -ESRCH; /* process exited */
>>>  
>>> -   if (down_write_trylock(>mmap_sem)) {
>>> -   mm->locked_vm += npage;
>>> -   up_write(>mmap_sem);
>>> -   if (!is_current)
>>> -   mmput(mm);
>>> -   return;
>>> -   }
>>> +   ret = down_write_killable(>mmap_sem);
>>> +   if (!ret) {
>>> +   if (npage < 0 || lock_cap) {  
>>
>> Nit: maybe we can avoid passing in lock_cap in all the callers of
>> vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
>> IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
>> need to pass in "false" any time when doing unpins.
> 
> Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
> since it tests whether the user is exceeding their locked memory
> limit.  The other callers could certainly get away with
> vfio_lock_acct() testing the capability itself but that would add a
> redundant call for the most common user.  I'm not a big fan of passing
> a lock_cap bool either, but it seemed the best fix for now.  The
> cleanest alternative I can up with is this (untested):
> 

In my opinion, passing 'bool lock_cap' looks much clean and simple.

Reviewed-by: Kirti Wankhede 

Thanks,
Kirti.

> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 07e0e58f22e9..0dbcf950fef9 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -246,7 +246,7 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, 
> struct vfio_pfn *vpfn)
>   return ret;
>  }
>  
> -static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> lock_cap)
> +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> *lock_cap)
>  {
>   struct mm_struct *mm;
>   bool is_current;
> @@ -263,19 +263,24 @@ static int vfio_lock_acct(struct task_struct *task, 
> long npage, bool lock_cap)
>  
>   ret = down_write_killable(>mmap_sem);
>   if (!ret) {
> - if (npage < 0 || lock_cap) {
> + if (npage < 0 || (lock_cap && *lock_cap)) {
>   mm->locked_vm += npage;
>   } else {
> - unsigned long limit;
> + if (lock_cap || !has_capability(task, CAP_IPC_LOCK)) {
> + unsigned long limit;
>  
> - limit = task_rlimit(task, RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> + limit = task_rlimit(task, RLIMIT_MEMLOCK)
> + >> PAGE_SHIFT;
>  
> - if (mm->locked_vm + npage <= limit)
> - mm->locked_vm += npage;
> - else
> - ret = -ENOMEM;
> - }
> + if (mm->locked_vm + npage > limit) {
> + ret = -ENOMEM;
> + goto upwrite;
> + }
> + }
>  
> + mm->locked_vm += npage;
> + }
> +upwrite:
>   up_write(>mmap_sem);
>   }
>  
> @@ -440,7 +445,7 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, 
> unsigned long vaddr,
>   }
>  
>  out:
> - ret = vfio_lock_acct(current, lock_acct, lock_cap);
> + ret = vfio_lock_acct(current, lock_acct, _cap);
>  
>  unpin_out:
>   if (ret) {
> @@ -471,7 +476,7 @@ static long vfio_unpin_pages_remote(struct vfio_dma *dma, 
> dma_addr_t iova,
>   }
>  
>   if (do_accounting)
> - vfio_lock_acct(dma->task, locked - unlocked, false);
> + vfio_lock_acct(dma->task, locked - unlocked, NULL);
>  
>   return unlocked;
>  }
> @@ -488,8 +493,7 @@ static int vfio_pin_page_external(struct vfio_dma *dma, 
> unsigned long vaddr,
>  
>   ret = vaddr_get_pfn(mm, vaddr, dma->prot, pfn_base);
>   if (!ret && do_accounting && !is_invalid_reserved_pfn(*pfn_base)) {
> - ret = vfio_lock_acct(dma->task, 1,
> -  has_capability(dma->task, CAP_IPC_LOCK));
> + ret = vfio_lock_acct(dma->task, 1, NULL);
>   if (ret)
>   

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Kirti Wankhede]

On 4/17/2017 8:02 PM, Alex Williamson wrote:
> On Mon, 17 Apr 2017 14:47:54 +0800
> Peter Xu  wrote:
> 
>> On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:
>>
>> [...]
>>
>>> -static void vfio_lock_acct(struct task_struct *task, long npage)
>>> +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
>>> lock_cap)
>>>  {
>>> -   struct vwork *vwork;
>>> struct mm_struct *mm;
>>> bool is_current;
>>> +   int ret;
>>>  
>>> if (!npage)
>>> -   return;
>>> +   return 0;
>>>  
>>> is_current = (task->mm == current->mm);
>>>  
>>> mm = is_current ? task->mm : get_task_mm(task);
>>> if (!mm)
>>> -   return; /* process exited */
>>> +   return -ESRCH; /* process exited */
>>>  
>>> -   if (down_write_trylock(>mmap_sem)) {
>>> -   mm->locked_vm += npage;
>>> -   up_write(>mmap_sem);
>>> -   if (!is_current)
>>> -   mmput(mm);
>>> -   return;
>>> -   }
>>> +   ret = down_write_killable(>mmap_sem);
>>> +   if (!ret) {
>>> +   if (npage < 0 || lock_cap) {  
>>
>> Nit: maybe we can avoid passing in lock_cap in all the callers of
>> vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
>> IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
>> need to pass in "false" any time when doing unpins.
> 
> Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
> since it tests whether the user is exceeding their locked memory
> limit.  The other callers could certainly get away with
> vfio_lock_acct() testing the capability itself but that would add a
> redundant call for the most common user.  I'm not a big fan of passing
> a lock_cap bool either, but it seemed the best fix for now.  The
> cleanest alternative I can up with is this (untested):
> 

In my opinion, passing 'bool lock_cap' looks much clean and simple.

Reviewed-by: Kirti Wankhede 

Thanks,
Kirti.

> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 07e0e58f22e9..0dbcf950fef9 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -246,7 +246,7 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, 
> struct vfio_pfn *vpfn)
>   return ret;
>  }
>  
> -static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> lock_cap)
> +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> *lock_cap)
>  {
>   struct mm_struct *mm;
>   bool is_current;
> @@ -263,19 +263,24 @@ static int vfio_lock_acct(struct task_struct *task, 
> long npage, bool lock_cap)
>  
>   ret = down_write_killable(>mmap_sem);
>   if (!ret) {
> - if (npage < 0 || lock_cap) {
> + if (npage < 0 || (lock_cap && *lock_cap)) {
>   mm->locked_vm += npage;
>   } else {
> - unsigned long limit;
> + if (lock_cap || !has_capability(task, CAP_IPC_LOCK)) {
> + unsigned long limit;
>  
> - limit = task_rlimit(task, RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> + limit = task_rlimit(task, RLIMIT_MEMLOCK)
> + >> PAGE_SHIFT;
>  
> - if (mm->locked_vm + npage <= limit)
> - mm->locked_vm += npage;
> - else
> - ret = -ENOMEM;
> - }
> + if (mm->locked_vm + npage > limit) {
> + ret = -ENOMEM;
> + goto upwrite;
> + }
> + }
>  
> + mm->locked_vm += npage;
> + }
> +upwrite:
>   up_write(>mmap_sem);
>   }
>  
> @@ -440,7 +445,7 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, 
> unsigned long vaddr,
>   }
>  
>  out:
> - ret = vfio_lock_acct(current, lock_acct, lock_cap);
> + ret = vfio_lock_acct(current, lock_acct, _cap);
>  
>  unpin_out:
>   if (ret) {
> @@ -471,7 +476,7 @@ static long vfio_unpin_pages_remote(struct vfio_dma *dma, 
> dma_addr_t iova,
>   }
>  
>   if (do_accounting)
> - vfio_lock_acct(dma->task, locked - unlocked, false);
> + vfio_lock_acct(dma->task, locked - unlocked, NULL);
>  
>   return unlocked;
>  }
> @@ -488,8 +493,7 @@ static int vfio_pin_page_external(struct vfio_dma *dma, 
> unsigned long vaddr,
>  
>   ret = vaddr_get_pfn(mm, vaddr, dma->prot, pfn_base);
>   if (!ret && do_accounting && !is_invalid_reserved_pfn(*pfn_base)) {
> - ret = vfio_lock_acct(dma->task, 1,
> -  has_capability(dma->task, CAP_IPC_LOCK));
> + ret = vfio_lock_acct(dma->task, 1, NULL);
>   if (ret)
>   put_pfn(*pfn_base, dma->prot);
>   }
> @@ 

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Alex Williamson]

On Mon, 17 Apr 2017 14:47:54 +0800
Peter Xu  wrote:

> On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:
> 
> [...]
> 
> > -static void vfio_lock_acct(struct task_struct *task, long npage)
> > +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> > lock_cap)
> >  {
> > -   struct vwork *vwork;
> > struct mm_struct *mm;
> > bool is_current;
> > +   int ret;
> >  
> > if (!npage)
> > -   return;
> > +   return 0;
> >  
> > is_current = (task->mm == current->mm);
> >  
> > mm = is_current ? task->mm : get_task_mm(task);
> > if (!mm)
> > -   return; /* process exited */
> > +   return -ESRCH; /* process exited */
> >  
> > -   if (down_write_trylock(>mmap_sem)) {
> > -   mm->locked_vm += npage;
> > -   up_write(>mmap_sem);
> > -   if (!is_current)
> > -   mmput(mm);
> > -   return;
> > -   }
> > +   ret = down_write_killable(>mmap_sem);
> > +   if (!ret) {
> > +   if (npage < 0 || lock_cap) {  
> 
> Nit: maybe we can avoid passing in lock_cap in all the callers of
> vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
> IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
> need to pass in "false" any time when doing unpins.

Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
since it tests whether the user is exceeding their locked memory
limit.  The other callers could certainly get away with
vfio_lock_acct() testing the capability itself but that would add a
redundant call for the most common user.  I'm not a big fan of passing
a lock_cap bool either, but it seemed the best fix for now.  The
cleanest alternative I can up with is this (untested):

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 07e0e58f22e9..0dbcf950fef9 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -246,7 +246,7 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, 
struct vfio_pfn *vpfn)
return ret;
 }
 
-static int vfio_lock_acct(struct task_struct *task, long npage, bool lock_cap)
+static int vfio_lock_acct(struct task_struct *task, long npage, bool *lock_cap)
 {
struct mm_struct *mm;
bool is_current;
@@ -263,19 +263,24 @@ static int vfio_lock_acct(struct task_struct *task, long 
npage, bool lock_cap)
 
ret = down_write_killable(>mmap_sem);
if (!ret) {
-   if (npage < 0 || lock_cap) {
+   if (npage < 0 || (lock_cap && *lock_cap)) {
mm->locked_vm += npage;
} else {
-   unsigned long limit;
+   if (lock_cap || !has_capability(task, CAP_IPC_LOCK)) {
+   unsigned long limit;
 
-   limit = task_rlimit(task, RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+   limit = task_rlimit(task, RLIMIT_MEMLOCK)
+   >> PAGE_SHIFT;
 
-   if (mm->locked_vm + npage <= limit)
-   mm->locked_vm += npage;
-   else
-   ret = -ENOMEM;
-   }
+   if (mm->locked_vm + npage > limit) {
+   ret = -ENOMEM;
+   goto upwrite;
+   }
+   }
 
+   mm->locked_vm += npage;
+   }
+upwrite:
up_write(>mmap_sem);
}
 
@@ -440,7 +445,7 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, 
unsigned long vaddr,
}
 
 out:
-   ret = vfio_lock_acct(current, lock_acct, lock_cap);
+   ret = vfio_lock_acct(current, lock_acct, _cap);
 
 unpin_out:
if (ret) {
@@ -471,7 +476,7 @@ static long vfio_unpin_pages_remote(struct vfio_dma *dma, 
dma_addr_t iova,
}
 
if (do_accounting)
-   vfio_lock_acct(dma->task, locked - unlocked, false);
+   vfio_lock_acct(dma->task, locked - unlocked, NULL);
 
return unlocked;
 }
@@ -488,8 +493,7 @@ static int vfio_pin_page_external(struct vfio_dma *dma, 
unsigned long vaddr,
 
ret = vaddr_get_pfn(mm, vaddr, dma->prot, pfn_base);
if (!ret && do_accounting && !is_invalid_reserved_pfn(*pfn_base)) {
-   ret = vfio_lock_acct(dma->task, 1,
-has_capability(dma->task, CAP_IPC_LOCK));
+   ret = vfio_lock_acct(dma->task, 1, NULL);
if (ret)
put_pfn(*pfn_base, dma->prot);
}
@@ -510,7 +514,7 @@ static int vfio_unpin_page_external(struct vfio_dma *dma, 
dma_addr_t iova,
unlocked = vfio_iova_put_vfio_pfn(dma, vpfn);
 
if (do_accounting)
-   vfio_lock_acct(dma->task, -unlocked, false);
+   

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Alex Williamson]

On Mon, 17 Apr 2017 14:47:54 +0800
Peter Xu  wrote:

> On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:
> 
> [...]
> 
> > -static void vfio_lock_acct(struct task_struct *task, long npage)
> > +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> > lock_cap)
> >  {
> > -   struct vwork *vwork;
> > struct mm_struct *mm;
> > bool is_current;
> > +   int ret;
> >  
> > if (!npage)
> > -   return;
> > +   return 0;
> >  
> > is_current = (task->mm == current->mm);
> >  
> > mm = is_current ? task->mm : get_task_mm(task);
> > if (!mm)
> > -   return; /* process exited */
> > +   return -ESRCH; /* process exited */
> >  
> > -   if (down_write_trylock(>mmap_sem)) {
> > -   mm->locked_vm += npage;
> > -   up_write(>mmap_sem);
> > -   if (!is_current)
> > -   mmput(mm);
> > -   return;
> > -   }
> > +   ret = down_write_killable(>mmap_sem);
> > +   if (!ret) {
> > +   if (npage < 0 || lock_cap) {  
> 
> Nit: maybe we can avoid passing in lock_cap in all the callers of
> vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
> IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
> need to pass in "false" any time when doing unpins.

Unfortunately vfio_pin_pages_remote() needs to know about lock_cap
since it tests whether the user is exceeding their locked memory
limit.  The other callers could certainly get away with
vfio_lock_acct() testing the capability itself but that would add a
redundant call for the most common user.  I'm not a big fan of passing
a lock_cap bool either, but it seemed the best fix for now.  The
cleanest alternative I can up with is this (untested):

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 07e0e58f22e9..0dbcf950fef9 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -246,7 +246,7 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, 
struct vfio_pfn *vpfn)
return ret;
 }
 
-static int vfio_lock_acct(struct task_struct *task, long npage, bool lock_cap)
+static int vfio_lock_acct(struct task_struct *task, long npage, bool *lock_cap)
 {
struct mm_struct *mm;
bool is_current;
@@ -263,19 +263,24 @@ static int vfio_lock_acct(struct task_struct *task, long 
npage, bool lock_cap)
 
ret = down_write_killable(>mmap_sem);
if (!ret) {
-   if (npage < 0 || lock_cap) {
+   if (npage < 0 || (lock_cap && *lock_cap)) {
mm->locked_vm += npage;
} else {
-   unsigned long limit;
+   if (lock_cap || !has_capability(task, CAP_IPC_LOCK)) {
+   unsigned long limit;
 
-   limit = task_rlimit(task, RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+   limit = task_rlimit(task, RLIMIT_MEMLOCK)
+   >> PAGE_SHIFT;
 
-   if (mm->locked_vm + npage <= limit)
-   mm->locked_vm += npage;
-   else
-   ret = -ENOMEM;
-   }
+   if (mm->locked_vm + npage > limit) {
+   ret = -ENOMEM;
+   goto upwrite;
+   }
+   }
 
+   mm->locked_vm += npage;
+   }
+upwrite:
up_write(>mmap_sem);
}
 
@@ -440,7 +445,7 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, 
unsigned long vaddr,
}
 
 out:
-   ret = vfio_lock_acct(current, lock_acct, lock_cap);
+   ret = vfio_lock_acct(current, lock_acct, _cap);
 
 unpin_out:
if (ret) {
@@ -471,7 +476,7 @@ static long vfio_unpin_pages_remote(struct vfio_dma *dma, 
dma_addr_t iova,
}
 
if (do_accounting)
-   vfio_lock_acct(dma->task, locked - unlocked, false);
+   vfio_lock_acct(dma->task, locked - unlocked, NULL);
 
return unlocked;
 }
@@ -488,8 +493,7 @@ static int vfio_pin_page_external(struct vfio_dma *dma, 
unsigned long vaddr,
 
ret = vaddr_get_pfn(mm, vaddr, dma->prot, pfn_base);
if (!ret && do_accounting && !is_invalid_reserved_pfn(*pfn_base)) {
-   ret = vfio_lock_acct(dma->task, 1,
-has_capability(dma->task, CAP_IPC_LOCK));
+   ret = vfio_lock_acct(dma->task, 1, NULL);
if (ret)
put_pfn(*pfn_base, dma->prot);
}
@@ -510,7 +514,7 @@ static int vfio_unpin_page_external(struct vfio_dma *dma, 
dma_addr_t iova,
unlocked = vfio_iova_put_vfio_pfn(dma, vpfn);
 
if (do_accounting)
-   vfio_lock_acct(dma->task, -unlocked, false);
+   

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Peter Xu]

On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:

[...]

> -static void vfio_lock_acct(struct task_struct *task, long npage)
> +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> lock_cap)
>  {
> - struct vwork *vwork;
>   struct mm_struct *mm;
>   bool is_current;
> + int ret;
>  
>   if (!npage)
> - return;
> + return 0;
>  
>   is_current = (task->mm == current->mm);
>  
>   mm = is_current ? task->mm : get_task_mm(task);
>   if (!mm)
> - return; /* process exited */
> + return -ESRCH; /* process exited */
>  
> - if (down_write_trylock(>mmap_sem)) {
> - mm->locked_vm += npage;
> - up_write(>mmap_sem);
> - if (!is_current)
> - mmput(mm);
> - return;
> - }
> + ret = down_write_killable(>mmap_sem);
> + if (!ret) {
> + if (npage < 0 || lock_cap) {

Nit: maybe we can avoid passing in lock_cap in all the callers of
vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
need to pass in "false" any time when doing unpins.

[...]

> @@ -405,7 +379,7 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned 
> long vaddr,
>  static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
> long npage, unsigned long *pfn_base)
>  {
> - unsigned long limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> + unsigned long pfn = 0, limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
>   bool lock_cap = capable(CAP_IPC_LOCK);
>   long ret, pinned = 0, lock_acct = 0;
>   bool rsvd;
> @@ -442,8 +416,6 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, 
> unsigned long vaddr,
>   /* Lock all the consecutive pages from pfn_base */
>   for (vaddr += PAGE_SIZE, iova += PAGE_SIZE; pinned < npage;
>pinned++, vaddr += PAGE_SIZE, iova += PAGE_SIZE) {
> - unsigned long pfn = 0;
> -
>   ret = vaddr_get_pfn(current->mm, vaddr, dma->prot, );
>   if (ret)
>   break;
> @@ -460,14 +432,25 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, 
> unsigned long vaddr,
>   put_pfn(pfn, dma->prot);
>   pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n",
>   __func__, limit << PAGE_SHIFT);
> - break;
> + ret = -ENOMEM;
> + goto unpin_out;
>   }
>   lock_acct++;
>   }
>   }
>  
>  out:
> - vfio_lock_acct(current, lock_acct);
> + ret = vfio_lock_acct(current, lock_acct, lock_cap);

I just didn't notice this in previous review, but... do we need to
check against !rsvd as well here before doing the accounting?

Thanks!

> +
> +unpin_out:
> + if (ret) {
> + if (!rsvd) {
> + for (pfn = *pfn_base ; pinned ; pfn++, pinned--)
> + put_pfn(pfn, dma->prot);
> + }
> +
> + return ret;
> + }
>  
>   return pinned;
>  }

-- 
Peter Xu

Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Peter Xu]

On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:

[...]

> -static void vfio_lock_acct(struct task_struct *task, long npage)
> +static int vfio_lock_acct(struct task_struct *task, long npage, bool 
> lock_cap)
>  {
> - struct vwork *vwork;
>   struct mm_struct *mm;
>   bool is_current;
> + int ret;
>  
>   if (!npage)
> - return;
> + return 0;
>  
>   is_current = (task->mm == current->mm);
>  
>   mm = is_current ? task->mm : get_task_mm(task);
>   if (!mm)
> - return; /* process exited */
> + return -ESRCH; /* process exited */
>  
> - if (down_write_trylock(>mmap_sem)) {
> - mm->locked_vm += npage;
> - up_write(>mmap_sem);
> - if (!is_current)
> - mmput(mm);
> - return;
> - }
> + ret = down_write_killable(>mmap_sem);
> + if (!ret) {
> + if (npage < 0 || lock_cap) {

Nit: maybe we can avoid passing in lock_cap in all the callers of
vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
need to pass in "false" any time when doing unpins.

[...]

> @@ -405,7 +379,7 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned 
> long vaddr,
>  static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
> long npage, unsigned long *pfn_base)
>  {
> - unsigned long limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> + unsigned long pfn = 0, limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
>   bool lock_cap = capable(CAP_IPC_LOCK);
>   long ret, pinned = 0, lock_acct = 0;
>   bool rsvd;
> @@ -442,8 +416,6 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, 
> unsigned long vaddr,
>   /* Lock all the consecutive pages from pfn_base */
>   for (vaddr += PAGE_SIZE, iova += PAGE_SIZE; pinned < npage;
>pinned++, vaddr += PAGE_SIZE, iova += PAGE_SIZE) {
> - unsigned long pfn = 0;
> -
>   ret = vaddr_get_pfn(current->mm, vaddr, dma->prot, );
>   if (ret)
>   break;
> @@ -460,14 +432,25 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, 
> unsigned long vaddr,
>   put_pfn(pfn, dma->prot);
>   pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n",
>   __func__, limit << PAGE_SHIFT);
> - break;
> + ret = -ENOMEM;
> + goto unpin_out;
>   }
>   lock_acct++;
>   }
>   }
>  
>  out:
> - vfio_lock_acct(current, lock_acct);
> + ret = vfio_lock_acct(current, lock_acct, lock_cap);

I just didn't notice this in previous review, but... do we need to
check against !rsvd as well here before doing the accounting?

Thanks!

> +
> +unpin_out:
> + if (ret) {
> + if (!rsvd) {
> + for (pfn = *pfn_base ; pinned ; pfn++, pinned--)
> + put_pfn(pfn, dma->prot);
> + }
> +
> + return ret;
> + }
>  
>   return pinned;
>  }

-- 
Peter Xu

[PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Alex Williamson]

If the mmap_sem is contented then the vfio type1 IOMMU backend will
defer locked page accounting updates to a workqueue task.  This has a
few problems and depending on which side the user tries to play, they
might be over-penalized for unmaps that haven't yet been accounted or
race the workqueue to enter more mappings than they're allowed.  The
original intent of this workqueue mechanism seems to be focused on
reducing latency through the ioctl, but we cannot do so at the cost
of correctness.  Remove this workqueue mechanism and update the
callers to allow for failure.  We can also now recheck the limit under
write lock to make sure we don't exceed it.

vfio_pin_pages_remote() also now necessarily includes an unwind path
which we can jump to directly if the consecutive page pinning finds
that we're exceeding the user's memory limits.  This avoids the
current lazy approach which does accounting and mapping up to the
fault, only to return an error on the next iteration to unwind the
entire vfio_dma.

Cc: sta...@vger.kernel.org
Signed-off-by: Alex Williamson 
---
 drivers/vfio/vfio_iommu_type1.c |  107 +--
 1 file changed, 48 insertions(+), 59 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 32d2633092a3..fb18e4a5df62 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -246,69 +246,43 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, 
struct vfio_pfn *vpfn)
return ret;
 }
 
-struct vwork {
-   struct mm_struct*mm;
-   longnpage;
-   struct work_struct  work;
-};
-
-/* delayed decrement/increment for locked_vm */
-static void vfio_lock_acct_bg(struct work_struct *work)
-{
-   struct vwork *vwork = container_of(work, struct vwork, work);
-   struct mm_struct *mm;
-
-   mm = vwork->mm;
-   down_write(>mmap_sem);
-   mm->locked_vm += vwork->npage;
-   up_write(>mmap_sem);
-   mmput(mm);
-   kfree(vwork);
-}
-
-static void vfio_lock_acct(struct task_struct *task, long npage)
+static int vfio_lock_acct(struct task_struct *task, long npage, bool lock_cap)
 {
-   struct vwork *vwork;
struct mm_struct *mm;
bool is_current;
+   int ret;
 
if (!npage)
-   return;
+   return 0;
 
is_current = (task->mm == current->mm);
 
mm = is_current ? task->mm : get_task_mm(task);
if (!mm)
-   return; /* process exited */
+   return -ESRCH; /* process exited */
 
-   if (down_write_trylock(>mmap_sem)) {
-   mm->locked_vm += npage;
-   up_write(>mmap_sem);
-   if (!is_current)
-   mmput(mm);
-   return;
-   }
+   ret = down_write_killable(>mmap_sem);
+   if (!ret) {
+   if (npage < 0 || lock_cap) {
+   mm->locked_vm += npage;
+   } else {
+   unsigned long limit;
 
-   if (is_current) {
-   mm = get_task_mm(task);
-   if (!mm)
-   return;
+   limit = task_rlimit(task, RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+
+   if (mm->locked_vm + npage <= limit)
+   mm->locked_vm += npage;
+   else
+   ret = -ENOMEM;
+   }
+
+   up_write(>mmap_sem);
}
 
-   /*
-* Couldn't get mmap_sem lock, so must setup to update
-* mm->locked_vm later. If locked_vm were atomic, we
-* wouldn't need this silliness
-*/
-   vwork = kmalloc(sizeof(struct vwork), GFP_KERNEL);
-   if (WARN_ON(!vwork)) {
+   if (!is_current)
mmput(mm);
-   return;
-   }
-   INIT_WORK(>work, vfio_lock_acct_bg);
-   vwork->mm = mm;
-   vwork->npage = npage;
-   schedule_work(>work);
+
+   return ret;
 }
 
 /*
@@ -405,7 +379,7 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned 
long vaddr,
 static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
  long npage, unsigned long *pfn_base)
 {
-   unsigned long limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+   unsigned long pfn = 0, limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
bool lock_cap = capable(CAP_IPC_LOCK);
long ret, pinned = 0, lock_acct = 0;
bool rsvd;
@@ -442,8 +416,6 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, 
unsigned long vaddr,
/* Lock all the consecutive pages from pfn_base */
for (vaddr += PAGE_SIZE, iova += PAGE_SIZE; pinned < npage;
 pinned++, vaddr += PAGE_SIZE, iova += PAGE_SIZE) {
-   unsigned long pfn = 0;
-
ret = vaddr_get_pfn(current->mm, vaddr, dma->prot, );
if (ret)
   

[PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

[Alex Williamson]

If the mmap_sem is contented then the vfio type1 IOMMU backend will
defer locked page accounting updates to a workqueue task.  This has a
few problems and depending on which side the user tries to play, they
might be over-penalized for unmaps that haven't yet been accounted or
race the workqueue to enter more mappings than they're allowed.  The
original intent of this workqueue mechanism seems to be focused on
reducing latency through the ioctl, but we cannot do so at the cost
of correctness.  Remove this workqueue mechanism and update the
callers to allow for failure.  We can also now recheck the limit under
write lock to make sure we don't exceed it.

vfio_pin_pages_remote() also now necessarily includes an unwind path
which we can jump to directly if the consecutive page pinning finds
that we're exceeding the user's memory limits.  This avoids the
current lazy approach which does accounting and mapping up to the
fault, only to return an error on the next iteration to unwind the
entire vfio_dma.

Cc: sta...@vger.kernel.org
Signed-off-by: Alex Williamson 
---
 drivers/vfio/vfio_iommu_type1.c |  107 +--
 1 file changed, 48 insertions(+), 59 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 32d2633092a3..fb18e4a5df62 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -246,69 +246,43 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, 
struct vfio_pfn *vpfn)
return ret;
 }
 
-struct vwork {
-   struct mm_struct*mm;
-   longnpage;
-   struct work_struct  work;
-};
-
-/* delayed decrement/increment for locked_vm */
-static void vfio_lock_acct_bg(struct work_struct *work)
-{
-   struct vwork *vwork = container_of(work, struct vwork, work);
-   struct mm_struct *mm;
-
-   mm = vwork->mm;
-   down_write(>mmap_sem);
-   mm->locked_vm += vwork->npage;
-   up_write(>mmap_sem);
-   mmput(mm);
-   kfree(vwork);
-}
-
-static void vfio_lock_acct(struct task_struct *task, long npage)
+static int vfio_lock_acct(struct task_struct *task, long npage, bool lock_cap)
 {
-   struct vwork *vwork;
struct mm_struct *mm;
bool is_current;
+   int ret;
 
if (!npage)
-   return;
+   return 0;
 
is_current = (task->mm == current->mm);
 
mm = is_current ? task->mm : get_task_mm(task);
if (!mm)
-   return; /* process exited */
+   return -ESRCH; /* process exited */
 
-   if (down_write_trylock(>mmap_sem)) {
-   mm->locked_vm += npage;
-   up_write(>mmap_sem);
-   if (!is_current)
-   mmput(mm);
-   return;
-   }
+   ret = down_write_killable(>mmap_sem);
+   if (!ret) {
+   if (npage < 0 || lock_cap) {
+   mm->locked_vm += npage;
+   } else {
+   unsigned long limit;
 
-   if (is_current) {
-   mm = get_task_mm(task);
-   if (!mm)
-   return;
+   limit = task_rlimit(task, RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+
+   if (mm->locked_vm + npage <= limit)
+   mm->locked_vm += npage;
+   else
+   ret = -ENOMEM;
+   }
+
+   up_write(>mmap_sem);
}
 
-   /*
-* Couldn't get mmap_sem lock, so must setup to update
-* mm->locked_vm later. If locked_vm were atomic, we
-* wouldn't need this silliness
-*/
-   vwork = kmalloc(sizeof(struct vwork), GFP_KERNEL);
-   if (WARN_ON(!vwork)) {
+   if (!is_current)
mmput(mm);
-   return;
-   }
-   INIT_WORK(>work, vfio_lock_acct_bg);
-   vwork->mm = mm;
-   vwork->npage = npage;
-   schedule_work(>work);
+
+   return ret;
 }
 
 /*
@@ -405,7 +379,7 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned 
long vaddr,
 static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
  long npage, unsigned long *pfn_base)
 {
-   unsigned long limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+   unsigned long pfn = 0, limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
bool lock_cap = capable(CAP_IPC_LOCK);
long ret, pinned = 0, lock_acct = 0;
bool rsvd;
@@ -442,8 +416,6 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, 
unsigned long vaddr,
/* Lock all the consecutive pages from pfn_base */
for (vaddr += PAGE_SIZE, iova += PAGE_SIZE; pinned < npage;
 pinned++, vaddr += PAGE_SIZE, iova += PAGE_SIZE) {
-   unsigned long pfn = 0;
-
ret = vaddr_get_pfn(current->mm, vaddr, dma->prot, );
if (ret)
break;
@@