Re: [PATCH] x86/kvm: Fix broken irq restoration in kvm_wait
On Sat, 13 Mar 2021 at 17:33, Paolo Bonzini wrote: > > On 13/03/21 01:57, Wanpeng Li wrote: > >> A third option would be to split the paths. In the end, it's only the > >> ptr/val > >> line that's shared. > > I just sent out a formal patch for my alternative fix, I think the > > whole logic in kvm_wait is more clear w/ my version. > > > > I don't know, having three "if"s in 10 lines of code is a bit daunting. Fair enough, just sent out v3 per Sean's suggestion. Wanpeng
Re: [PATCH] x86/kvm: Fix broken irq restoration in kvm_wait
On 13/03/21 01:57, Wanpeng Li wrote: A third option would be to split the paths. In the end, it's only the ptr/val line that's shared. I just sent out a formal patch for my alternative fix, I think the whole logic in kvm_wait is more clear w/ my version. I don't know, having three "if"s in 10 lines of code is a bit daunting. Paolo
Re: [PATCH] x86/kvm: Fix broken irq restoration in kvm_wait
On Thu, 11 Mar 2021 at 23:54, Sean Christopherson wrote:
>
> On Tue, Feb 23, 2021, Wanpeng Li wrote:
> > On Tue, 23 Feb 2021 at 13:25, Wanpeng Li wrote:
> > >
> > > From: Wanpeng Li
> > >
> > > After commit 997acaf6b4b59c (lockdep: report broken irq restoration), the
> > > guest
> > > splatting below during boot:
> > >
> > > raw_local_irq_restore() called with IRQs enabled
> > > WARNING: CPU: 1 PID: 169 at kernel/locking/irqflag-debug.c:10
> > > warn_bogus_irq_restore+0x26/0x30
> > > Modules linked in: hid_generic usbhid hid
> > > CPU: 1 PID: 169 Comm: systemd-udevd Not tainted 5.11.0+ #25
> > > RIP: 0010:warn_bogus_irq_restore+0x26/0x30
> > > Call Trace:
> > > kvm_wait+0x76/0x90
> > > __pv_queued_spin_lock_slowpath+0x285/0x2e0
> > > do_raw_spin_lock+0xc9/0xd0
> > > _raw_spin_lock+0x59/0x70
> > > lockref_get_not_dead+0xf/0x50
> > > __legitimize_path+0x31/0x60
> > > legitimize_root+0x37/0x50
> > > try_to_unlazy_next+0x7f/0x1d0
> > > lookup_fast+0xb0/0x170
> > > path_openat+0x165/0x9b0
> > > do_filp_open+0x99/0x110
> > > do_sys_openat2+0x1f1/0x2e0
> > > do_sys_open+0x5c/0x80
> > > __x64_sys_open+0x21/0x30
> > > do_syscall_64+0x32/0x50
> > > entry_SYSCALL_64_after_hwframe+0x44/0xae
> > >
> > > The irqflags handling in kvm_wait() which ends up doing:
> > >
> > > local_irq_save(flags);
> > > safe_halt();
> > > local_irq_restore(flags);
> > >
> > > which triggered a new consistency checking, we generally expect
> > > local_irq_save() and local_irq_restore() to be pared and sanely
> > > nested, and so local_irq_restore() expects to be called with
> > > irqs disabled.
> > >
> > > This patch fixes it by adding a local_irq_disable() after safe_halt()
> > > to avoid this warning.
> > >
> > > Cc: Mark Rutland
> > > Cc: Thomas Gleixner
> > > Signed-off-by: Wanpeng Li
> > > ---
> > > arch/x86/kernel/kvm.c | 4 +++-
> > > 1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> > > index 5e78e01..688c84a 100644
> > > --- a/arch/x86/kernel/kvm.c
> > > +++ b/arch/x86/kernel/kvm.c
> > > @@ -853,8 +853,10 @@ static void kvm_wait(u8 *ptr, u8 val)
> > > */
> > > if (arch_irqs_disabled_flags(flags))
> > > halt();
> > > - else
> > > + else {
> > > safe_halt();
> > > + local_irq_disable();
> > > + }
> >
> > An alternative fix:
> >
> > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> > index 5e78e01..7127aef 100644
> > --- a/arch/x86/kernel/kvm.c
> > +++ b/arch/x86/kernel/kvm.c
> > @@ -836,12 +836,13 @@ static void kvm_kick_cpu(int cpu)
> >
> > static void kvm_wait(u8 *ptr, u8 val)
> > {
> > -unsigned long flags;
> > +bool disabled = irqs_disabled();
> >
> > if (in_nmi())
> > return;
> >
> > -local_irq_save(flags);
> > +if (!disabled)
> > +local_irq_disable();
> >
> > if (READ_ONCE(*ptr) != val)
> > goto out;
> > @@ -851,13 +852,14 @@ static void kvm_wait(u8 *ptr, u8 val)
> > * for irq enabled case to avoid hang when lock info is overwritten
> > * in irq spinlock slowpath and no spurious interrupt occur to save us.
> > */
> > -if (arch_irqs_disabled_flags(flags))
> > +if (disabled)
> > halt();
> > else
> > safe_halt();
> >
> > out:
> > -local_irq_restore(flags);
> > +if (!disabled)
> > +local_irq_enable();
> > }
> >
> > #ifdef CONFIG_X86_32
>
> A third option would be to split the paths. In the end, it's only the ptr/val
> line that's shared.
I just sent out a formal patch for my alternative fix, I think the
whole logic in kvm_wait is more clear w/ my version.
>
> ---
> arch/x86/kernel/kvm.c | 23 ++-
> 1 file changed, 10 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 5e78e01ca3b4..78bb0fae3982 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -836,28 +836,25 @@ static void kvm_kick_cpu(int cpu)
>
> static void kvm_wait(u8 *ptr, u8 val)
> {
> - unsigned long flags;
> -
> if (in_nmi())
> return;
>
> - local_irq_save(flags);
> -
> - if (READ_ONCE(*ptr) != val)
> - goto out;
> -
> /*
> * halt until it's our turn and kicked. Note that we do safe halt
> * for irq enabled case to avoid hang when lock info is overwritten
> * in irq spinlock slowpath and no spurious interrupt occur to save
> us.
> */
> - if (arch_irqs_disabled_flags(flags))
> - halt();
> - else
> - safe_halt();
> + if (irqs_disabled()) {
> + if (READ_ONCE(*ptr) == val)
> + halt();
> + } else {
> + local_irq_disable();
>
> -out:
> - local_irq_restore(flags);
> + if (READ_ONCE(*ptr) == val)
> +
Re: [PATCH] x86/kvm: Fix broken irq restoration in kvm_wait
On 11/03/21 16:54, Sean Christopherson wrote:
On Tue, Feb 23, 2021, Wanpeng Li wrote:
On Tue, 23 Feb 2021 at 13:25, Wanpeng Li wrote:
From: Wanpeng Li
After commit 997acaf6b4b59c (lockdep: report broken irq restoration), the guest
splatting below during boot:
raw_local_irq_restore() called with IRQs enabled
WARNING: CPU: 1 PID: 169 at kernel/locking/irqflag-debug.c:10
warn_bogus_irq_restore+0x26/0x30
Modules linked in: hid_generic usbhid hid
CPU: 1 PID: 169 Comm: systemd-udevd Not tainted 5.11.0+ #25
RIP: 0010:warn_bogus_irq_restore+0x26/0x30
Call Trace:
kvm_wait+0x76/0x90
__pv_queued_spin_lock_slowpath+0x285/0x2e0
do_raw_spin_lock+0xc9/0xd0
_raw_spin_lock+0x59/0x70
lockref_get_not_dead+0xf/0x50
__legitimize_path+0x31/0x60
legitimize_root+0x37/0x50
try_to_unlazy_next+0x7f/0x1d0
lookup_fast+0xb0/0x170
path_openat+0x165/0x9b0
do_filp_open+0x99/0x110
do_sys_openat2+0x1f1/0x2e0
do_sys_open+0x5c/0x80
__x64_sys_open+0x21/0x30
do_syscall_64+0x32/0x50
entry_SYSCALL_64_after_hwframe+0x44/0xae
The irqflags handling in kvm_wait() which ends up doing:
local_irq_save(flags);
safe_halt();
local_irq_restore(flags);
which triggered a new consistency checking, we generally expect
local_irq_save() and local_irq_restore() to be pared and sanely
nested, and so local_irq_restore() expects to be called with
irqs disabled.
This patch fixes it by adding a local_irq_disable() after safe_halt()
to avoid this warning.
Cc: Mark Rutland
Cc: Thomas Gleixner
Signed-off-by: Wanpeng Li
---
arch/x86/kernel/kvm.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 5e78e01..688c84a 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -853,8 +853,10 @@ static void kvm_wait(u8 *ptr, u8 val)
*/
if (arch_irqs_disabled_flags(flags))
halt();
- else
+ else {
safe_halt();
+ local_irq_disable();
+ }
An alternative fix:
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 5e78e01..7127aef 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -836,12 +836,13 @@ static void kvm_kick_cpu(int cpu)
static void kvm_wait(u8 *ptr, u8 val)
{
-unsigned long flags;
+bool disabled = irqs_disabled();
if (in_nmi())
return;
-local_irq_save(flags);
+if (!disabled)
+local_irq_disable();
if (READ_ONCE(*ptr) != val)
goto out;
@@ -851,13 +852,14 @@ static void kvm_wait(u8 *ptr, u8 val)
* for irq enabled case to avoid hang when lock info is overwritten
* in irq spinlock slowpath and no spurious interrupt occur to save us.
*/
-if (arch_irqs_disabled_flags(flags))
+if (disabled)
halt();
else
safe_halt();
out:
-local_irq_restore(flags);
+if (!disabled)
+local_irq_enable();
}
#ifdef CONFIG_X86_32
A third option would be to split the paths. In the end, it's only the ptr/val
line that's shared.
---
arch/x86/kernel/kvm.c | 23 ++-
1 file changed, 10 insertions(+), 13 deletions(-)
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 5e78e01ca3b4..78bb0fae3982 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -836,28 +836,25 @@ static void kvm_kick_cpu(int cpu)
static void kvm_wait(u8 *ptr, u8 val)
{
- unsigned long flags;
-
if (in_nmi())
return;
- local_irq_save(flags);
-
- if (READ_ONCE(*ptr) != val)
- goto out;
-
/*
* halt until it's our turn and kicked. Note that we do safe halt
* for irq enabled case to avoid hang when lock info is overwritten
* in irq spinlock slowpath and no spurious interrupt occur to save us.
*/
- if (arch_irqs_disabled_flags(flags))
- halt();
- else
- safe_halt();
+ if (irqs_disabled()) {
+ if (READ_ONCE(*ptr) == val)
+ halt();
+ } else {
+ local_irq_disable();
-out:
- local_irq_restore(flags);
+ if (READ_ONCE(*ptr) == val)
+ safe_halt();
+
+ local_irq_enable();
+ }
}
#ifdef CONFIG_X86_32
--
I'll send this one tomorrow.
Paolo
Re: [PATCH] x86/kvm: Fix broken irq restoration in kvm_wait
On Tue, Feb 23, 2021, Wanpeng Li wrote:
> On Tue, 23 Feb 2021 at 13:25, Wanpeng Li wrote:
> >
> > From: Wanpeng Li
> >
> > After commit 997acaf6b4b59c (lockdep: report broken irq restoration), the
> > guest
> > splatting below during boot:
> >
> > raw_local_irq_restore() called with IRQs enabled
> > WARNING: CPU: 1 PID: 169 at kernel/locking/irqflag-debug.c:10
> > warn_bogus_irq_restore+0x26/0x30
> > Modules linked in: hid_generic usbhid hid
> > CPU: 1 PID: 169 Comm: systemd-udevd Not tainted 5.11.0+ #25
> > RIP: 0010:warn_bogus_irq_restore+0x26/0x30
> > Call Trace:
> > kvm_wait+0x76/0x90
> > __pv_queued_spin_lock_slowpath+0x285/0x2e0
> > do_raw_spin_lock+0xc9/0xd0
> > _raw_spin_lock+0x59/0x70
> > lockref_get_not_dead+0xf/0x50
> > __legitimize_path+0x31/0x60
> > legitimize_root+0x37/0x50
> > try_to_unlazy_next+0x7f/0x1d0
> > lookup_fast+0xb0/0x170
> > path_openat+0x165/0x9b0
> > do_filp_open+0x99/0x110
> > do_sys_openat2+0x1f1/0x2e0
> > do_sys_open+0x5c/0x80
> > __x64_sys_open+0x21/0x30
> > do_syscall_64+0x32/0x50
> > entry_SYSCALL_64_after_hwframe+0x44/0xae
> >
> > The irqflags handling in kvm_wait() which ends up doing:
> >
> > local_irq_save(flags);
> > safe_halt();
> > local_irq_restore(flags);
> >
> > which triggered a new consistency checking, we generally expect
> > local_irq_save() and local_irq_restore() to be pared and sanely
> > nested, and so local_irq_restore() expects to be called with
> > irqs disabled.
> >
> > This patch fixes it by adding a local_irq_disable() after safe_halt()
> > to avoid this warning.
> >
> > Cc: Mark Rutland
> > Cc: Thomas Gleixner
> > Signed-off-by: Wanpeng Li
> > ---
> > arch/x86/kernel/kvm.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> > index 5e78e01..688c84a 100644
> > --- a/arch/x86/kernel/kvm.c
> > +++ b/arch/x86/kernel/kvm.c
> > @@ -853,8 +853,10 @@ static void kvm_wait(u8 *ptr, u8 val)
> > */
> > if (arch_irqs_disabled_flags(flags))
> > halt();
> > - else
> > + else {
> > safe_halt();
> > + local_irq_disable();
> > + }
>
> An alternative fix:
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 5e78e01..7127aef 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -836,12 +836,13 @@ static void kvm_kick_cpu(int cpu)
>
> static void kvm_wait(u8 *ptr, u8 val)
> {
> -unsigned long flags;
> +bool disabled = irqs_disabled();
>
> if (in_nmi())
> return;
>
> -local_irq_save(flags);
> +if (!disabled)
> +local_irq_disable();
>
> if (READ_ONCE(*ptr) != val)
> goto out;
> @@ -851,13 +852,14 @@ static void kvm_wait(u8 *ptr, u8 val)
> * for irq enabled case to avoid hang when lock info is overwritten
> * in irq spinlock slowpath and no spurious interrupt occur to save us.
> */
> -if (arch_irqs_disabled_flags(flags))
> +if (disabled)
> halt();
> else
> safe_halt();
>
> out:
> -local_irq_restore(flags);
> +if (!disabled)
> +local_irq_enable();
> }
>
> #ifdef CONFIG_X86_32
A third option would be to split the paths. In the end, it's only the ptr/val
line that's shared.
---
arch/x86/kernel/kvm.c | 23 ++-
1 file changed, 10 insertions(+), 13 deletions(-)
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 5e78e01ca3b4..78bb0fae3982 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -836,28 +836,25 @@ static void kvm_kick_cpu(int cpu)
static void kvm_wait(u8 *ptr, u8 val)
{
- unsigned long flags;
-
if (in_nmi())
return;
- local_irq_save(flags);
-
- if (READ_ONCE(*ptr) != val)
- goto out;
-
/*
* halt until it's our turn and kicked. Note that we do safe halt
* for irq enabled case to avoid hang when lock info is overwritten
* in irq spinlock slowpath and no spurious interrupt occur to save us.
*/
- if (arch_irqs_disabled_flags(flags))
- halt();
- else
- safe_halt();
+ if (irqs_disabled()) {
+ if (READ_ONCE(*ptr) == val)
+ halt();
+ } else {
+ local_irq_disable();
-out:
- local_irq_restore(flags);
+ if (READ_ONCE(*ptr) == val)
+ safe_halt();
+
+ local_irq_enable();
+ }
}
#ifdef CONFIG_X86_32
--
Re: [PATCH] x86/kvm: Fix broken irq restoration in kvm_wait
ping,
On Tue, 23 Feb 2021 at 13:25, Wanpeng Li wrote:
>
> From: Wanpeng Li
>
> After commit 997acaf6b4b59c (lockdep: report broken irq restoration), the
> guest
> splatting below during boot:
>
> raw_local_irq_restore() called with IRQs enabled
> WARNING: CPU: 1 PID: 169 at kernel/locking/irqflag-debug.c:10
> warn_bogus_irq_restore+0x26/0x30
> Modules linked in: hid_generic usbhid hid
> CPU: 1 PID: 169 Comm: systemd-udevd Not tainted 5.11.0+ #25
> RIP: 0010:warn_bogus_irq_restore+0x26/0x30
> Call Trace:
> kvm_wait+0x76/0x90
> __pv_queued_spin_lock_slowpath+0x285/0x2e0
> do_raw_spin_lock+0xc9/0xd0
> _raw_spin_lock+0x59/0x70
> lockref_get_not_dead+0xf/0x50
> __legitimize_path+0x31/0x60
> legitimize_root+0x37/0x50
> try_to_unlazy_next+0x7f/0x1d0
> lookup_fast+0xb0/0x170
> path_openat+0x165/0x9b0
> do_filp_open+0x99/0x110
> do_sys_openat2+0x1f1/0x2e0
> do_sys_open+0x5c/0x80
> __x64_sys_open+0x21/0x30
> do_syscall_64+0x32/0x50
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> The irqflags handling in kvm_wait() which ends up doing:
>
> local_irq_save(flags);
> safe_halt();
> local_irq_restore(flags);
>
> which triggered a new consistency checking, we generally expect
> local_irq_save() and local_irq_restore() to be pared and sanely
> nested, and so local_irq_restore() expects to be called with
> irqs disabled.
>
> This patch fixes it by adding a local_irq_disable() after safe_halt()
> to avoid this warning.
>
> Cc: Mark Rutland
> Cc: Thomas Gleixner
> Signed-off-by: Wanpeng Li
> ---
> arch/x86/kernel/kvm.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 5e78e01..688c84a 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -853,8 +853,10 @@ static void kvm_wait(u8 *ptr, u8 val)
> */
> if (arch_irqs_disabled_flags(flags))
> halt();
> - else
> + else {
> safe_halt();
> + local_irq_disable();
> + }
>
> out:
> local_irq_restore(flags);
> --
> 2.7.4
>
Re: [PATCH] x86/kvm: Fix broken irq restoration in kvm_wait
On Tue, 23 Feb 2021 at 13:25, Wanpeng Li wrote:
>
> From: Wanpeng Li
>
> After commit 997acaf6b4b59c (lockdep: report broken irq restoration), the
> guest
> splatting below during boot:
>
> raw_local_irq_restore() called with IRQs enabled
> WARNING: CPU: 1 PID: 169 at kernel/locking/irqflag-debug.c:10
> warn_bogus_irq_restore+0x26/0x30
> Modules linked in: hid_generic usbhid hid
> CPU: 1 PID: 169 Comm: systemd-udevd Not tainted 5.11.0+ #25
> RIP: 0010:warn_bogus_irq_restore+0x26/0x30
> Call Trace:
> kvm_wait+0x76/0x90
> __pv_queued_spin_lock_slowpath+0x285/0x2e0
> do_raw_spin_lock+0xc9/0xd0
> _raw_spin_lock+0x59/0x70
> lockref_get_not_dead+0xf/0x50
> __legitimize_path+0x31/0x60
> legitimize_root+0x37/0x50
> try_to_unlazy_next+0x7f/0x1d0
> lookup_fast+0xb0/0x170
> path_openat+0x165/0x9b0
> do_filp_open+0x99/0x110
> do_sys_openat2+0x1f1/0x2e0
> do_sys_open+0x5c/0x80
> __x64_sys_open+0x21/0x30
> do_syscall_64+0x32/0x50
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> The irqflags handling in kvm_wait() which ends up doing:
>
> local_irq_save(flags);
> safe_halt();
> local_irq_restore(flags);
>
> which triggered a new consistency checking, we generally expect
> local_irq_save() and local_irq_restore() to be pared and sanely
> nested, and so local_irq_restore() expects to be called with
> irqs disabled.
>
> This patch fixes it by adding a local_irq_disable() after safe_halt()
> to avoid this warning.
>
> Cc: Mark Rutland
> Cc: Thomas Gleixner
> Signed-off-by: Wanpeng Li
> ---
> arch/x86/kernel/kvm.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 5e78e01..688c84a 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -853,8 +853,10 @@ static void kvm_wait(u8 *ptr, u8 val)
> */
> if (arch_irqs_disabled_flags(flags))
> halt();
> - else
> + else {
> safe_halt();
> + local_irq_disable();
> + }
An alternative fix:
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 5e78e01..7127aef 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -836,12 +836,13 @@ static void kvm_kick_cpu(int cpu)
static void kvm_wait(u8 *ptr, u8 val)
{
-unsigned long flags;
+bool disabled = irqs_disabled();
if (in_nmi())
return;
-local_irq_save(flags);
+if (!disabled)
+local_irq_disable();
if (READ_ONCE(*ptr) != val)
goto out;
@@ -851,13 +852,14 @@ static void kvm_wait(u8 *ptr, u8 val)
* for irq enabled case to avoid hang when lock info is overwritten
* in irq spinlock slowpath and no spurious interrupt occur to save us.
*/
-if (arch_irqs_disabled_flags(flags))
+if (disabled)
halt();
else
safe_halt();
out:
-local_irq_restore(flags);
+if (!disabled)
+local_irq_enable();
}
#ifdef CONFIG_X86_32
