Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[James Morse]

Hi gengdongjiu,

On 05/04/17 00:05, gengdongjiu wrote:
> thanks for the patch, have you consider to told Qemu or KVM tools
> the reason for this bus error(SEA/SEI)?

They should never need to know. We should treat Qemu/kvmtool like any other
program. Programs should only need to know about the affect on them, not the
underlying reason or mechanism.


> when Qemu or KVM tools get this SIGBUS signal, it do not know receive
> this SIGBUS due to SEA or SEI.

Why would this matter?

Firmware signalled Linux that something bad happened. Linux handles the problem
and everything keeps running.

The interface with firmware has to be architecture specific. When signalling
user-space it should be architecture agnostic, otherwise we can't write portable
user space code.


If Qemu was affected by the error (currently only if some of its memory was
hwpoisoned) we send it SIGBUS as we would for any other program. Qemu can choose
if and how to signal the guest about this error, it doesn't have to use the same
interface as firmware and the host used. With TCG Qemu may be emulating a
totally different architecture!


Looking at the list of errors in table 250 of UEFI 2.6, cache-errors are the
only case I can imagine we would want to report to a guest, these are
effectively transient memory errors. SIGBUS is still appropriate here, but we
probably need a new si_code value to indicate the error can be cleared. (unlike
hwpoison which appears to never re-use the affected page).


Thanks,

James
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Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[gengdongjiu]

Hi James,
   thanks for the patch, have you consider to told Qemu or KVM tools
the reason for this bus error(SEA/SEI)?

when Qemu or KVM tools get this SIGBUS signal, it do not know receive
this SIGBUS due to SEA or SEI.
OR KVM only send this SIGBUS when encounter SEA? if so, for the SEI
case, how to let Qemu simulate to generate CPER for guest OS SEI.


2017-03-16 0:07 GMT+08:00 James Morse :
> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], notifications for
> broken memory can call memory_failure() in mm/memory-failure.c to deliver
> SIGBUS to any user space process using the page, and notify all the
> in-kernel users.
>
> If the page corresponded with guest memory, KVM will unmap this page
> from its stage2 page tables. The user space process that allocated
> this memory may have never touched this page in which case it may not
> be mapped meaning SIGBUS won't be delivered.
>
> When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
> comes to process the stage2 fault.
>
> Do as x86 does, and deliver the SIGBUS when we discover
> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
> as this matches the user space mapping size.
>
> Signed-off-by: James Morse 
> CC: gengdongjiu 
> ---
>  Without this patch both kvmtool and Qemu exit as the KVM_RUN ioctl() returns
>  EFAULT.
>  QEMU: error: kvm run failed Bad address
>  LVKM: KVM_RUN failed: Bad address
>
>  With this patch both kvmtool and Qemu receive SIGBUS ... and then exit.
>  In the future Qemu can use this signal to notify the guest, for more details
>  see hwpoison[1].
>
>  [0] https://www.spinics.net/lists/arm-kernel/msg560009.html
>  [1] 
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/vm/hwpoison.txt
>
>
>  arch/arm/kvm/mmu.c | 23 +++
>  1 file changed, 23 insertions(+)
>
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 962616fd4ddd..9d1aa294e88f 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -20,8 +20,10 @@
>  #include 
>  #include 
>  #include 
> +#include 
>  #include 
>  #include 
> +#include 
>  #include 
>  #include 
>  #include 
> @@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct kvm_vcpu 
> *vcpu, kvm_pfn_t pfn,
> __coherent_cache_guest_page(vcpu, pfn, size);
>  }
>
> +static void kvm_send_hwpoison_signal(unsigned long address, bool hugetlb)
> +{
> +   siginfo_t info;
> +
> +   info.si_signo   = SIGBUS;
> +   info.si_errno   = 0;
> +   info.si_code= BUS_MCEERR_AR;
> +   info.si_addr= (void __user *)address;
> +
> +   if (hugetlb)
> +   info.si_addr_lsb = PMD_SHIFT;
> +   else
> +   info.si_addr_lsb = PAGE_SHIFT;
> +
> +   send_sig_info(SIGBUS, , current);
> +}
> +
>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>   struct kvm_memory_slot *memslot, unsigned long hva,
>   unsigned long fault_status)
> @@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, 
> phys_addr_t fault_ipa,
> smp_rmb();
>
> pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, );
> +   if (pfn == KVM_PFN_ERR_HWPOISON) {
> +   kvm_send_hwpoison_signal(hva, hugetlb);
> +   return 0;
> +   }
> if (is_error_noslot_pfn(pfn))
> return -EFAULT;
>
> --
> 2.10.1
>
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Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[Christoffer Dall]

On Tue, Mar 28, 2017 at 03:50:51PM +0100, Punit Agrawal wrote:
> Christoffer Dall  writes:
> 
> > On Mon, Mar 27, 2017 at 02:31:44PM +0100, Punit Agrawal wrote:
> >> Christoffer Dall  writes:
> >> 
> >> > On Mon, Mar 27, 2017 at 01:00:56PM +0100, James Morse wrote:
> >> >> Hi guys,
> >> >> 
> >> >> On 27/03/17 12:20, Punit Agrawal wrote:
> >> >> > Christoffer Dall  writes:
> >> >> >> On Wed, Mar 15, 2017 at 04:07:27PM +, James Morse wrote:
> >> >> >>> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], 
> >> >> >>> notifications for
> >> >> >>> broken memory can call memory_failure() in mm/memory-failure.c to 
> >> >> >>> deliver
> >> >> >>> SIGBUS to any user space process using the page, and notify all the
> >> >> >>> in-kernel users.
> >> >> >>>
> >> >> >>> If the page corresponded with guest memory, KVM will unmap this page
> >> >> >>> from its stage2 page tables. The user space process that allocated
> >> >> >>> this memory may have never touched this page in which case it may 
> >> >> >>> not
> >> >> >>> be mapped meaning SIGBUS won't be delivered.
> >> >> >>>
> >> >> >>> When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
> >> >> >>> comes to process the stage2 fault.
> >> >> >>>
> >> >> >>> Do as x86 does, and deliver the SIGBUS when we discover
> >> >> >>> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
> >> >> >>> as this matches the user space mapping size.
> >> >> 
> >> >> >>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> >> >> >>> index 962616fd4ddd..9d1aa294e88f 100644
> >> >> >>> --- a/arch/arm/kvm/mmu.c
> >> >> >>> +++ b/arch/arm/kvm/mmu.c
> >> >> >>> @@ -20,8 +20,10 @@
> >> >> >>>  #include 
> >> >> >>>  #include 
> >> >> >>>  #include 
> >> >> >>> +#include 
> >> >> >>>  #include 
> >> >> >>>  #include 
> >> >> >>> +#include 
> >> >> >>>  #include 
> >> >> >>>  #include 
> >> >> >>>  #include 
> >> >> >>> @@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct 
> >> >> >>> kvm_vcpu *vcpu, kvm_pfn_t pfn,
> >> >> >>> __coherent_cache_guest_page(vcpu, pfn, size);
> >> >> >>>  }
> >> >> >>>  
> >> >> >>> +static void kvm_send_hwpoison_signal(unsigned long address, bool 
> >> >> >>> hugetlb)
> >> >> >>> +{
> >> >> >>> +   siginfo_t info;
> >> >> >>> +
> >> >> >>> +   info.si_signo   = SIGBUS;
> >> >> >>> +   info.si_errno   = 0;
> >> >> >>> +   info.si_code= BUS_MCEERR_AR;
> >> >> >>> +   info.si_addr= (void __user *)address;
> >> >> >>> +
> >> >> >>> +   if (hugetlb)
> >> >> >>> +   info.si_addr_lsb = PMD_SHIFT;
> >> >> >>> +   else
> >> >> >>> +   info.si_addr_lsb = PAGE_SHIFT;
> >> >> >>> +
> >> >> >>> +   send_sig_info(SIGBUS, , current);
> >> >> >>> +}
> >> >> >>> +
> >> >> >>>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t 
> >> >> >>> fault_ipa,
> >> >> >>>   struct kvm_memory_slot *memslot, unsigned 
> >> >> >>> long hva,
> >> >> >>>   unsigned long fault_status)
> >> >> >>> @@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu 
> >> >> >>> *vcpu, phys_addr_t fault_ipa,
> >> >> >>> smp_rmb();
> >> >> >>>  
> >> >> >>> pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, );
> >> >> >>> +   if (pfn == KVM_PFN_ERR_HWPOISON) {
> >> >> >>> +   kvm_send_hwpoison_signal(hva, hugetlb);
> >> >> >>
> >> >> >> The way this is called means that we'll only notify userspace of a 
> >> >> >> huge
> >> >> >> mapping if userspace is mapping hugetlbfs, and not because the stage2
> >> >> >> mapping may or may not have used transparent huge pages when the 
> >> >> >> error
> >> >> >> was discovered.  Is this the desired semantics?
> >> >> 
> >> >> No,
> >> >> 
> >> >> 
> >> >> > I think so.
> >> >> >
> >> >> > AFAIUI, transparent hugepages are split before being poisoned while 
> >> >> > all
> >> >> > the underlying pages of a hugepage are poisoned together, i.e., no
> >> >> > splitting.
> >> >> 
> >> >> In which case I need to look into this some more!
> >> >> 
> >> >> My thinking was we should report the size that was knocked out of the 
> >> >> stage2 to
> >> >> avoid the guest repeatedly faulting until it has touched every 
> >> >> guest-page-size
> >> >> in the stage2 hole.
> >> >
> >> > By signaling something at the fault path, I think it's going to be very
> >> > hard to backtrack how the stage 2 page tables looked like when faults
> >> > started happening, because I think these are completely decoupled events
> >> > (the mmu notifier and the later fault).
> >> >
> >> >> 
> >> >> Reading the code in that kvm/mmu.c it looked like the mapping sizes 
> >> >> would always
> >> >> be the same as those used by userspace.
> >> >
> >> > I think the mapping sizes should be the same between userspace and KVM,
> >> > but the mapping size of a particular page (and associated pages) may
> >> > vary over time.
> >> 
> >> Stage 1 and Stage 2 support different hugepage sizes. A larger size
> >> 

Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[Punit Agrawal]

Christoffer Dall  writes:

> On Mon, Mar 27, 2017 at 02:31:44PM +0100, Punit Agrawal wrote:
>> Christoffer Dall  writes:
>> 
>> > On Mon, Mar 27, 2017 at 01:00:56PM +0100, James Morse wrote:
>> >> Hi guys,
>> >> 
>> >> On 27/03/17 12:20, Punit Agrawal wrote:
>> >> > Christoffer Dall  writes:
>> >> >> On Wed, Mar 15, 2017 at 04:07:27PM +, James Morse wrote:
>> >> >>> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], 
>> >> >>> notifications for
>> >> >>> broken memory can call memory_failure() in mm/memory-failure.c to 
>> >> >>> deliver
>> >> >>> SIGBUS to any user space process using the page, and notify all the
>> >> >>> in-kernel users.
>> >> >>>
>> >> >>> If the page corresponded with guest memory, KVM will unmap this page
>> >> >>> from its stage2 page tables. The user space process that allocated
>> >> >>> this memory may have never touched this page in which case it may not
>> >> >>> be mapped meaning SIGBUS won't be delivered.
>> >> >>>
>> >> >>> When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
>> >> >>> comes to process the stage2 fault.
>> >> >>>
>> >> >>> Do as x86 does, and deliver the SIGBUS when we discover
>> >> >>> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
>> >> >>> as this matches the user space mapping size.
>> >> 
>> >> >>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> >> >>> index 962616fd4ddd..9d1aa294e88f 100644
>> >> >>> --- a/arch/arm/kvm/mmu.c
>> >> >>> +++ b/arch/arm/kvm/mmu.c
>> >> >>> @@ -20,8 +20,10 @@
>> >> >>>  #include 
>> >> >>>  #include 
>> >> >>>  #include 
>> >> >>> +#include 
>> >> >>>  #include 
>> >> >>>  #include 
>> >> >>> +#include 
>> >> >>>  #include 
>> >> >>>  #include 
>> >> >>>  #include 
>> >> >>> @@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct 
>> >> >>> kvm_vcpu *vcpu, kvm_pfn_t pfn,
>> >> >>>   __coherent_cache_guest_page(vcpu, pfn, size);
>> >> >>>  }
>> >> >>>  
>> >> >>> +static void kvm_send_hwpoison_signal(unsigned long address, bool 
>> >> >>> hugetlb)
>> >> >>> +{
>> >> >>> + siginfo_t info;
>> >> >>> +
>> >> >>> + info.si_signo   = SIGBUS;
>> >> >>> + info.si_errno   = 0;
>> >> >>> + info.si_code= BUS_MCEERR_AR;
>> >> >>> + info.si_addr= (void __user *)address;
>> >> >>> +
>> >> >>> + if (hugetlb)
>> >> >>> + info.si_addr_lsb = PMD_SHIFT;
>> >> >>> + else
>> >> >>> + info.si_addr_lsb = PAGE_SHIFT;
>> >> >>> +
>> >> >>> + send_sig_info(SIGBUS, , current);
>> >> >>> +}
>> >> >>> +
>> >> >>>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t 
>> >> >>> fault_ipa,
>> >> >>> struct kvm_memory_slot *memslot, unsigned 
>> >> >>> long hva,
>> >> >>> unsigned long fault_status)
>> >> >>> @@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu 
>> >> >>> *vcpu, phys_addr_t fault_ipa,
>> >> >>>   smp_rmb();
>> >> >>>  
>> >> >>>   pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, );
>> >> >>> + if (pfn == KVM_PFN_ERR_HWPOISON) {
>> >> >>> + kvm_send_hwpoison_signal(hva, hugetlb);
>> >> >>
>> >> >> The way this is called means that we'll only notify userspace of a huge
>> >> >> mapping if userspace is mapping hugetlbfs, and not because the stage2
>> >> >> mapping may or may not have used transparent huge pages when the error
>> >> >> was discovered.  Is this the desired semantics?
>> >> 
>> >> No,
>> >> 
>> >> 
>> >> > I think so.
>> >> >
>> >> > AFAIUI, transparent hugepages are split before being poisoned while all
>> >> > the underlying pages of a hugepage are poisoned together, i.e., no
>> >> > splitting.
>> >> 
>> >> In which case I need to look into this some more!
>> >> 
>> >> My thinking was we should report the size that was knocked out of the 
>> >> stage2 to
>> >> avoid the guest repeatedly faulting until it has touched every 
>> >> guest-page-size
>> >> in the stage2 hole.
>> >
>> > By signaling something at the fault path, I think it's going to be very
>> > hard to backtrack how the stage 2 page tables looked like when faults
>> > started happening, because I think these are completely decoupled events
>> > (the mmu notifier and the later fault).
>> >
>> >> 
>> >> Reading the code in that kvm/mmu.c it looked like the mapping sizes would 
>> >> always
>> >> be the same as those used by userspace.
>> >
>> > I think the mapping sizes should be the same between userspace and KVM,
>> > but the mapping size of a particular page (and associated pages) may
>> > vary over time.
>> 
>> Stage 1 and Stage 2 support different hugepage sizes. A larger size
>> stage 1 page maps to multiple stage 2 page table entries. For stage 1,
>> we support PUD_SIZE, CONT_PMD_SIZE, PMD_SIZE and CONT_PTE_SIZE while
>> only PMD_SIZE is supported for Stage 2.
>> 
>> >
>> >> 
>> >> If the page was split before KVM could have taken this fault I assumed it 
>> >> would
>> >> fault on the 

Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[Christoffer Dall]

On Mon, Mar 27, 2017 at 02:31:44PM +0100, Punit Agrawal wrote:
> Christoffer Dall  writes:
> 
> > On Mon, Mar 27, 2017 at 01:00:56PM +0100, James Morse wrote:
> >> Hi guys,
> >> 
> >> On 27/03/17 12:20, Punit Agrawal wrote:
> >> > Christoffer Dall  writes:
> >> >> On Wed, Mar 15, 2017 at 04:07:27PM +, James Morse wrote:
> >> >>> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], notifications 
> >> >>> for
> >> >>> broken memory can call memory_failure() in mm/memory-failure.c to 
> >> >>> deliver
> >> >>> SIGBUS to any user space process using the page, and notify all the
> >> >>> in-kernel users.
> >> >>>
> >> >>> If the page corresponded with guest memory, KVM will unmap this page
> >> >>> from its stage2 page tables. The user space process that allocated
> >> >>> this memory may have never touched this page in which case it may not
> >> >>> be mapped meaning SIGBUS won't be delivered.
> >> >>>
> >> >>> When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
> >> >>> comes to process the stage2 fault.
> >> >>>
> >> >>> Do as x86 does, and deliver the SIGBUS when we discover
> >> >>> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
> >> >>> as this matches the user space mapping size.
> >> 
> >> >>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> >> >>> index 962616fd4ddd..9d1aa294e88f 100644
> >> >>> --- a/arch/arm/kvm/mmu.c
> >> >>> +++ b/arch/arm/kvm/mmu.c
> >> >>> @@ -20,8 +20,10 @@
> >> >>>  #include 
> >> >>>  #include 
> >> >>>  #include 
> >> >>> +#include 
> >> >>>  #include 
> >> >>>  #include 
> >> >>> +#include 
> >> >>>  #include 
> >> >>>  #include 
> >> >>>  #include 
> >> >>> @@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct 
> >> >>> kvm_vcpu *vcpu, kvm_pfn_t pfn,
> >> >>>__coherent_cache_guest_page(vcpu, pfn, size);
> >> >>>  }
> >> >>>  
> >> >>> +static void kvm_send_hwpoison_signal(unsigned long address, bool 
> >> >>> hugetlb)
> >> >>> +{
> >> >>> +  siginfo_t info;
> >> >>> +
> >> >>> +  info.si_signo   = SIGBUS;
> >> >>> +  info.si_errno   = 0;
> >> >>> +  info.si_code= BUS_MCEERR_AR;
> >> >>> +  info.si_addr= (void __user *)address;
> >> >>> +
> >> >>> +  if (hugetlb)
> >> >>> +  info.si_addr_lsb = PMD_SHIFT;
> >> >>> +  else
> >> >>> +  info.si_addr_lsb = PAGE_SHIFT;
> >> >>> +
> >> >>> +  send_sig_info(SIGBUS, , current);
> >> >>> +}
> >> >>> +
> >> >>>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t 
> >> >>> fault_ipa,
> >> >>>  struct kvm_memory_slot *memslot, unsigned 
> >> >>> long hva,
> >> >>>  unsigned long fault_status)
> >> >>> @@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu 
> >> >>> *vcpu, phys_addr_t fault_ipa,
> >> >>>smp_rmb();
> >> >>>  
> >> >>>pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, );
> >> >>> +  if (pfn == KVM_PFN_ERR_HWPOISON) {
> >> >>> +  kvm_send_hwpoison_signal(hva, hugetlb);
> >> >>
> >> >> The way this is called means that we'll only notify userspace of a huge
> >> >> mapping if userspace is mapping hugetlbfs, and not because the stage2
> >> >> mapping may or may not have used transparent huge pages when the error
> >> >> was discovered.  Is this the desired semantics?
> >> 
> >> No,
> >> 
> >> 
> >> > I think so.
> >> >
> >> > AFAIUI, transparent hugepages are split before being poisoned while all
> >> > the underlying pages of a hugepage are poisoned together, i.e., no
> >> > splitting.
> >> 
> >> In which case I need to look into this some more!
> >> 
> >> My thinking was we should report the size that was knocked out of the 
> >> stage2 to
> >> avoid the guest repeatedly faulting until it has touched every 
> >> guest-page-size
> >> in the stage2 hole.
> >
> > By signaling something at the fault path, I think it's going to be very
> > hard to backtrack how the stage 2 page tables looked like when faults
> > started happening, because I think these are completely decoupled events
> > (the mmu notifier and the later fault).
> >
> >> 
> >> Reading the code in that kvm/mmu.c it looked like the mapping sizes would 
> >> always
> >> be the same as those used by userspace.
> >
> > I think the mapping sizes should be the same between userspace and KVM,
> > but the mapping size of a particular page (and associated pages) may
> > vary over time.
> 
> Stage 1 and Stage 2 support different hugepage sizes. A larger size
> stage 1 page maps to multiple stage 2 page table entries. For stage 1,
> we support PUD_SIZE, CONT_PMD_SIZE, PMD_SIZE and CONT_PTE_SIZE while
> only PMD_SIZE is supported for Stage 2.
> 
> >
> >> 
> >> If the page was split before KVM could have taken this fault I assumed it 
> >> would
> >> fault on the page-size mapping and hugetlb would be false.
> >
> > I think you could have a huge page, which gets unmapped as a result on
> > it getting split (perhaps 

Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[Punit Agrawal]

Marc Zyngier  writes:

> On 27/03/17 14:31, Punit Agrawal wrote:
>> Christoffer Dall  writes:
>> 
>>> On Mon, Mar 27, 2017 at 01:00:56PM +0100, James Morse wrote:
 Hi guys,

 On 27/03/17 12:20, Punit Agrawal wrote:
> Christoffer Dall  writes:
>> On Wed, Mar 15, 2017 at 04:07:27PM +, James Morse wrote:
>>> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], notifications 
>>> for
>>> broken memory can call memory_failure() in mm/memory-failure.c to 
>>> deliver
>>> SIGBUS to any user space process using the page, and notify all the
>>> in-kernel users.
>>>
>>> If the page corresponded with guest memory, KVM will unmap this page
>>> from its stage2 page tables. The user space process that allocated
>>> this memory may have never touched this page in which case it may not
>>> be mapped meaning SIGBUS won't be delivered.
>>>
>>> When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
>>> comes to process the stage2 fault.
>>>
>>> Do as x86 does, and deliver the SIGBUS when we discover
>>> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
>>> as this matches the user space mapping size.

>>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>>> index 962616fd4ddd..9d1aa294e88f 100644
>>> --- a/arch/arm/kvm/mmu.c
>>> +++ b/arch/arm/kvm/mmu.c
>>> @@ -20,8 +20,10 @@
>>>  #include 
>>>  #include 
>>>  #include 
>>> +#include 
>>>  #include 
>>>  #include 
>>> +#include 
>>>  #include 
>>>  #include 
>>>  #include 
>>> @@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct 
>>> kvm_vcpu *vcpu, kvm_pfn_t pfn,
>>> __coherent_cache_guest_page(vcpu, pfn, size);
>>>  }
>>>  
>>> +static void kvm_send_hwpoison_signal(unsigned long address, bool 
>>> hugetlb)
>>> +{
>>> +   siginfo_t info;
>>> +
>>> +   info.si_signo   = SIGBUS;
>>> +   info.si_errno   = 0;
>>> +   info.si_code= BUS_MCEERR_AR;
>>> +   info.si_addr= (void __user *)address;
>>> +
>>> +   if (hugetlb)
>>> +   info.si_addr_lsb = PMD_SHIFT;
>>> +   else
>>> +   info.si_addr_lsb = PAGE_SHIFT;
>>> +
>>> +   send_sig_info(SIGBUS, , current);
>>> +}
>>> +
>>>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>>   struct kvm_memory_slot *memslot, unsigned 
>>> long hva,
>>>   unsigned long fault_status)
>>> @@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, 
>>> phys_addr_t fault_ipa,
>>> smp_rmb();
>>>  
>>> pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, );
>>> +   if (pfn == KVM_PFN_ERR_HWPOISON) {
>>> +   kvm_send_hwpoison_signal(hva, hugetlb);
>>
>> The way this is called means that we'll only notify userspace of a huge
>> mapping if userspace is mapping hugetlbfs, and not because the stage2
>> mapping may or may not have used transparent huge pages when the error
>> was discovered.  Is this the desired semantics?

 No,


> I think so.
>
> AFAIUI, transparent hugepages are split before being poisoned while all
> the underlying pages of a hugepage are poisoned together, i.e., no
> splitting.

 In which case I need to look into this some more!

 My thinking was we should report the size that was knocked out of the 
 stage2 to
 avoid the guest repeatedly faulting until it has touched every 
 guest-page-size
 in the stage2 hole.
>>>
>>> By signaling something at the fault path, I think it's going to be very
>>> hard to backtrack how the stage 2 page tables looked like when faults
>>> started happening, because I think these are completely decoupled events
>>> (the mmu notifier and the later fault).
>>>

 Reading the code in that kvm/mmu.c it looked like the mapping sizes would 
 always
 be the same as those used by userspace.
>>>
>>> I think the mapping sizes should be the same between userspace and KVM,
>>> but the mapping size of a particular page (and associated pages) may
>>> vary over time.
>> 
>> Stage 1 and Stage 2 support different hugepage sizes. A larger size
>> stage 1 page maps to multiple stage 2 page table entries. For stage 1,
>> we support PUD_SIZE, CONT_PMD_SIZE, PMD_SIZE and CONT_PTE_SIZE while
>> only PMD_SIZE is supported for Stage 2.
>
> What is stage-1 doing here? We have no idea about what stage-1 is doing
> (not under KVM's control). Or do you mean userspace instead?

I mean userspace here. Sorry for the confusion.

>
> Thanks,
>
>   M.
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Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[Marc Zyngier]

On 27/03/17 14:31, Punit Agrawal wrote:
> Christoffer Dall  writes:
> 
>> On Mon, Mar 27, 2017 at 01:00:56PM +0100, James Morse wrote:
>>> Hi guys,
>>>
>>> On 27/03/17 12:20, Punit Agrawal wrote:
 Christoffer Dall  writes:
> On Wed, Mar 15, 2017 at 04:07:27PM +, James Morse wrote:
>> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], notifications 
>> for
>> broken memory can call memory_failure() in mm/memory-failure.c to deliver
>> SIGBUS to any user space process using the page, and notify all the
>> in-kernel users.
>>
>> If the page corresponded with guest memory, KVM will unmap this page
>> from its stage2 page tables. The user space process that allocated
>> this memory may have never touched this page in which case it may not
>> be mapped meaning SIGBUS won't be delivered.
>>
>> When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
>> comes to process the stage2 fault.
>>
>> Do as x86 does, and deliver the SIGBUS when we discover
>> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
>> as this matches the user space mapping size.
>>>
>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> index 962616fd4ddd..9d1aa294e88f 100644
>> --- a/arch/arm/kvm/mmu.c
>> +++ b/arch/arm/kvm/mmu.c
>> @@ -20,8 +20,10 @@
>>  #include 
>>  #include 
>>  #include 
>> +#include 
>>  #include 
>>  #include 
>> +#include 
>>  #include 
>>  #include 
>>  #include 
>> @@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct 
>> kvm_vcpu *vcpu, kvm_pfn_t pfn,
>>  __coherent_cache_guest_page(vcpu, pfn, size);
>>  }
>>  
>> +static void kvm_send_hwpoison_signal(unsigned long address, bool 
>> hugetlb)
>> +{
>> +siginfo_t info;
>> +
>> +info.si_signo   = SIGBUS;
>> +info.si_errno   = 0;
>> +info.si_code= BUS_MCEERR_AR;
>> +info.si_addr= (void __user *)address;
>> +
>> +if (hugetlb)
>> +info.si_addr_lsb = PMD_SHIFT;
>> +else
>> +info.si_addr_lsb = PAGE_SHIFT;
>> +
>> +send_sig_info(SIGBUS, , current);
>> +}
>> +
>>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>struct kvm_memory_slot *memslot, unsigned 
>> long hva,
>>unsigned long fault_status)
>> @@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, 
>> phys_addr_t fault_ipa,
>>  smp_rmb();
>>  
>>  pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, );
>> +if (pfn == KVM_PFN_ERR_HWPOISON) {
>> +kvm_send_hwpoison_signal(hva, hugetlb);
>
> The way this is called means that we'll only notify userspace of a huge
> mapping if userspace is mapping hugetlbfs, and not because the stage2
> mapping may or may not have used transparent huge pages when the error
> was discovered.  Is this the desired semantics?
>>>
>>> No,
>>>
>>>
 I think so.

 AFAIUI, transparent hugepages are split before being poisoned while all
 the underlying pages of a hugepage are poisoned together, i.e., no
 splitting.
>>>
>>> In which case I need to look into this some more!
>>>
>>> My thinking was we should report the size that was knocked out of the 
>>> stage2 to
>>> avoid the guest repeatedly faulting until it has touched every 
>>> guest-page-size
>>> in the stage2 hole.
>>
>> By signaling something at the fault path, I think it's going to be very
>> hard to backtrack how the stage 2 page tables looked like when faults
>> started happening, because I think these are completely decoupled events
>> (the mmu notifier and the later fault).
>>
>>>
>>> Reading the code in that kvm/mmu.c it looked like the mapping sizes would 
>>> always
>>> be the same as those used by userspace.
>>
>> I think the mapping sizes should be the same between userspace and KVM,
>> but the mapping size of a particular page (and associated pages) may
>> vary over time.
> 
> Stage 1 and Stage 2 support different hugepage sizes. A larger size
> stage 1 page maps to multiple stage 2 page table entries. For stage 1,
> we support PUD_SIZE, CONT_PMD_SIZE, PMD_SIZE and CONT_PTE_SIZE while
> only PMD_SIZE is supported for Stage 2.

What is stage-1 doing here? We have no idea about what stage-1 is doing
(not under KVM's control). Or do you mean userspace instead?

Thanks,

M.
-- 
Jazz is not dead. It just smells funny...
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Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[Punit Agrawal]

Christoffer Dall  writes:

> On Mon, Mar 27, 2017 at 01:00:56PM +0100, James Morse wrote:
>> Hi guys,
>> 
>> On 27/03/17 12:20, Punit Agrawal wrote:
>> > Christoffer Dall  writes:
>> >> On Wed, Mar 15, 2017 at 04:07:27PM +, James Morse wrote:
>> >>> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], notifications 
>> >>> for
>> >>> broken memory can call memory_failure() in mm/memory-failure.c to deliver
>> >>> SIGBUS to any user space process using the page, and notify all the
>> >>> in-kernel users.
>> >>>
>> >>> If the page corresponded with guest memory, KVM will unmap this page
>> >>> from its stage2 page tables. The user space process that allocated
>> >>> this memory may have never touched this page in which case it may not
>> >>> be mapped meaning SIGBUS won't be delivered.
>> >>>
>> >>> When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
>> >>> comes to process the stage2 fault.
>> >>>
>> >>> Do as x86 does, and deliver the SIGBUS when we discover
>> >>> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
>> >>> as this matches the user space mapping size.
>> 
>> >>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> >>> index 962616fd4ddd..9d1aa294e88f 100644
>> >>> --- a/arch/arm/kvm/mmu.c
>> >>> +++ b/arch/arm/kvm/mmu.c
>> >>> @@ -20,8 +20,10 @@
>> >>>  #include 
>> >>>  #include 
>> >>>  #include 
>> >>> +#include 
>> >>>  #include 
>> >>>  #include 
>> >>> +#include 
>> >>>  #include 
>> >>>  #include 
>> >>>  #include 
>> >>> @@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct 
>> >>> kvm_vcpu *vcpu, kvm_pfn_t pfn,
>> >>>  __coherent_cache_guest_page(vcpu, pfn, size);
>> >>>  }
>> >>>  
>> >>> +static void kvm_send_hwpoison_signal(unsigned long address, bool 
>> >>> hugetlb)
>> >>> +{
>> >>> +siginfo_t info;
>> >>> +
>> >>> +info.si_signo   = SIGBUS;
>> >>> +info.si_errno   = 0;
>> >>> +info.si_code= BUS_MCEERR_AR;
>> >>> +info.si_addr= (void __user *)address;
>> >>> +
>> >>> +if (hugetlb)
>> >>> +info.si_addr_lsb = PMD_SHIFT;
>> >>> +else
>> >>> +info.si_addr_lsb = PAGE_SHIFT;
>> >>> +
>> >>> +send_sig_info(SIGBUS, , current);
>> >>> +}
>> >>> +
>> >>>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>> >>>struct kvm_memory_slot *memslot, unsigned 
>> >>> long hva,
>> >>>unsigned long fault_status)
>> >>> @@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, 
>> >>> phys_addr_t fault_ipa,
>> >>>  smp_rmb();
>> >>>  
>> >>>  pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, );
>> >>> +if (pfn == KVM_PFN_ERR_HWPOISON) {
>> >>> +kvm_send_hwpoison_signal(hva, hugetlb);
>> >>
>> >> The way this is called means that we'll only notify userspace of a huge
>> >> mapping if userspace is mapping hugetlbfs, and not because the stage2
>> >> mapping may or may not have used transparent huge pages when the error
>> >> was discovered.  Is this the desired semantics?
>> 
>> No,
>> 
>> 
>> > I think so.
>> >
>> > AFAIUI, transparent hugepages are split before being poisoned while all
>> > the underlying pages of a hugepage are poisoned together, i.e., no
>> > splitting.
>> 
>> In which case I need to look into this some more!
>> 
>> My thinking was we should report the size that was knocked out of the stage2 
>> to
>> avoid the guest repeatedly faulting until it has touched every 
>> guest-page-size
>> in the stage2 hole.
>
> By signaling something at the fault path, I think it's going to be very
> hard to backtrack how the stage 2 page tables looked like when faults
> started happening, because I think these are completely decoupled events
> (the mmu notifier and the later fault).
>
>> 
>> Reading the code in that kvm/mmu.c it looked like the mapping sizes would 
>> always
>> be the same as those used by userspace.
>
> I think the mapping sizes should be the same between userspace and KVM,
> but the mapping size of a particular page (and associated pages) may
> vary over time.

Stage 1 and Stage 2 support different hugepage sizes. A larger size
stage 1 page maps to multiple stage 2 page table entries. For stage 1,
we support PUD_SIZE, CONT_PMD_SIZE, PMD_SIZE and CONT_PTE_SIZE while
only PMD_SIZE is supported for Stage 2.

>
>> 
>> If the page was split before KVM could have taken this fault I assumed it 
>> would
>> fault on the page-size mapping and hugetlb would be false.
>
> I think you could have a huge page, which gets unmapped as a result on
> it getting split (perhaps because there was a failure on one page) and
> later as you fault, you can discover a range which can be a hugetlbfs or
> transparent huge pages.
>
> The question that I don't know is how Linux behaves if a page is marked
> with hwpoison, in that case, if Linux never supports THP and always
> 

Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[Christoffer Dall]

On Mon, Mar 27, 2017 at 01:00:56PM +0100, James Morse wrote:
> Hi guys,
> 
> On 27/03/17 12:20, Punit Agrawal wrote:
> > Christoffer Dall  writes:
> >> On Wed, Mar 15, 2017 at 04:07:27PM +, James Morse wrote:
> >>> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], notifications for
> >>> broken memory can call memory_failure() in mm/memory-failure.c to deliver
> >>> SIGBUS to any user space process using the page, and notify all the
> >>> in-kernel users.
> >>>
> >>> If the page corresponded with guest memory, KVM will unmap this page
> >>> from its stage2 page tables. The user space process that allocated
> >>> this memory may have never touched this page in which case it may not
> >>> be mapped meaning SIGBUS won't be delivered.
> >>>
> >>> When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
> >>> comes to process the stage2 fault.
> >>>
> >>> Do as x86 does, and deliver the SIGBUS when we discover
> >>> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
> >>> as this matches the user space mapping size.
> 
> >>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> >>> index 962616fd4ddd..9d1aa294e88f 100644
> >>> --- a/arch/arm/kvm/mmu.c
> >>> +++ b/arch/arm/kvm/mmu.c
> >>> @@ -20,8 +20,10 @@
> >>>  #include 
> >>>  #include 
> >>>  #include 
> >>> +#include 
> >>>  #include 
> >>>  #include 
> >>> +#include 
> >>>  #include 
> >>>  #include 
> >>>  #include 
> >>> @@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct 
> >>> kvm_vcpu *vcpu, kvm_pfn_t pfn,
> >>>   __coherent_cache_guest_page(vcpu, pfn, size);
> >>>  }
> >>>  
> >>> +static void kvm_send_hwpoison_signal(unsigned long address, bool hugetlb)
> >>> +{
> >>> + siginfo_t info;
> >>> +
> >>> + info.si_signo   = SIGBUS;
> >>> + info.si_errno   = 0;
> >>> + info.si_code= BUS_MCEERR_AR;
> >>> + info.si_addr= (void __user *)address;
> >>> +
> >>> + if (hugetlb)
> >>> + info.si_addr_lsb = PMD_SHIFT;
> >>> + else
> >>> + info.si_addr_lsb = PAGE_SHIFT;
> >>> +
> >>> + send_sig_info(SIGBUS, , current);
> >>> +}
> >>> +
> >>>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> >>> struct kvm_memory_slot *memslot, unsigned long hva,
> >>> unsigned long fault_status)
> >>> @@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, 
> >>> phys_addr_t fault_ipa,
> >>>   smp_rmb();
> >>>  
> >>>   pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, );
> >>> + if (pfn == KVM_PFN_ERR_HWPOISON) {
> >>> + kvm_send_hwpoison_signal(hva, hugetlb);
> >>
> >> The way this is called means that we'll only notify userspace of a huge
> >> mapping if userspace is mapping hugetlbfs, and not because the stage2
> >> mapping may or may not have used transparent huge pages when the error
> >> was discovered.  Is this the desired semantics?
> 
> No,
> 
> 
> > I think so.
> >
> > AFAIUI, transparent hugepages are split before being poisoned while all
> > the underlying pages of a hugepage are poisoned together, i.e., no
> > splitting.
> 
> In which case I need to look into this some more!
> 
> My thinking was we should report the size that was knocked out of the stage2 
> to
> avoid the guest repeatedly faulting until it has touched every guest-page-size
> in the stage2 hole.

By signaling something at the fault path, I think it's going to be very
hard to backtrack how the stage 2 page tables looked like when faults
started happening, because I think these are completely decoupled events
(the mmu notifier and the later fault).

> 
> Reading the code in that kvm/mmu.c it looked like the mapping sizes would 
> always
> be the same as those used by userspace.

I think the mapping sizes should be the same between userspace and KVM,
but the mapping size of a particular page (and associated pages) may
vary over time.

> 
> If the page was split before KVM could have taken this fault I assumed it 
> would
> fault on the page-size mapping and hugetlb would be false.

I think you could have a huge page, which gets unmapped as a result on
it getting split (perhaps because there was a failure on one page) and
later as you fault, you can discover a range which can be a hugetlbfs or
transparent huge pages.

The question that I don't know is how Linux behaves if a page is marked
with hwpoison, in that case, if Linux never supports THP and always
marks an entire huge page in a hugetlbfs with the poison, then I think
we're mostly good here.  If not, we should make sure we align with
whatever the rest of the kernel does.

> (which is already
> wrong for another reason, looks like I grabbed the variable before
> transparent_hugepage_adjust() has had a go a it.).
> 

yes, which is why I asked if you only care about hugetlbfs.

> 
> >> Also notice that the hva is not necessarily aligned to the beginning of
> >> the huge page, so can we be giving userspace wrong information by
> >> pointing in the middle of a huge page 

Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[James Morse]

Hi guys,

On 27/03/17 12:20, Punit Agrawal wrote:
> Christoffer Dall  writes:
>> On Wed, Mar 15, 2017 at 04:07:27PM +, James Morse wrote:
>>> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], notifications for
>>> broken memory can call memory_failure() in mm/memory-failure.c to deliver
>>> SIGBUS to any user space process using the page, and notify all the
>>> in-kernel users.
>>>
>>> If the page corresponded with guest memory, KVM will unmap this page
>>> from its stage2 page tables. The user space process that allocated
>>> this memory may have never touched this page in which case it may not
>>> be mapped meaning SIGBUS won't be delivered.
>>>
>>> When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
>>> comes to process the stage2 fault.
>>>
>>> Do as x86 does, and deliver the SIGBUS when we discover
>>> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
>>> as this matches the user space mapping size.

>>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>>> index 962616fd4ddd..9d1aa294e88f 100644
>>> --- a/arch/arm/kvm/mmu.c
>>> +++ b/arch/arm/kvm/mmu.c
>>> @@ -20,8 +20,10 @@
>>>  #include 
>>>  #include 
>>>  #include 
>>> +#include 
>>>  #include 
>>>  #include 
>>> +#include 
>>>  #include 
>>>  #include 
>>>  #include 
>>> @@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct 
>>> kvm_vcpu *vcpu, kvm_pfn_t pfn,
>>> __coherent_cache_guest_page(vcpu, pfn, size);
>>>  }
>>>  
>>> +static void kvm_send_hwpoison_signal(unsigned long address, bool hugetlb)
>>> +{
>>> +   siginfo_t info;
>>> +
>>> +   info.si_signo   = SIGBUS;
>>> +   info.si_errno   = 0;
>>> +   info.si_code= BUS_MCEERR_AR;
>>> +   info.si_addr= (void __user *)address;
>>> +
>>> +   if (hugetlb)
>>> +   info.si_addr_lsb = PMD_SHIFT;
>>> +   else
>>> +   info.si_addr_lsb = PAGE_SHIFT;
>>> +
>>> +   send_sig_info(SIGBUS, , current);
>>> +}
>>> +
>>>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>>   struct kvm_memory_slot *memslot, unsigned long hva,
>>>   unsigned long fault_status)
>>> @@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, 
>>> phys_addr_t fault_ipa,
>>> smp_rmb();
>>>  
>>> pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, );
>>> +   if (pfn == KVM_PFN_ERR_HWPOISON) {
>>> +   kvm_send_hwpoison_signal(hva, hugetlb);
>>
>> The way this is called means that we'll only notify userspace of a huge
>> mapping if userspace is mapping hugetlbfs, and not because the stage2
>> mapping may or may not have used transparent huge pages when the error
>> was discovered.  Is this the desired semantics?

No,


> I think so.
>
> AFAIUI, transparent hugepages are split before being poisoned while all
> the underlying pages of a hugepage are poisoned together, i.e., no
> splitting.

In which case I need to look into this some more!

My thinking was we should report the size that was knocked out of the stage2 to
avoid the guest repeatedly faulting until it has touched every guest-page-size
in the stage2 hole.

Reading the code in that kvm/mmu.c it looked like the mapping sizes would always
be the same as those used by userspace.

If the page was split before KVM could have taken this fault I assumed it would
fault on the page-size mapping and hugetlb would be false. (which is already
wrong for another reason, looks like I grabbed the variable before
transparent_hugepage_adjust() has had a go a it.).


>> Also notice that the hva is not necessarily aligned to the beginning of
>> the huge page, so can we be giving userspace wrong information by
>> pointing in the middle of a huge page and telling it there was an
>> address error in the size of the PMD ?
>>
> 
> I could be reading it wrong but I think we are fine here - the address
> (hva) is the location that faulted. And the lsb indicates the least
> significant bit of the faulting address (See man sigaction(2)). The
> receiver of the signal is expected to use the address and lsb to workout
> the extent of corruption.

kill_proc() in mm/memory-failure.c does this too, but the address is set by
page_address_in_vma() in add_to_kill() of the same file. (I'll chat with Punit
off list.)


> Though I missed a subtlety while reviewing the patch before. The
> reported lsb should be for the userspace hugepage mapping (i.e., hva)
> and not for the stage 2.

I thought these were always supposed to be the same, and using hugetlb was a bug
because I didn't look closely enough at what is_vm_hugetlb_page() does.


> In light of this, I'd like to retract my Reviewed-by tag for this
> version of the patch as I believe we'll need to change the lsb
> reporting.

Sure, lets work out what this should be doing. I'm beginning to suspect x86's
'always page size' was correct to begin with!


Thanks,

James
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Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[Punit Agrawal]

Christoffer Dall  writes:

> On Wed, Mar 15, 2017 at 04:07:27PM +, James Morse wrote:
>> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], notifications for
>> broken memory can call memory_failure() in mm/memory-failure.c to deliver
>> SIGBUS to any user space process using the page, and notify all the
>> in-kernel users.
>> 
>> If the page corresponded with guest memory, KVM will unmap this page
>> from its stage2 page tables. The user space process that allocated
>> this memory may have never touched this page in which case it may not
>> be mapped meaning SIGBUS won't be delivered.
>> 
>> When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
>> comes to process the stage2 fault.
>> 
>> Do as x86 does, and deliver the SIGBUS when we discover
>> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
>> as this matches the user space mapping size.
>> 
>> Signed-off-by: James Morse 
>> CC: gengdongjiu 
>> ---
>>  Without this patch both kvmtool and Qemu exit as the KVM_RUN ioctl() returns
>>  EFAULT.
>>  QEMU: error: kvm run failed Bad address
>>  LVKM: KVM_RUN failed: Bad address
>> 
>>  With this patch both kvmtool and Qemu receive SIGBUS ... and then exit.
>>  In the future Qemu can use this signal to notify the guest, for more details
>>  see hwpoison[1].
>> 
>>  [0] https://www.spinics.net/lists/arm-kernel/msg560009.html
>>  [1] 
>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/vm/hwpoison.txt
>> 
>> 
>>  arch/arm/kvm/mmu.c | 23 +++
>>  1 file changed, 23 insertions(+)
>> 
>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> index 962616fd4ddd..9d1aa294e88f 100644
>> --- a/arch/arm/kvm/mmu.c
>> +++ b/arch/arm/kvm/mmu.c
>> @@ -20,8 +20,10 @@
>>  #include 
>>  #include 
>>  #include 
>> +#include 
>>  #include 
>>  #include 
>> +#include 
>>  #include 
>>  #include 
>>  #include 
>> @@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct kvm_vcpu 
>> *vcpu, kvm_pfn_t pfn,
>>  __coherent_cache_guest_page(vcpu, pfn, size);
>>  }
>>  
>> +static void kvm_send_hwpoison_signal(unsigned long address, bool hugetlb)
>> +{
>> +siginfo_t info;
>> +
>> +info.si_signo   = SIGBUS;
>> +info.si_errno   = 0;
>> +info.si_code= BUS_MCEERR_AR;
>> +info.si_addr= (void __user *)address;
>> +
>> +if (hugetlb)
>> +info.si_addr_lsb = PMD_SHIFT;
>> +else
>> +info.si_addr_lsb = PAGE_SHIFT;
>> +
>> +send_sig_info(SIGBUS, , current);
>> +}
>> +
>>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>struct kvm_memory_slot *memslot, unsigned long hva,
>>unsigned long fault_status)
>> @@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, 
>> phys_addr_t fault_ipa,
>>  smp_rmb();
>>  
>>  pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, );
>> +if (pfn == KVM_PFN_ERR_HWPOISON) {
>> +kvm_send_hwpoison_signal(hva, hugetlb);
>
> The way this is called means that we'll only notify userspace of a huge
> mapping if userspace is mapping hugetlbfs, and not because the stage2
> mapping may or may not have used transparent huge pages when the error
> was discovered.  Is this the desired semantics?

I think so.

AFAIUI, transparent hugepages are split before being poisoned while all
the underlying pages of a hugepage are poisoned together, i.e., no
splitting.

>
> Also notice that the hva is not necessarily aligned to the beginning of
> the huge page, so can we be giving userspace wrong information by
> pointing in the middle of a huge page and telling it there was an
> address error in the size of the PMD ?
>

I could be reading it wrong but I think we are fine here - the address
(hva) is the location that faulted. And the lsb indicates the least
significant bit of the faulting address (See man sigaction(2)). The
receiver of the signal is expected to use the address and lsb to workout
the extent of corruption.

Though I missed a subtlety while reviewing the patch before. The
reported lsb should be for the userspace hugepage mapping (i.e., hva)
and not for the stage 2.

So in the case of hugepages the value of lsb should be -

huge_page_shift(hstate_vma(vma))

as the kernel supports more than just PMD size hugepages.

Does that make sense?

In light of this, I'd like to retract my Reviewed-by tag for this
version of the patch as I believe we'll need to change the lsb
reporting.

Thanks,
Punit

>> +return 0;
>> +}
>>  if (is_error_noslot_pfn(pfn))
>>  return -EFAULT;
>>  
>> -- 
>> 2.10.1
>> 
>
> Thanks,
> -Christoffer
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Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[Christoffer Dall]

On Wed, Mar 15, 2017 at 04:07:27PM +, James Morse wrote:
> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], notifications for
> broken memory can call memory_failure() in mm/memory-failure.c to deliver
> SIGBUS to any user space process using the page, and notify all the
> in-kernel users.
> 
> If the page corresponded with guest memory, KVM will unmap this page
> from its stage2 page tables. The user space process that allocated
> this memory may have never touched this page in which case it may not
> be mapped meaning SIGBUS won't be delivered.
> 
> When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
> comes to process the stage2 fault.
> 
> Do as x86 does, and deliver the SIGBUS when we discover
> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
> as this matches the user space mapping size.
> 
> Signed-off-by: James Morse 
> CC: gengdongjiu 
> ---
>  Without this patch both kvmtool and Qemu exit as the KVM_RUN ioctl() returns
>  EFAULT.
>  QEMU: error: kvm run failed Bad address
>  LVKM: KVM_RUN failed: Bad address
> 
>  With this patch both kvmtool and Qemu receive SIGBUS ... and then exit.
>  In the future Qemu can use this signal to notify the guest, for more details
>  see hwpoison[1].
> 
>  [0] https://www.spinics.net/lists/arm-kernel/msg560009.html
>  [1] 
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/vm/hwpoison.txt
> 
> 
>  arch/arm/kvm/mmu.c | 23 +++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 962616fd4ddd..9d1aa294e88f 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -20,8 +20,10 @@
>  #include 
>  #include 
>  #include 
> +#include 
>  #include 
>  #include 
> +#include 
>  #include 
>  #include 
>  #include 
> @@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct kvm_vcpu 
> *vcpu, kvm_pfn_t pfn,
>   __coherent_cache_guest_page(vcpu, pfn, size);
>  }
>  
> +static void kvm_send_hwpoison_signal(unsigned long address, bool hugetlb)
> +{
> + siginfo_t info;
> +
> + info.si_signo   = SIGBUS;
> + info.si_errno   = 0;
> + info.si_code= BUS_MCEERR_AR;
> + info.si_addr= (void __user *)address;
> +
> + if (hugetlb)
> + info.si_addr_lsb = PMD_SHIFT;
> + else
> + info.si_addr_lsb = PAGE_SHIFT;
> +
> + send_sig_info(SIGBUS, , current);
> +}
> +
>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> struct kvm_memory_slot *memslot, unsigned long hva,
> unsigned long fault_status)
> @@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, 
> phys_addr_t fault_ipa,
>   smp_rmb();
>  
>   pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, );
> + if (pfn == KVM_PFN_ERR_HWPOISON) {
> + kvm_send_hwpoison_signal(hva, hugetlb);

The way this is called means that we'll only notify userspace of a huge
mapping if userspace is mapping hugetlbfs, and not because the stage2
mapping may or may not have used transparent huge pages when the error
was discovered.  Is this the desired semantics?

Also notice that the hva is not necessarily aligned to the beginning of
the huge page, so can we be giving userspace wrong information by
pointing in the middle of a huge page and telling it there was an
address error in the size of the PMD ?

> + return 0;
> + }
>   if (is_error_noslot_pfn(pfn))
>   return -EFAULT;
>  
> -- 
> 2.10.1
> 

Thanks,
-Christoffer
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Re: [PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[Punit Agrawal]

Hi James,

One comment at the end.

James Morse  writes:

> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], notifications for
> broken memory can call memory_failure() in mm/memory-failure.c to deliver
> SIGBUS to any user space process using the page, and notify all the
> in-kernel users.
>
> If the page corresponded with guest memory, KVM will unmap this page
> from its stage2 page tables. The user space process that allocated
> this memory may have never touched this page in which case it may not
> be mapped meaning SIGBUS won't be delivered.
>
> When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
> comes to process the stage2 fault.
>
> Do as x86 does, and deliver the SIGBUS when we discover
> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
> as this matches the user space mapping size.
>
> Signed-off-by: James Morse 
> CC: gengdongjiu 
> ---
>  Without this patch both kvmtool and Qemu exit as the KVM_RUN ioctl() returns
>  EFAULT.
>  QEMU: error: kvm run failed Bad address
>  LVKM: KVM_RUN failed: Bad address
>
>  With this patch both kvmtool and Qemu receive SIGBUS ... and then exit.
>  In the future Qemu can use this signal to notify the guest, for more details
>  see hwpoison[1].
>
>  [0] https://www.spinics.net/lists/arm-kernel/msg560009.html
>  [1] 
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/vm/hwpoison.txt
>
>
>  arch/arm/kvm/mmu.c | 23 +++
>  1 file changed, 23 insertions(+)
>
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 962616fd4ddd..9d1aa294e88f 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -20,8 +20,10 @@
>  #include 
>  #include 
>  #include 
> +#include 
>  #include 
>  #include 
> +#include 
>  #include 
>  #include 
>  #include 
> @@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct kvm_vcpu 
> *vcpu, kvm_pfn_t pfn,
>   __coherent_cache_guest_page(vcpu, pfn, size);
>  }
>  
> +static void kvm_send_hwpoison_signal(unsigned long address, bool hugetlb)
> +{
> + siginfo_t info;
> +
> + info.si_signo   = SIGBUS;
> + info.si_errno   = 0;
> + info.si_code= BUS_MCEERR_AR;
> + info.si_addr= (void __user *)address;
> +
> + if (hugetlb)
> + info.si_addr_lsb = PMD_SHIFT;
> + else
> + info.si_addr_lsb = PAGE_SHIFT;
> +
> + send_sig_info(SIGBUS, , current);
> +}
> +
>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> struct kvm_memory_slot *memslot, unsigned long hva,
> unsigned long fault_status)
> @@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, 
> phys_addr_t fault_ipa,
>   smp_rmb();
>  
>   pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, );
> + if (pfn == KVM_PFN_ERR_HWPOISON) {
> + kvm_send_hwpoison_signal(hva, hugetlb);
> + return 0;
> + }
>   if (is_error_noslot_pfn(pfn))
>   return -EFAULT;

The changes look good to me. Though in essence as mentioned in the
commit log we are not doing anything different to x86 here. Worth moving
kvm_send_hwpoison_signal to an architecture agostic location and using
it from there?

In any case, FWIW,

Reviewed-by: Punit Agrawal 

Thanks.
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[PATCH] KVM: arm/arm64: Signal SIGBUS when stage2 discovers hwpoison memory

[James Morse]

Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64[0], notifications for
broken memory can call memory_failure() in mm/memory-failure.c to deliver
SIGBUS to any user space process using the page, and notify all the
in-kernel users.

If the page corresponded with guest memory, KVM will unmap this page
from its stage2 page tables. The user space process that allocated
this memory may have never touched this page in which case it may not
be mapped meaning SIGBUS won't be delivered.

When this happens KVM discovers pfn == KVM_PFN_ERR_HWPOISON when it
comes to process the stage2 fault.

Do as x86 does, and deliver the SIGBUS when we discover
KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb
as this matches the user space mapping size.

Signed-off-by: James Morse 
CC: gengdongjiu 
---
 Without this patch both kvmtool and Qemu exit as the KVM_RUN ioctl() returns
 EFAULT.
 QEMU: error: kvm run failed Bad address
 LVKM: KVM_RUN failed: Bad address

 With this patch both kvmtool and Qemu receive SIGBUS ... and then exit.
 In the future Qemu can use this signal to notify the guest, for more details
 see hwpoison[1].

 [0] https://www.spinics.net/lists/arm-kernel/msg560009.html
 [1] 
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/vm/hwpoison.txt


 arch/arm/kvm/mmu.c | 23 +++
 1 file changed, 23 insertions(+)

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 962616fd4ddd..9d1aa294e88f 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -20,8 +20,10 @@
 #include 
 #include 
 #include 
+#include 
 #include 
 #include 
+#include 
 #include 
 #include 
 #include 
@@ -1237,6 +1239,23 @@ static void coherent_cache_guest_page(struct kvm_vcpu 
*vcpu, kvm_pfn_t pfn,
__coherent_cache_guest_page(vcpu, pfn, size);
 }
 
+static void kvm_send_hwpoison_signal(unsigned long address, bool hugetlb)
+{
+   siginfo_t info;
+
+   info.si_signo   = SIGBUS;
+   info.si_errno   = 0;
+   info.si_code= BUS_MCEERR_AR;
+   info.si_addr= (void __user *)address;
+
+   if (hugetlb)
+   info.si_addr_lsb = PMD_SHIFT;
+   else
+   info.si_addr_lsb = PAGE_SHIFT;
+
+   send_sig_info(SIGBUS, , current);
+}
+
 static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
  struct kvm_memory_slot *memslot, unsigned long hva,
  unsigned long fault_status)
@@ -1306,6 +1325,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, 
phys_addr_t fault_ipa,
smp_rmb();
 
pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, );
+   if (pfn == KVM_PFN_ERR_HWPOISON) {
+   kvm_send_hwpoison_signal(hva, hugetlb);
+   return 0;
+   }
if (is_error_noslot_pfn(pfn))
return -EFAULT;
 
-- 
2.10.1

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