Re: [PATCH 0/2] KVM: arm64: Fix sleeping while atomic BUG() on OOM

[Paolo Bonzini]

On 11/08/20 12:27, Will Deacon wrote:
> Hi all,
> 
> While stress-testing my arm64 stage-2 page-table rewrite [1], I ran into
> a sleeping while atomic BUG() during OOM that I can reproduce with
> mainline.
> 
> The problem is that the arm64 page-table code periodically calls
> cond_resched_lock() when unmapping the stage-2 page-tables, but in the
> case of OOM, this occurs in atomic context.
> 
> These couple of patches (based on 5.8) propagate the flags from the MMU
> notifier range structure, which in turn indicate whether or not blocking
> is permitted.
> 
> Cheers,
> 
> Will
> 
> [1] https://android-kvm.googlesource.com/linux/+/refs/heads/topic/pgtable
> 
> Cc: Marc Zyngier <maz@xxxxxxxxxx>
> Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> Cc: James Morse <james.morse@xxxxxxx>
> Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> 
> --->8
> 
> Will Deacon (2):
>   KVM: Pass MMU notifier range flags to kvm_unmap_hva_range()
>   KVM: arm64: Only reschedule if MMU_NOTIFIER_RANGE_BLOCKABLE is not set
> 
>  arch/arm64/include/asm/kvm_host.h   |  2 +-
>  arch/arm64/kvm/mmu.c                | 19 ++++++++++++++-----
>  arch/mips/include/asm/kvm_host.h    |  2 +-
>  arch/mips/kvm/mmu.c                 |  3 ++-
>  arch/powerpc/include/asm/kvm_host.h |  3 ++-
>  arch/powerpc/kvm/book3s.c           |  3 ++-
>  arch/powerpc/kvm/e500_mmu_host.c    |  3 ++-
>  arch/x86/include/asm/kvm_host.h     |  3 ++-
>  arch/x86/kvm/mmu/mmu.c              |  3 ++-
>  virt/kvm/kvm_main.c                 |  3 ++-
>  10 files changed, 30 insertions(+), 14 deletions(-)
> 

These would be okay for 5.9 too, so I plan to queue them myself before
we fork for 5.10.

Paolo