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

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Message-ID: <ff1d4de2-f3f8-eafa-6ba5-3e5bb715ae05@redhat.com>
Date:   Tue, 18 Aug 2020 08:31:08 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Will Deacon <will@...nel.org>, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Marc Zyngier <maz@...nel.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        James Morse <james.morse@....com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Mackerras <paulus@...abs.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH 0/2] KVM: arm64: Fix sleeping while atomic BUG() on OOM

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@...nel.org>
> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> Cc: James Morse <james.morse@....com>
> Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Cc: Paul Mackerras <paulus@...abs.org>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Sean Christopherson <sean.j.christopherson@...el.com>
> 
> --->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