Re: [PATCH stable-4.9.y backport] KVM: arm/arm64: Don't reschedule in unmap_stage2_range()

[Marc Zyngier]

On 2020-08-24 12:29, Will Deacon wrote:
> Upstream commits fdfe7cbd5880 ("KVM: Pass MMU notifier range flags to
> kvm_unmap_hva_range()") and b5331379bc62 ("KVM: arm64: Only reschedule
> if MMU_NOTIFIER_RANGE_BLOCKABLE is not set") fix a "sleeping from 
> invalid
> context" BUG caused by unmap_stage2_range() attempting to reschedule 
> when
> called on the OOM path.
>
> Unfortunately, these patches rely on the MMU notifier callback being
> passed knowledge about whether or not blocking is permitted, which was
> introduced in 4.19. Rather than backport this considerable amount of
> infrastructure just for KVM on arm, instead just remove the conditional
> reschedule.
>
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.9 only
> Cc: Marc Zyngier <maz@xxxxxxxxxx>
> Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> Cc: James Morse <james.morse@xxxxxxx>
> Signed-off-by: Will Deacon <will@xxxxxxxxxx>
> ---
>  arch/arm/kvm/mmu.c | 6 ------
>  1 file changed, 6 deletions(-)
>
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index bb0d5e21d60b..b5ce1e81f945 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -298,12 +298,6 @@ static void unmap_stage2_range(struct kvm *kvm,
> phys_addr_t start, u64 size)
>  		next = stage2_pgd_addr_end(addr, end);
>  		if (!stage2_pgd_none(*pgd))
>  			unmap_stage2_puds(kvm, pgd, addr, next);
> -		/*
> -		 * If the range is too large, release the kvm->mmu_lock
> -		 * to prevent starvation and lockup detector warnings.
> -		 */
> -		if (next != end)
> -			cond_resched_lock(&kvm->mmu_lock);
>  	} while (pgd++, addr = next, addr != end);
>  }

Acked-by: Marc Zyngier <maz@xxxxxxxxxx>

        M.
--
Jazz is not dead. It just smells funny...