[PATCH stable-4.14.y backport] KVM: arm/arm64: Don't reschedule in unmap_stage2_range()

[PATCH stable-4.14.y backport] KVM: arm/arm64: Don't reschedule in unmap_stage2_range()

[Will Deacon]

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@vger.kernel.org> # v4.14 only
Cc: Marc Zyngier <maz@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 virt/kvm/arm/mmu.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index 3814cdad643a..7fe673248e98 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -307,12 +307,6 @@ 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);
 }
 
-- 
2.28.0.297.g1956fa8f8d-goog

Re: [PATCH stable-4.14.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@vger.kernel.org> # v4.14 only
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  virt/kvm/arm/mmu.c | 6 ------
>  1 file changed, 6 deletions(-)
> 
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index 3814cdad643a..7fe673248e98 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -307,12 +307,6 @@ 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@kernel.org>

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