On 2020-08-24 12:28, 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 # v4.4 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

---

arch/arm/kvm/mmu.c | 8 -------- 1 file changed, 8 deletions(-)

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c index e0267532bd4e..edd392fdc14b 100644 --- a/arch/arm/kvm/mmu.c +++ b/arch/arm/kvm/mmu.c @@ -300,14 +300,6 @@ static void unmap_range(struct kvm *kvm, pgd_t *pgdp, next = kvm_pgd_addr_end(addr, end); if (!pgd_none(*pgd)) unmap_puds(kvm, pgd, addr, next);

• /*
  

•  * If we are dealing with a large range in
  

•  * stage2 table, release the kvm->mmu_lock
  

•  * to prevent starvation and lockup detector
  

•  * warnings.
  

•  */
  

• if (kvm && (next != end))
  

• 	cond_resched_lock(&kvm->mmu_lock);
  

  } while (pgd++, addr = next, addr != end);

}

Acked-by: Marc Zyngier maz@kernel.org

M.