Re: [PATCH 0/3] KVM: Performance and correctness fixes for CLEAR_DIRTY_LOG

[Sean Christopherson <seanjc@google.com>]

On Thu, Nov 30, 2023, Sean Christopherson wrote:
> On Fri, 27 Oct 2023 10:26:37 -0700, David Matlack wrote:
> > This series reduces the impact of CLEAR_DIRTY_LOG on guest performance
> > (Patch 3) and fixes 2 minor bugs found along the way (Patches 1 and 2).
> > 
> > We've observed that guest performance can drop while userspace is
> > issuing CLEAR_DIRTY_LOG ioctls and tracked down the problem to
> > contention on the mmu_lock in vCPU threads. CLEAR_DIRTY_LOG holds the
> > write-lock, so this isn't that surprising. We previously explored
> > converting CLEAR_DIRTY_LOG to hold the read-lock [1], but that has some
> > negative consequences:
> > 
> > [...]
> 
> Applied 1 and 2 to kvm-x86 mmu.  To get traction on #3, I recommend resending it
> as a standalone patch with all KVM arch maintainers Cc'd.
> 
> [1/3] KVM: x86/mmu: Fix off-by-1 when splitting huge pages during CLEAR
>       https://github.com/kvm-x86/linux/commit/7cd1bf039eeb
> [2/3] KVM: x86/mmu: Check for leaf SPTE when clearing dirty bit in the TDP MMU
>       https://github.com/kvm-x86/linux/commit/76d1492924bc

Force pushed because the Fixes: in patch 1 referenced a Google-internal commit.
New hashes:

[1/2] KVM: x86/mmu: Fix off-by-1 when splitting huge pages during CLEAR
      https://github.com/kvm-x86/linux/commit/1aa4bb916808
[2/2] KVM: x86/mmu: Check for leaf SPTE when clearing dirty bit in the TDP MMU
      https://github.com/kvm-x86/linux/commit/45a61ebb2211