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
--
https://github.com/kvm-x86/linux/tree/next
