Re: [Patch v3 0/7] Optimize clear dirty log

Vipin Sharma
2023-03-21T18:12:33Z

On Mon, Mar 20, 2023 at 5:41 PM Sean Christopherson <seanjc@google.com> wrote:
>
> On Fri, Mar 17, 2023, Sean Christopherson wrote:
> > Did a cursory glance, looks good. I'll do a more thorough pass next week and get
> > it queued up if all goes well. No need for a v4 at this point, I'll fixup David's
> > various nits when applying.
>
> Ooof, that ended up being painful. In hindsight, I should have asked for a v4,
> but damage done, and it's my fault for throwing you a big blob of code in the
> first place.
>
> I ended up splitting the "interesting" patches into three each:
>
> 1. Switch to the atomic-AND
> 2. Drop the access-tracking / dirty-logging (as appropriate)
> 3. Drop the call to __handle_changed_spte()
>
> because logically they are three different things (although obviously related).
>
> I have pushed the result to kvm-x86/mmu, but haven't merged to kvm-x86/next or
> sent thanks because it's not yet tested. I'll do testing tomorrow, but if you
> can take a look in the meantime to make sure I didn't do something completely
> boneheaded, it'd be much appreciated.

Thanks for refactoring the patches. I reviewed the commits, no obvious
red flags from my side. Few small nits I found:

commit e534a94eac07 ("KVM: x86/mmu: Use kvm_ad_enabled() to determine
if TDP MMU SPTEs need wrprot")
- kvm_ad_enabled() should be outside the loop.

commit 69032b5d71ef (" KVM: x86/mmu: Atomically clear SPTE dirty state
in the clear-dirty-log flow")
- MMU_WARN_ON(kvm_ad_enabled() &&
spte_ad_need_write_protect(iter.old_spte) should be after
if(iter.level > PG_LEVEL_4k...)

commit 93c375bb6aea ("KVM: x86/mmu: Bypass __handle_changed_spte()
when clearing TDP MMU dirty bits")
- Needs new performance numbers. Adding MMU_WARN_ON() might change
numbers. I will run a perf test on your mmu branch and see if
something changes a lot.