linux-kernel - Re: [PATCH v4 00/12] KVM: x86/mmu: refine memtype related mmu zap

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Date:   Wed,  4 Oct 2023 18:29:27 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Yan Zhao <yan.y.zhao@...el.com>
Cc:     pbonzini@...hat.com, chao.gao@...el.com, kai.huang@...el.com,
        robert.hoo.linux@...il.com, yuan.yao@...ux.intel.com
Subject: Re: [PATCH v4 00/12] KVM: x86/mmu: refine memtype related mmu zap

On Fri, 14 Jul 2023 14:46:56 +0800, Yan Zhao wrote:
> This series refines mmu zap caused by EPT memory type update when guest
> MTRRs are honored.
> 
> Patches 1-5 revolve around utilizing helper functions to check if
> KVM TDP honors guest MTRRs, TDP zaps and page fault max_level reduction
> are now only targeted to TDPs that honor guest MTRRs.
> 
> [...]

Applied 1-5 and 7 to kvm-x86 mmu.  I squashed 1 and 2 as introducing helpers to
consolidate existing code without converting the existing code is wierd and
makes it unnecessarily impossible to properly test the helpers when they're
added.

I skipped 6, "move TDP zaps from guest MTRRs update to CR0.CD toggling", for
now as your performance numbers showed that it slowed down the guest even
though the number of zaps went down.  I'm definitely not against the patch, I
just don't want to risk regressing guest performance, i.e. I don't wantt to
take it without the rest of the series that takes advantage of the change.

I massaged a few shortlogs and changelogs, but didn't touch any code.  Holler
if anything looks funky.

Thanks much!

[1/5] KVM: x86/mmu: Add helpers to return if KVM honors guest MTRRs
      https://github.com/kvm-x86/linux/commit/6590a37e7ec6
[2/5] KVM: x86/mmu: Zap SPTEs when CR0.CD is toggled iff guest MTRRs are honored
      https://github.com/kvm-x86/linux/commit/c0ad4a14c5af
[3/5] KVM: x86/mmu: Zap SPTEs on MTRR update iff guest MTRRs are honored
      https://github.com/kvm-x86/linux/commit/a1596812cce1
[4/5] KVM: x86/mmu: Xap KVM TDP when noncoherent DMA assignment starts/stops
      https://github.com/kvm-x86/linux/commit/3c4955c04b95
[5/5] KVM: VMX: drop IPAT in memtype when CD=1 for KVM_X86_QUIRK_CD_NW_CLEARED
      https://github.com/kvm-x86/linux/commit/f7b4bcd501ef

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