linux-kernel - Re: [PATCH v2 2/3] KVM: x86/mmu: Avoid collision with !PRESENT SPTEs in TDP MMU lpage stats

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Date:   Thu, 29 Jul 2021 12:01:00 -0700
From:   Mingwei Zhang <mizhang@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ben Gardon <bgardon@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>
Subject: Re: [PATCH v2 2/3] KVM: x86/mmu: Avoid collision with !PRESENT SPTEs
 in TDP MMU lpage stats

oh, definitely. Sorry for the confusion.

On Thu, Jul 29, 2021 at 11:34 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Mon, Jul 26, 2021, Mingwei Zhang wrote:
> > Factor in whether or not the old/new SPTEs are shadow-present when
> > adjusting the large page stats in the TDP MMU. A modified MMIO SPTE can
> > toggle the page size bit, as bit 7 is used to store the MMIO generation,
> > i.e. is_large_pte() can get a false positive when called on a MMIO SPTE.
> > Ditto for nuking SPTEs with REMOVED_SPTE, which sets bit 7 in its magic
> > value.
> >
> > Opportunistically move the logic below the check to verify at least one
> > of the old/new SPTEs is shadow present.
> >
> > Use is/was_leaf even though is/was_present would suffice.  The code
> > generation is roughly equivalent since all flags need to be computed
> > prior to the code in question, and using the *_leaf flags will minimize
> > the diff in a future enhancement to account all pages, i.e. will change
> > the check to "is_leaf != was_leaf".
> >
> > Suggested-by: Sean Christopherson <seanjc@...gle.com>
>
> There's no hard rule for when to use Suggested-by vs. giving Author credit, but
> in this case, since you took the patch and changelog verbatim[*] (sans the missing
> tags below), it's more polite to take the full patch (with me as Author in
> this case) and add your SOB since you're posting the patch.
>
>   Fixes: 1699f65c8b65 ("kvm/x86: Fix 'lpages' kvm stat for TDM MMU")
>   Cc: stable@...r.kernel.org
>
> [*] https://lkml.kernel.org/r/YPho0ME5pSjqRSoc@google.com
>
> > Signed-off-by: Mingwei Zhang <mizhang@...gle.com>