linux-kernel - Re: [PATCH v2 3/3] KVM: x86/mmu: Add detailed page size stats

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Date:   Thu, 29 Jul 2021 18:45:30 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Ben Gardon <bgardon@...gle.com>
Cc:     Mingwei Zhang <mizhang@...gle.com>,
        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 <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jing Zhang <jingzhangos@...gle.com>
Subject: Re: [PATCH v2 3/3] KVM: x86/mmu: Add detailed page size stats

On Mon, Jul 26, 2021, Ben Gardon wrote:
> On Mon, Jul 26, 2021 at 10:54 AM Mingwei Zhang <mizhang@...gle.com> wrote:
> > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> > index 83e6c6965f1e..ad5638815311 100644
> > --- a/arch/x86/kvm/mmu.h
> > +++ b/arch/x86/kvm/mmu.h
> > @@ -240,4 +240,6 @@ static inline bool kvm_memslots_have_rmaps(struct kvm *kvm)
> >         return smp_load_acquire(&kvm->arch.memslots_have_rmaps);
> >  }
> >
> > +void kvm_update_page_stats(struct kvm *kvm, int level, int count);
> > +
> >  #endif
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 442cc554ebd6..7e0fc760739b 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -588,16 +588,22 @@ static bool mmu_spte_update(u64 *sptep, u64 new_spte)
> >         return flush;
> >  }
> >
> > +void kvm_update_page_stats(struct kvm *kvm, int level, int count)
> > +{
> > +       atomic64_add(count, &kvm->stat.page_stats.pages[level - 1]);
> > +}

This can be static inline in the header.  Ignoring prolog+RET, it's four instructions,
and two of those are sign extending input params.

> > +
> >  /*
> >   * Rules for using mmu_spte_clear_track_bits:
> >   * It sets the sptep from present to nonpresent, and track the
> >   * state bits, it is used to clear the last level sptep.
> >   * Returns non-zero if the PTE was previously valid.
> >   */
> > -static int mmu_spte_clear_track_bits(u64 *sptep)
> > +static int mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep)
> >  {
> >         kvm_pfn_t pfn;
> >         u64 old_spte = *sptep;
> > +       int level = sptep_to_sp(sptep)->role.level;
> >
> >         if (!spte_has_volatile_bits(old_spte))
> >                 __update_clear_spte_fast(sptep, 0ull);
> > @@ -607,6 +613,9 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
> >         if (!is_shadow_present_pte(old_spte))
> >                 return 0;
> >
> > +       if (is_last_spte(old_spte, level))
> 
> You can drop this check since it's part of the contract for calling
> this function.

Ah, nice!  I overlooked that.