From: Sean Christopherson <seanjc@google.com>
To: Mingwei Zhang <mizhang@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Ben Gardon <bgardon@google.com>,
Jing Zhang <jingzhangos@google.com>
Subject: Re: [PATCH 1/2] kvm: mmu/x86: Remove redundant spte present check in mmu_set_spte
Date: Wed, 21 Jul 2021 16:27:13 +0000 [thread overview]
Message-ID: <YPhK4axwgv7+N5OG@google.com> (raw)
In-Reply-To: <20210721051247.355435-2-mizhang@google.com>
On Tue, Jul 20, 2021, Mingwei Zhang wrote:
> Drop an unnecessary is_shadow_present_pte() check when updating the rmaps
> after installing a non-MMIO SPTE. set_spte() is used only to create
> shadow-present SPTEs, e.g. MMIO SPTEs are handled early on, mmu_set_spte()
> runs with mmu_lock held for write, i.e. the SPTE can't be zapped between
> writing the SPTE and updating the rmaps.
>
> Opportunistically combine the "new SPTE" logic for large pages and rmaps.
Heh, except you forgot to actually do this in the code.
> No functional change intended.
>
> Suggested-by: Ben Gardon <bgardon@google.com>
> Signed-off-by: Mingwei Zhang <mizhang@google.com>
> ---
> arch/x86/kvm/mmu/mmu.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index b888385d1933..c45ddd2c964f 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2693,12 +2693,10 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
> if (!was_rmapped && is_large_pte(*sptep))
> ++vcpu->kvm->stat.lpages;
>
> - if (is_shadow_present_pte(*sptep)) {
> - if (!was_rmapped) {
> - rmap_count = rmap_add(vcpu, sptep, gfn);
> - if (rmap_count > RMAP_RECYCLE_THRESHOLD)
> - rmap_recycle(vcpu, sptep, gfn);
> - }
> + if (!was_rmapped) {
As above, this should be:
if (!was_rmapped) {
if (is_large_pte(*sptep))
++vcpu->kvm->stat.lpages;
> + rmap_count = rmap_add(vcpu, sptep, gfn);
> + if (rmap_count > RMAP_RECYCLE_THRESHOLD)
> + rmap_recycle(vcpu, sptep, gfn);
> }
>
> return ret;
> --
> 2.32.0.402.g57bb445576-goog
>
next prev parent reply other threads:[~2021-07-21 16:27 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-21 5:12 [PATCH 0/2] Add detailed page size stats in KVM stats Mingwei Zhang
2021-07-21 5:12 ` [PATCH 1/2] kvm: mmu/x86: Remove redundant spte present check in mmu_set_spte Mingwei Zhang
2021-07-21 16:27 ` Sean Christopherson [this message]
2021-07-21 5:12 ` [PATCH 2/2] kvm: mmu/x86: Add detailed page size stats Mingwei Zhang
2021-07-21 16:50 ` Ben Gardon
2021-07-21 18:34 ` Sean Christopherson
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