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SubjectRe: [PATCH v2 1/3] KVM: x86/mmu: Remove redundant spte present check in mmu_set_spte
On Mon, Jul 26, 2021 at 10:54 AM Mingwei Zhang <mizhang@google.com> 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.
>
> No functional change intended.
>
> Suggested-by: Ben Gardon <bgardon@google.com>
> Signed-off-by: Mingwei Zhang <mizhang@google.com>

Reviewed-by: Ben Gardon <bgardon@google.com>

> ---
> arch/x86/kvm/mmu/mmu.c | 14 ++++++--------
> 1 file changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index b888385d1933..442cc554ebd6 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2690,15 +2690,13 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>
> pgprintk("%s: setting spte %llx\n", __func__, *sptep);
> trace_kvm_mmu_set_spte(level, gfn, 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) {
> + 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;
> --
> 2.32.0.432.gabb21c7263-goog
>

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