linux-kernel - [PATCH v3 1/3] KVM: x86/mmu: Remove redundant spte present check in mmu_set

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Message-Id: <20210730225939.3852712-2-mizhang@google.com>
Date:   Fri, 30 Jul 2021 15:59:37 -0700
From:   Mingwei Zhang <mizhang@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.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>,
        Mingwei Zhang <mizhang@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        David Matlack <dmatlack@...gle.com>
Subject: [PATCH v3 1/3] KVM: x86/mmu: Remove redundant spte present check in mmu_set_spte

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@...gle.com>

Reviewed-by: Ben Gardon <bgardon@...gle.com>
Reviewed-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Mingwei Zhang <mizhang@...gle.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;
-- 
2.32.0.554.ge1b32706d8-goog