linux-kernel - [RFC PATCH 3/8] KVM: x86/mmu: Refactor handling of not-present SPTEs in mmu_set

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Date:   Fri, 31 Jul 2020 14:23:18 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.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,
        eric van tassell <Eric.VanTassell@....com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: [RFC PATCH 3/8] KVM: x86/mmu: Refactor handling of not-present SPTEs in mmu_set_spte()

Return early from mmu_set_spte() if the new SPTE is not-present so as to
reduce the indentation of the code that performs metadata updates, e.g.
rmap manipulation.  Additional metadata updates will soon follow...

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/mmu/mmu.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 82f69a7456004..182f398036248 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3126,12 +3126,14 @@ 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);
-		}
+	/* No additional tracking necessary for not-present SPTEs. */
+	if (!is_shadow_present_pte(*sptep))
+		return ret;
+
+	if (!was_rmapped) {
+		rmap_count = rmap_add(vcpu, sptep, gfn);
+		if (rmap_count > RMAP_RECYCLE_THRESHOLD)
+			rmap_recycle(vcpu, sptep, gfn);
 	}
 
 	return ret;
-- 
2.28.0