linux-kernel - [PATCH 1/2] kvm: mmu/x86: Remove redundant spte present check in mmu_set

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20210721051247.355435-2-mizhang@google.com>
Date:   Tue, 20 Jul 2021 22:12:46 -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>
Subject: [PATCH 1/2] kvm: mmu/x86: 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>
Signed-off-by: Mingwei Zhang <mizhang@...gle.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) {
+		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