linux-kernel - [PATCH 6/7] KVM: X86: Don't check unsync if the original spte is writible

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Date:   Tue, 24 Aug 2021 15:55:22 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        kvm@...r.kernel.org
Subject: [PATCH 6/7] KVM: X86: Don't check unsync if the original spte is writible

From: Lai Jiangshan <laijs@...ux.alibaba.com>

If the original spte is writable, the target gfn should not be the
gfn of synchronized shadowpage and can continue to be writable.

When !can_unsync, speculative must be false.  So when the check of
"!can_unsync" is removed, we need to move the label of "out" up.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 arch/x86/kvm/mmu/spte.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index b68a580f3510..a33c581aabd6 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -150,7 +150,7 @@ int make_spte(struct kvm_vcpu *vcpu, unsigned int pte_access, int level,
 		 * is responsibility of kvm_mmu_get_page / kvm_mmu_sync_roots.
 		 * Same reasoning can be applied to dirty page accounting.
 		 */
-		if (!can_unsync && is_writable_pte(old_spte))
+		if (is_writable_pte(old_spte))
 			goto out;
 
 		/*
@@ -171,10 +171,10 @@ int make_spte(struct kvm_vcpu *vcpu, unsigned int pte_access, int level,
 	if (pte_access & ACC_WRITE_MASK)
 		spte |= spte_shadow_dirty_mask(spte);
 
+out:
 	if (speculative)
 		spte = mark_spte_for_access_track(spte);
 
-out:
 	WARN_ONCE(is_rsvd_spte(&vcpu->arch.mmu->shadow_zero_check, spte, level),
 		  "spte = 0x%llx, level = %d, rsvd bits = 0x%llx", spte, level,
 		  get_rsvd_bits(&vcpu->arch.mmu->shadow_zero_check, spte, level));
-- 
2.19.1.6.gb485710b