linux-kernel - [PATCH 1/4] KVM: MMU: don't drop spte if overwrite it from W to RO

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Date:	Fri, 12 Nov 2010 18:30:22 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: [PATCH 1/4] KVM: MMU: don't drop spte if overwrite it from W to RO

We just need flush tlb if overwrite a writable spte with a read-only one

Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
---
 arch/x86/kvm/mmu.c |   19 +++++++++----------
 1 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 4b6d54c..1a93ab4 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2044,6 +2044,15 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 	if (pte_access & ACC_WRITE_MASK)
 		mark_page_dirty(vcpu->kvm, gfn);
 
+	/*
+	 * If we overwrite a writable spte with a read-only one,
+	 * flush remote TLBs. Otherwise rmap_write_protect will
+	 * find a read-only spte, even though the writable spte
+	 * might be cached on a CPU's TLB.
+	 */
+	else if (is_writable_pte(*sptep))
+		ret = 1;
+
 set_pte:
 	update_spte(sptep, spte);
 done:
@@ -2084,16 +2093,6 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 				 spte_to_pfn(*sptep), pfn);
 			drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
 			kvm_flush_remote_tlbs(vcpu->kvm);
-		/*
-		 * If we overwrite a writable spte with a read-only one,
-		 * drop it and flush remote TLBs. Otherwise rmap_write_protect
-		 * will find a read-only spte, even though the writable spte
-		 * might be cached on a CPU's TLB.
-		 */
-		} else if (is_writable_pte(*sptep) &&
-			  (!(pte_access & ACC_WRITE_MASK) || !dirty)) {
-			drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
-			kvm_flush_remote_tlbs(vcpu->kvm);
 		} else
 			was_rmapped = 1;
 	}
-- 
1.7.0.4
--
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