linux-kernel - [PATCH 02/12] KVM: MMU: properly check last spte in fast_page

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Date:	Tue, 30 Jul 2013 21:02:00 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	gleb@...hat.com
Cc:	avi.kivity@...il.com, mtosatti@...hat.com, pbonzini@...hat.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Subject: [PATCH 02/12] KVM: MMU: properly check last spte in fast_page_fault()

Using sp->role.level instead of @level since @level is not got from the
page table hierarchy

There is no issue in current code since the fast page fault only fixes the
fault caused by dirty-log, that means no large spte points to the dirty logged
page

The patch makes the code more readable and avoid potential issue in the further
development

Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
---
 arch/x86/kvm/mmu.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index a731c0b..cf163ca 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2830,9 +2830,9 @@ static bool page_fault_can_be_fast(u32 error_code)
 }
 
 static bool
-fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, u64 *sptep, u64 spte)
+fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
+			u64 *sptep, u64 spte)
 {
-	struct kvm_mmu_page *sp = page_header(__pa(sptep));
 	gfn_t gfn;
 
 	WARN_ON(!sp->role.direct);
@@ -2858,6 +2858,7 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
 			    u32 error_code)
 {
 	struct kvm_shadow_walk_iterator iterator;
+	struct kvm_mmu_page *sp;
 	bool ret = false;
 	u64 spte = 0ull;
 
@@ -2878,7 +2879,8 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
 		goto exit;
 	}
 
-	if (!is_last_spte(spte, level))
+	sp = page_header(__pa(iterator.sptep));
+	if (!is_last_spte(spte, sp->role.level))
 		goto exit;
 
 	/*
@@ -2904,7 +2906,7 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
 	 * the gfn is not stable for indirect shadow page.
 	 * See Documentation/virtual/kvm/locking.txt to get more detail.
 	 */
-	ret = fast_pf_fix_direct_spte(vcpu, iterator.sptep, spte);
+	ret = fast_pf_fix_direct_spte(vcpu, sp, iterator.sptep, spte);
 exit:
 	trace_fast_page_fault(vcpu, gva, error_code, iterator.sptep,
 			      spte, ret);
-- 
1.8.1.4

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