linux-kernel - [PATCH 09/11] KVM: MMU: remove the mismatch shadow page

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Date:	Tue, 26 Jul 2011 19:31:23 +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 09/11] KVM: MMU: remove the mismatch shadow page

If the shadow page has different cpu mode with current vcpu, we do better
remove them since the OS does not changes cpu mode frequently

Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
---
 arch/x86/kvm/mmu.c |   26 +++++++++++++++++++-------
 1 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 931c23a..2328ee6 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3603,6 +3603,18 @@ static bool detect_write_misaligned(struct kvm_mmu_page *sp, gpa_t gpa,
 	return misaligned;
 }
 
+/*
+ * The OS hardly changes cpu mode after boot, we can zap the shadow page if
+ * it is mismatched with the current vcpu.
+ */
+static bool detect_mismatch_sp(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
+{
+	union kvm_mmu_page_role mask;
+
+	mask.cr0_wp = mask.cr4_pae = mask.nxe = 1;
+	return (sp->role.word ^ vcpu->arch.mmu.base_role.word) & mask.word;
+}
+
 static u64 *get_written_sptes(struct kvm_mmu_page *sp, gpa_t gpa, int *nspte)
 {
 	unsigned page_offset, quadrant;
@@ -3638,13 +3650,12 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 		       const u8 *new, int bytes, bool repeat_write)
 {
 	gfn_t gfn = gpa >> PAGE_SHIFT;
-	union kvm_mmu_page_role mask = { .word = 0 };
 	struct kvm_mmu_page *sp;
 	struct hlist_node *node;
 	LIST_HEAD(invalid_list);
 	u64 entry, gentry, *spte;
 	int npte;
-	bool remote_flush, local_flush, zap_page, flooded, misaligned;
+	bool remote_flush, local_flush, zap_page, flooded;
 
 	/*
 	 * If we don't have indirect shadow pages, it means no page is
@@ -3664,10 +3675,13 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 	trace_kvm_mmu_audit(vcpu, AUDIT_PRE_PTE_WRITE);
 
 	flooded = detect_write_flooding(vcpu, gfn);
-	mask.cr0_wp = mask.cr4_pae = mask.nxe = 1;
 	for_each_gfn_indirect_valid_sp(vcpu->kvm, sp, gfn, node) {
+		bool mismatch, misaligned;
+
 		misaligned = detect_write_misaligned(sp, gpa, bytes);
-		if (misaligned || flooded || repeat_write) {
+		mismatch = detect_mismatch_sp(vcpu, sp);
+
+		if (misaligned || mismatch || flooded || repeat_write) {
 			zap_page |= !!kvm_mmu_prepare_zap_page(vcpu->kvm, sp,
 						     &invalid_list);
 			++vcpu->kvm->stat.mmu_flooded;
@@ -3682,9 +3696,7 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 		while (npte--) {
 			entry = *spte;
 			mmu_page_zap_pte(vcpu->kvm, sp, spte);
-			if (gentry &&
-			      !((sp->role.word ^ vcpu->arch.mmu.base_role.word)
-			      & mask.word) && get_free_pte_list_desc_nr(vcpu))
+			if (gentry && get_free_pte_list_desc_nr(vcpu))
 				mmu_pte_write_new_pte(vcpu, sp, spte, &gentry);
 			if (!remote_flush && need_remote_flush(entry, *spte))
 				remote_flush = true;
-- 
1.7.5.4

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