linux-kernel - [PATCH 5/5] KVM: x86: MMU: Eliminate an extra memory slot search in mapping

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Message-Id: <20151015194421.8c04134e3617b26816052e61@lab.ntt.co.jp>
Date:	Thu, 15 Oct 2015 19:44:21 +0900
From:	Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
To:	pbonzini@...hat.com
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 5/5] KVM: x86: MMU: Eliminate an extra memory slot search in
 mapping_level()

Calling kvm_vcpu_gfn_to_memslot() twice in mapping_level() should be
avoided since getting a slot by binary search may not be negligible,
especially for virtual machines with many memory slots.

Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
---
 arch/x86/kvm/mmu.c |   17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 78a3d08..8d285dc 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -818,14 +818,11 @@ static void unaccount_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)
 	kvm->arch.indirect_shadow_pages--;
 }
 
-static int has_wrprotected_page(struct kvm_vcpu *vcpu,
-				gfn_t gfn,
-				int level)
+static int __has_wrprotected_page(gfn_t gfn, int level,
+				  struct kvm_memory_slot *slot)
 {
-	struct kvm_memory_slot *slot;
 	struct kvm_lpage_info *linfo;
 
-	slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
 	if (slot) {
 		linfo = lpage_info_slot(gfn, slot, level);
 		return linfo->write_count;
@@ -834,6 +831,14 @@ static int has_wrprotected_page(struct kvm_vcpu *vcpu,
 	return 1;
 }
 
+static int has_wrprotected_page(struct kvm_vcpu *vcpu, gfn_t gfn, int level)
+{
+	struct kvm_memory_slot *slot;
+
+	slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
+	return __has_wrprotected_page(gfn, level, slot);
+}
+
 static int host_mapping_level(struct kvm *kvm, gfn_t gfn)
 {
 	unsigned long page_size;
@@ -893,7 +898,7 @@ static int mapping_level(struct kvm_vcpu *vcpu, gfn_t large_gfn,
 	max_level = min(kvm_x86_ops->get_lpage_level(), host_level);
 
 	for (level = PT_DIRECTORY_LEVEL; level <= max_level; ++level)
-		if (has_wrprotected_page(vcpu, large_gfn, level))
+		if (__has_wrprotected_page(large_gfn, level, slot))
 			break;
 
 	return level - 1;
-- 
1.7.9.5

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