linux-kernel - [PATCH 02/40] KVM: MMU: Simplify hash table indexing

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Date:	Mon, 31 Mar 2008 17:36:46 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	kvm-devel@...ts.sourceforge.net
Cc:	linux-kernel@...r.kernel.org, "Dong, Eddie" <eddie.dong@...el.com>
Subject: [PATCH 02/40] KVM: MMU: Simplify hash table indexing

From: Dong, Eddie <eddie.dong@...el.com>

Signed-off-by: Yaozu (Eddie) Dong <eddie.dong@...el.com>
Signed-off-by: Avi Kivity <avi@...ranet.com>
---
 arch/x86/kvm/mmu.c         |   10 +++++-----
 include/asm-x86/kvm_host.h |    3 ++-
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 28f9a44..6f8392d 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -559,7 +559,7 @@ static void kvm_mmu_free_page(struct kvm *kvm, struct kvm_mmu_page *sp)
 
 static unsigned kvm_page_table_hashfn(gfn_t gfn)
 {
-	return gfn;
+	return gfn & ((1 << KVM_MMU_HASH_SHIFT) - 1);
 }
 
 static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu,
@@ -663,7 +663,7 @@ static struct kvm_mmu_page *kvm_mmu_lookup_page(struct kvm *kvm, gfn_t gfn)
 	struct hlist_node *node;
 
 	pgprintk("%s: looking for gfn %lx\n", __FUNCTION__, gfn);
-	index = kvm_page_table_hashfn(gfn) % KVM_NUM_MMU_PAGES;
+	index = kvm_page_table_hashfn(gfn);
 	bucket = &kvm->arch.mmu_page_hash[index];
 	hlist_for_each_entry(sp, node, bucket, hash_link)
 		if (sp->gfn == gfn && !sp->role.metaphysical) {
@@ -701,7 +701,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 	}
 	pgprintk("%s: looking gfn %lx role %x\n", __FUNCTION__,
 		 gfn, role.word);
-	index = kvm_page_table_hashfn(gfn) % KVM_NUM_MMU_PAGES;
+	index = kvm_page_table_hashfn(gfn);
 	bucket = &vcpu->kvm->arch.mmu_page_hash[index];
 	hlist_for_each_entry(sp, node, bucket, hash_link)
 		if (sp->gfn == gfn && sp->role.word == role.word) {
@@ -840,7 +840,7 @@ static int kvm_mmu_unprotect_page(struct kvm *kvm, gfn_t gfn)
 
 	pgprintk("%s: looking for gfn %lx\n", __FUNCTION__, gfn);
 	r = 0;
-	index = kvm_page_table_hashfn(gfn) % KVM_NUM_MMU_PAGES;
+	index = kvm_page_table_hashfn(gfn);
 	bucket = &kvm->arch.mmu_page_hash[index];
 	hlist_for_each_entry_safe(sp, node, n, bucket, hash_link)
 		if (sp->gfn == gfn && !sp->role.metaphysical) {
@@ -1450,7 +1450,7 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 		vcpu->arch.last_pt_write_count = 1;
 		vcpu->arch.last_pte_updated = NULL;
 	}
-	index = kvm_page_table_hashfn(gfn) % KVM_NUM_MMU_PAGES;
+	index = kvm_page_table_hashfn(gfn);
 	bucket = &vcpu->kvm->arch.mmu_page_hash[index];
 	hlist_for_each_entry_safe(sp, node, n, bucket, hash_link) {
 		if (sp->gfn != gfn || sp->role.metaphysical)
diff --git a/include/asm-x86/kvm_host.h b/include/asm-x86/kvm_host.h
index 4702b04..d6db0de 100644
--- a/include/asm-x86/kvm_host.h
+++ b/include/asm-x86/kvm_host.h
@@ -57,7 +57,8 @@
 
 #define KVM_PERMILLE_MMU_PAGES 20
 #define KVM_MIN_ALLOC_MMU_PAGES 64
-#define KVM_NUM_MMU_PAGES 1024
+#define KVM_MMU_HASH_SHIFT 10
+#define KVM_NUM_MMU_PAGES (1 << KVM_MMU_HASH_SHIFT)
 #define KVM_MIN_FREE_MMU_PAGES 5
 #define KVM_REFILL_PAGES 25
 #define KVM_MAX_CPUID_ENTRIES 40
-- 
1.5.4.5

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