linux-kernel - [PATCH 1/2] KVM: x86/mmu: Avoid multiple hash lookups in kvm_get_mmu

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Date:   Tue, 23 Jun 2020 12:40:26 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Peter Feiner <pfeiner@...gle.com>,
        Jon Cargille <jcargill@...gle.com>
Subject: [PATCH 1/2] KVM: x86/mmu: Avoid multiple hash lookups in kvm_get_mmu_page()

Refactor for_each_valid_sp() to take the list of shadow pages instead of
retrieving it from a gfn to avoid doing the gfn->list hash and lookup
multiple times during kvm_get_mmu_page().

Cc: Peter Feiner <pfeiner@...gle.com>
Cc: Jon Cargille <jcargill@...gle.com>
Cc: Jim Mattson <jmattson@...gle.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/mmu/mmu.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 3dd0af7e7515..67f8f82e9783 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2258,15 +2258,14 @@ static bool kvm_mmu_prepare_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp,
 static void kvm_mmu_commit_zap_page(struct kvm *kvm,
 				    struct list_head *invalid_list);
 
-
-#define for_each_valid_sp(_kvm, _sp, _gfn)				\
-	hlist_for_each_entry(_sp,					\
-	  &(_kvm)->arch.mmu_page_hash[kvm_page_table_hashfn(_gfn)], hash_link) \
+#define for_each_valid_sp(_kvm, _sp, _list)				\
+	hlist_for_each_entry(_sp, _list, hash_link)			\
 		if (is_obsolete_sp((_kvm), (_sp))) {			\
 		} else
 
 #define for_each_gfn_indirect_valid_sp(_kvm, _sp, _gfn)			\
-	for_each_valid_sp(_kvm, _sp, _gfn)				\
+	for_each_valid_sp(_kvm, _sp,					\
+	  &(_kvm)->arch.mmu_page_hash[kvm_page_table_hashfn(_gfn)])	\
 		if ((_sp)->gfn != (_gfn) || (_sp)->role.direct) {} else
 
 static inline bool is_ept_sp(struct kvm_mmu_page *sp)
@@ -2477,6 +2476,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 					     unsigned int access)
 {
 	union kvm_mmu_page_role role;
+	struct hlist_head *sp_list;
 	unsigned quadrant;
 	struct kvm_mmu_page *sp;
 	bool need_sync = false;
@@ -2496,7 +2496,9 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 		quadrant &= (1 << ((PT32_PT_BITS - PT64_PT_BITS) * level)) - 1;
 		role.quadrant = quadrant;
 	}
-	for_each_valid_sp(vcpu->kvm, sp, gfn) {
+
+	sp_list = &vcpu->kvm->arch.mmu_page_hash[kvm_page_table_hashfn(gfn)];
+	for_each_valid_sp(vcpu->kvm, sp, sp_list) {
 		if (sp->gfn != gfn) {
 			collisions++;
 			continue;
@@ -2533,8 +2535,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 
 	sp->gfn = gfn;
 	sp->role = role;
-	hlist_add_head(&sp->hash_link,
-		&vcpu->kvm->arch.mmu_page_hash[kvm_page_table_hashfn(gfn)]);
+	hlist_add_head(&sp->hash_link, sp_list);
 	if (!direct) {
 		/*
 		 * we should do write protection before syncing pages
-- 
2.26.0