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@lab.ntt.co.jp>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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;
@@ -896,7 +901,7 @@ 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;