KVM: MMU: Add link_shadow_page() helper

To simplify the process of fetching an spte, add a helper that links
a shadow page to an spte.
Reviewed-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/mmu.c

@@ -1482,6 +1482,16 @@ static void shadow_walk_next(struct kvm_shadow_walk_iterator *iterator)
 	--iterator->level;
 }
 
+static void link_shadow_page(u64 *sptep, struct kvm_mmu_page *sp)
+{
+	u64 spte;
+
+	spte = __pa(sp->spt)
+		| PT_PRESENT_MASK | PT_ACCESSED_MASK
+		| PT_WRITABLE_MASK | PT_USER_MASK;
+	*sptep = spte;
+}
+
 static void kvm_mmu_page_unlink_children(struct kvm *kvm,
 					 struct kvm_mmu_page *sp)
 {

arch/x86/kvm/paging_tmpl.h

@@ -309,7 +309,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 {
 	unsigned access = gw->pt_access;
 	struct kvm_mmu_page *sp;
-	u64 spte, *sptep = NULL;
+	u64 *sptep = NULL;
 	int direct;
 	gfn_t table_gfn;
 	int r;
@@ -395,10 +395,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 			}
 		}
 
-		spte = __pa(sp->spt)
-			| PT_PRESENT_MASK | PT_ACCESSED_MASK
-			| PT_WRITABLE_MASK | PT_USER_MASK;
-		*sptep = spte;
+		link_shadow_page(sptep, sp);
 	}
 
 	return sptep;