KVM: x86/mmu: Factor out allocating memslot rmap

Small refactor to facilitate allocating rmaps for all memslots at once.

No functional change expected.
Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20210518173414.450044-3-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -10941,10 +10941,31 @@ void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
 	kvm_page_track_free_memslot(slot);
 }
 
+static int memslot_rmap_alloc(struct kvm_memory_slot *slot,
+			      unsigned long npages)
+{
+	const int sz = sizeof(*slot->arch.rmap[0]);
+	int i;
+
+	for (i = 0; i < KVM_NR_PAGE_SIZES; ++i) {
+		int level = i + 1;
+		int lpages = gfn_to_index(slot->base_gfn + npages - 1,
+					  slot->base_gfn, level) + 1;
+
+		slot->arch.rmap[i] = kvcalloc(lpages, sz, GFP_KERNEL_ACCOUNT);
+		if (!slot->arch.rmap[i]) {
+			memslot_rmap_free(slot);
+			return -ENOMEM;
+		}
+	}
+
+	return 0;
+}
+
 static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
 				      unsigned long npages)
 {
-	int i;
+	int i, r;
 
 	/*
 	 * Clear out the previous array pointers for the KVM_MR_MOVE case.  The
@@ -10953,7 +10974,11 @@ static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
 	 */
 	memset(&slot->arch, 0, sizeof(slot->arch));
 
-	for (i = 0; i < KVM_NR_PAGE_SIZES; ++i) {
+	r = memslot_rmap_alloc(slot, npages);
+	if (r)
+		return r;
+
+	for (i = 1; i < KVM_NR_PAGE_SIZES; ++i) {
 		struct kvm_lpage_info *linfo;
 		unsigned long ugfn;
 		int lpages;
@@ -10962,14 +10987,6 @@ static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
 		lpages = gfn_to_index(slot->base_gfn + npages - 1,
 				      slot->base_gfn, level) + 1;
 
-		slot->arch.rmap[i] =
-			kvcalloc(lpages, sizeof(*slot->arch.rmap[i]),
-				 GFP_KERNEL_ACCOUNT);
-		if (!slot->arch.rmap[i])
-			goto out_free;
-		if (i == 0)
-			continue;
-
 		linfo = kvcalloc(lpages, sizeof(*linfo), GFP_KERNEL_ACCOUNT);
 		if (!linfo)
 			goto out_free;