kvm: commonize allocation of the new memory slots

commit f2a81036 upstream.

The two kmemdup invocations can be unified.  I find that the new
placement of the comment makes it easier to see what happens.
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

virt/kvm/kvm_main.c

@@ -841,11 +841,12 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			goto out_free;
 	}
 
+	slots = kmemdup(kvm->memslots, sizeof(struct kvm_memslots),
+			GFP_KERNEL);
+	if (!slots)
+		goto out_free;
+
 	if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) {
-		slots = kmemdup(kvm->memslots, sizeof(struct kvm_memslots),
-				GFP_KERNEL);
-		if (!slots)
-			goto out_free;
 		slot = id_to_memslot(slots, mem->slot);
 		slot->flags |= KVM_MEMSLOT_INVALID;
 
@@ -861,6 +862,12 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		 * 	- kvm_is_visible_gfn (mmu_check_roots)
 		 */
 		kvm_arch_flush_shadow_memslot(kvm, slot);
+
+		/*
+		 * We can re-use the old_memslots from above, the only difference
+		 * from the currently installed memslots is the invalid flag.  This
+		 * will get overwritten by update_memslots anyway.
+		 */
 		slots = old_memslots;
 	}
 
@@ -868,19 +875,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	if (r)
 		goto out_slots;
 
-	r = -ENOMEM;
-	/*
-	 * We can re-use the old_memslots from above, the only difference
-	 * from the currently installed memslots is the invalid flag.  This
-	 * will get overwritten by update_memslots anyway.
-	 */
-	if (!slots) {
-		slots = kmemdup(kvm->memslots, sizeof(struct kvm_memslots),
-				GFP_KERNEL);
-		if (!slots)
-			goto out_free;
-	}
-
 	/*
 	 * IOMMU mapping:  New slots need to be mapped.  Old slots need to be
 	 * un-mapped and re-mapped if their base changes.  Since base change