KVM: set_memory_region: Refactor prepare_memory_region()

This patch drops the parameter old, a copy of the old memory slot, and
adds a new parameter named change to know the change being requested.

This not only cleans up the code but also removes extra copying of the
memory slot structure.

Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 26216bb..7198234 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6906,23 +6906,21 @@
 
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				struct kvm_memory_slot *memslot,
-				struct kvm_memory_slot old,
-				struct kvm_userspace_memory_region *mem)
+				struct kvm_userspace_memory_region *mem,
+				enum kvm_mr_change change)
 {
-	int npages = memslot->npages;
-
 	/*
 	 * Only private memory slots need to be mapped here since
 	 * KVM_SET_MEMORY_REGION ioctl is no longer supported.
 	 */
-	if ((memslot->id >= KVM_USER_MEM_SLOTS) && npages && !old.npages) {
+	if ((memslot->id >= KVM_USER_MEM_SLOTS) && (change == KVM_MR_CREATE)) {
 		unsigned long userspace_addr;
 
 		/*
 		 * MAP_SHARED to prevent internal slot pages from being moved
 		 * by fork()/COW.
 		 */
-		userspace_addr = vm_mmap(NULL, 0, npages * PAGE_SIZE,
+		userspace_addr = vm_mmap(NULL, 0, memslot->npages * PAGE_SIZE,
 					 PROT_READ | PROT_WRITE,
 					 MAP_SHARED | MAP_ANONYMOUS, 0);