KVM: s390: Skip gfn/size sanity checks on memslot DELETE or FLAGS_ONLY

Sanity check the hva, gfn, and size of a userspace memory region only if
any of those properties can change, i.e. skip the checks for DELETE and
FLAGS_ONLY.  KVM doesn't allow moving the hva or changing the size, a gfn
change shows up as a MOVE even if flags are being modified, and the
checks are pointless for the DELETE case as userspace_addr and gfn_base
are zeroed by common KVM.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Message-Id: <05430738437ac2c9c7371ac4e11f4a533e1677da.1638817640.git.maciej.szmigiero@oracle.com>

arch/s390/kvm/kvm-s390.c

@@ -5011,7 +5011,14 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
 {
-	gpa_t size = new->npages * PAGE_SIZE;
+	gpa_t size;
+
+	/* When we are protected, we should not change the memory slots */
+	if (kvm_s390_pv_get_handle(kvm))
+		return -EINVAL;
+
+	if (change == KVM_MR_DELETE || change == KVM_MR_FLAGS_ONLY)
+		return 0;
 
 	/* A few sanity checks. We can have memory slots which have to be
 	   located/ended at a segment boundary (1MB). The memory in userland is
@@ -5021,15 +5028,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	if (new->userspace_addr & 0xffffful)
 		return -EINVAL;
 
+	size = new->npages * PAGE_SIZE;
 	if (size & 0xffffful)
 		return -EINVAL;
 
 	if ((new->base_gfn * PAGE_SIZE) + size > kvm->arch.mem_limit)
 		return -EINVAL;
 
-	/* When we are protected, we should not change the memory slots */
-	if (kvm_s390_pv_get_handle(kvm))
-		return -EINVAL;
 	return 0;
 }