kvm: selftests: ucall improvements

Make sure we complete the I/O after determining we have a ucall,
which is I/O. Also allow the *uc parameter to optionally be NULL.
It's quite possible that a test case will only care about the
return value, like for example when looping on a check for
UCALL_DONE.

Signed-off-by: Andrew Jones <[e-mail]>
Reviewed-by: Peter Xu <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

tools/testing/selftests/kvm/dirty_log_test.c

···
 	uint64_t *guest_array;
 	uint64_t pages_count = 0;
 	struct kvm_run *run;
-	struct ucall uc;
 
 	run = vcpu_state(vm, VCPU_ID);
 
···
 		/* Let the guest dirty the random pages */
 		ret = _vcpu_run(vm, VCPU_ID);
 		TEST_ASSERT(ret == 0, "vcpu_run failed: %d\n", ret);
-		if (get_ucall(vm, VCPU_ID, &uc) == UCALL_SYNC) {
+		if (get_ucall(vm, VCPU_ID, NULL) == UCALL_SYNC) {
 			pages_count += TEST_PAGES_PER_LOOP;
 			generate_random_array(guest_array, TEST_PAGES_PER_LOOP);
 		} else {

tools/testing/selftests/kvm/lib/ucall.c

···
 uint64_t get_ucall(struct kvm_vm *vm, uint32_t vcpu_id, struct ucall *uc)
 {
 	struct kvm_run *run = vcpu_state(vm, vcpu_id);
-
-	memset(uc, 0, sizeof(*uc));
+	struct ucall ucall = {};
+	bool got_ucall = false;
 
 #ifdef __x86_64__
 	if (ucall_type == UCALL_PIO && run->exit_reason == KVM_EXIT_IO &&
 	    run->io.port == UCALL_PIO_PORT) {
 		struct kvm_regs regs;
 		vcpu_regs_get(vm, vcpu_id, &regs);
-		memcpy(uc, addr_gva2hva(vm, (vm_vaddr_t)regs.rdi), sizeof(*uc));
-		return uc->cmd;
+		memcpy(&ucall, addr_gva2hva(vm, (vm_vaddr_t)regs.rdi), sizeof(ucall));
+		got_ucall = true;
 	}
 #endif
 	if (ucall_type == UCALL_MMIO && run->exit_reason == KVM_EXIT_MMIO &&
···
 		TEST_ASSERT(run->mmio.is_write && run->mmio.len == 8,
 			    "Unexpected ucall exit mmio address access");
 		memcpy(&gva, run->mmio.data, sizeof(gva));
-		memcpy(uc, addr_gva2hva(vm, gva), sizeof(*uc));
+		memcpy(&ucall, addr_gva2hva(vm, gva), sizeof(ucall));
+		got_ucall = true;
 	}
 
-	return uc->cmd;
+	if (got_ucall) {
+		vcpu_run_complete_io(vm, vcpu_id);
+		if (uc)
+			memcpy(uc, &ucall, sizeof(ucall));
+	}
+
+	return ucall.cmd;
 }