libsel4vm: set VM_GUEST_ERROR_EXIT on vCPU index error?

[axel-h]

I wonder, in

seL4_projects_libs/libsel4vm/src/arch/arm/vm.c

Lines 234 to 241 in 9de0630

	tag = seL4_Recv(vm->host_endpoint, &sender_badge);
	label = seL4_MessageInfo_get_label(tag);
	if (sender_badge >= MIN_VCPU_BADGE && sender_badge <= MAX_VCPU_BADGE) {
	seL4_Word vcpu_idx = VCPU_BADGE_IDX(sender_badge);
	if (vcpu_idx >= vm->num_vcpus) {
	ZF_LOGE("Invalid VCPU index. Exiting");
	ret = -1;
	} else {

shouldn't this also set

vm->run.exit_reason = VM_GUEST_ERROR_EXIT;

if vcpu_idx is invalid?

[Ivan-Velickovic]

Is there an instance where exit_reason is actually used? I can only see it being set.

[axel-h]

I though it's part of the API. So the examples should be improved to make use of this - or have a comment that they don't use this because it does not make an difference for the example.

[alisonfel]

I wonder, in

seL4_projects_libs/libsel4vm/src/arch/arm/vm.c

Lines 234 to 241 in 9de0630

	tag = seL4_Recv(vm->host_endpoint, &sender_badge);
	label = seL4_MessageInfo_get_label(tag);
	if (sender_badge >= MIN_VCPU_BADGE && sender_badge <= MAX_VCPU_BADGE) {
	seL4_Word vcpu_idx = VCPU_BADGE_IDX(sender_badge);
	if (vcpu_idx >= vm->num_vcpus) {
	ZF_LOGE("Invalid VCPU index. Exiting");
	ret = -1;
	} else {

shouldn't this also set

vm->run.exit_reason = VM_GUEST_ERROR_EXIT;

if vcpu_idx is invalid?

Yep, vm->run.exit_reason = VM_GUEST_ERROR_EXIT; should be set when the vcpu_idx is invalid. This is likely a small bug, I might've just missed this when refactoring the libraries a few years ago.

[axel-h]

I assume it should also be set here then:

seL4_projects_libs/libsel4vm/src/arch/arm/vm.c

Lines 249 to 255 in 9de0630

	if (vm->run.notification_callback) {
	err = vm->run.notification_callback(vm, sender_badge, tag,
	vm->run.notification_callback_cookie);
	} else {
	ZF_LOGE("Unable to handle VM notification. Exiting");
	err = -1;
	}

[alisonfel]

Hmm, I don't follow? That case should be already handled just below:

seL4_projects_libs/libsel4vm/src/arch/arm/vm.c

Lines 256 to 259 in 9de0630

	if (err) {
	ret = -1;
	vm->run.exit_reason = VM_GUEST_ERROR_EXIT;
	}

[axel-h]

Ah yes, it's set there eventually for all errors.