Re: [PATCH v9 24/27] virt: gunyah: Add proxy-scheduled vCPUs

Srivatsa Vaddagiri
2023-02-09T10:40:57Z

* Elliot Berman <quic_eberman@quicinc.com> [2023-01-20 14:46:23]:

> +static void gh_handle_mmio_return(struct gunyah_vcpu *vcpu, u64 *state)
> +{
> + if (!vcpu->vcpu_run->mmio.is_write)
> + memcpy(&state[0], vcpu->vcpu_run->mmio.data, vcpu->vcpu_run->mmio.len);

Would be good to do a bound check on length of memcpy I think (in case
vcpu_run_resp->state_data[1] is wrong for example).

> +
> + vcpu->handle_mmio = false;
> + vcpu->vcpu_run->exit_reason = GH_VM_EXIT_UNKNOWN;
> +}
> +

// snip

> +static int gh_vcpu_run(struct gunyah_vcpu *vcpu)
> +{
> + struct gh_hypercall_vcpu_run_resp vcpu_run_resp;
> + u64 state_data[3] = { 0 };
> + int ret = 0;
> +
> + ret = gh_vm_ensure_started(vcpu->ghvm);
> + if (ret)
> + return ret;

Can we move this to VM_START ioctl and avoid this check in fast path? In case VM
is not started, then I think gh_hypercall_vcpu_run() will fail which can catch
erroneous use of VCPU_RUN w/o a preceding VM_START. Alternately we could use a
flag in vcpu struct to check for this case (similar to test for vcpu->rsc
below).

// snip

> + case GH_VCPU_STATE_EXPECTS_WAKEUP:
> + case GH_VCPU_STATE_POWERED_OFF:
> + ret = wait_for_completion_interruptible(&vcpu->ready);

I think we should end this wait in case immediate_exit is set as well.

> +static vm_fault_t gh_vcpu_fault(struct vm_fault *vmf)
> +{
> + struct gunyah_vcpu *vcpu = vmf->vma->vm_file->private_data;
> + struct page *page = NULL;
> +
> + if (vmf->pgoff == 0)
> + page = virt_to_page(vcpu->vcpu_run);
> +
> + get_page(page);

We should avoid get_page in case page is NULL.

> + vmf->page = page;
> + return 0;
> +}
> +
> +static void gunyah_vcpu_unpopulate(struct gunyah_vm_resource_ticket *ticket,
> + struct gunyah_resource *ghrsc)
> +{
> + struct gunyah_vcpu *vcpu = container_of(ticket, struct gunyah_vcpu, ticket);
> +
> + vcpu->vcpu_run->immediate_exit = true;

We should poke the vcpu thread as well so that it can notice this.
Otherwise it can continue to be in gh_hypercall_vcpu_run() or
wait_for_completion_interruptible() for longer time to come.

> + mutex_lock(&vcpu->run_lock);
> + free_irq(vcpu->rsc->irq, vcpu);
> + vcpu->rsc = NULL;
> + mutex_unlock(&vcpu->run_lock);
> +}
> +
> +static long gunyah_vcpu_bind(struct gunyah_vm_function *f)
> +{
> + struct gunyah_vcpu *vcpu;
> + char name[MAX_VCPU_NAME];
> + struct file *file;
> + struct page *page;
> + int fd;
> + long r;
> +
> + if (!gh_api_has_feature(GH_API_FEATURE_VCPU))

We should test for this feature before registering the function? What's
the point in registering a function otherwise if it can't do its work!