Re: [PATCH v8 2/2] Drivers: hv: Introduce mshv_vtl driver

[Sean Christopherson <seanjc@google.com>]

On Mon, Oct 13, 2025, Naman Jain wrote:
> +static int mshv_vtl_ioctl_return_to_lower_vtl(void)
> +{
> +	preempt_disable();
> +	for (;;) {
> +		u32 cancel;
> +		unsigned long irq_flags;
> +		struct hv_vp_assist_page *hvp;
> +		int ret;
> +
> +		local_irq_save(irq_flags);
> +		cancel = READ_ONCE(mshv_vtl_this_run()->cancel);
> +		if (cancel)
> +			current_thread_info()->flags |= _TIF_SIGPENDING;

There's no need to force SIGPENDING, this code can return directly if cancel is
set[1].  And then you can wait to disable IRQs until after handling pending work,
and thus avoid having to immediately re-enable IRQs[2].

[1] https://lore.kernel.org/all/20250828000156.23389-3-seanjc@google.com
[2] https://lore.kernel.org/all/20250828000156.23389-4-seanjc@google.com

> +
> +		if (unlikely(cancel) || __xfer_to_guest_mode_work_pending()) {
> +			local_irq_restore(irq_flags);
> +			preempt_enable();
> +			ret = xfer_to_guest_mode_handle_work();
> +			if (ret)
> +				return ret;
> +			preempt_disable();
> +			continue;
> +		}
> +
> +		mshv_vtl_return(&mshv_vtl_this_run()->cpu_context);
> +		local_irq_restore(irq_flags);
> +
> +		hvp = hv_vp_assist_page[smp_processor_id()];
> +		this_cpu_inc(num_vtl0_transitions);
> +		switch (hvp->vtl_entry_reason) {
> +		case MSHV_ENTRY_REASON_INTERRUPT:
> +			if (!mshv_vsm_capabilities.intercept_page_available &&
> +			    likely(!mshv_vtl_process_intercept()))
> +				goto done;
> +			break;
> +
> +		case MSHV_ENTRY_REASON_INTERCEPT:
> +			WARN_ON(!mshv_vsm_capabilities.intercept_page_available);
> +			memcpy(mshv_vtl_this_run()->exit_message, hvp->intercept_message,
> +			       sizeof(hvp->intercept_message));
> +			goto done;
> +
> +		default:
> +			panic("unknown entry reason: %d", hvp->vtl_entry_reason);
> +		}
> +	}
> +
> +done:
> +	preempt_enable();
> +
> +	return 0;
> +}