On Wed, Jan 22, 2025 at 01:42:28PM +0100, Peter Zijlstra wrote:
> So I'm a little confused, isn't something like this sufficient?
>
> If we hit before schedule(), all just works as expected, if we hit after
> schedule(), the task will already have the TIF flag set, and we'll hit
> the return to user path once it gets scheduled again.
>
> ---
> diff --git a/kernel/task_work.c b/kernel/task_work.c
> index c969f1f26be5..155549c017b2 100644
> --- a/kernel/task_work.c
> +++ b/kernel/task_work.c
> @@ -9,7 +9,12 @@ static struct callback_head work_exited; /* all we need is
> ->next == NULL */
> #ifdef CONFIG_IRQ_WORK
> static void task_work_set_notify_irq(struct irq_work *entry)
> {
> - test_and_set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
> + /*
> + * no-op IPI
> + *
> + * TWA_NMI_CURRENT will already have set the TIF flag, all
> + * this interrupt does it tickle the return-to-user path.
> + */
> }
> static DEFINE_PER_CPU(struct irq_work, irq_work_NMI_resume) =
> IRQ_WORK_INIT_HARD(task_work_set_notify_irq);
> @@ -98,6 +103,7 @@ int task_work_add(struct task_struct *task, struct
> callback_head *work,
> break;
> #ifdef CONFIG_IRQ_WORK
> case TWA_NMI_CURRENT:
> + set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
> irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume));
> break;
> #endif
Yeah, that looks so much better...
The self-IPI is only needed when the NMI happened in user space, right?
Would it make sense to have an optimized version of that?
--
Josh
