Re: [RFC PATCH 11/13] x86/uintr: Introduce uintr_wait() syscall

[Andy Lutomirski]

On Mon, Sep 13, 2021, at 1:01 PM, Sohil Mehta wrote:
> Add a new system call to allow applications to block in the kernel and
> wait for user interrupts.
>

...

>
> When the application makes this syscall the notification vector is
> switched to a new kernel vector. Any new SENDUIPI will invoke the kernel
> interrupt which is then used to wake up the process.

Any new SENDUIPI that happens to hit the target CPU's ucode at a time when the kernel vector is enabled will deliver the interrupt.  Any new SENDUIPI that happens to hit the target CPU's ucode at a time when a different UIPI-using task is running will *not* deliver the interrupt, unless I'm missing some magic.  Which means that wakeups will be missed, which I think makes this whole idea a nonstarter.

Am I missing something?