Re: [RFC PATCH 00/13] x86 User Interrupts support

[Sohil Mehta]

On 10/1/2021 1:19 AM, Pavel Machek wrote:
> Hi!

Thank you for reviewing the patches!

> > Instructions
> > ------------
> > senduipi <index> - send a user IPI to a target task based on the UITT index.
> >
> > clui - Mask user interrupts by clearing UIF (User Interrupt Flag).
> >
> > stui - Unmask user interrupts by setting UIF.
> >
> > testui - Test current value of UIF.
> >
> > uiret - return from a user interrupt handler.
>
> Are other CPU vendors allowed to implement compatible instructions?
>
> If not, we should probably have VDSO entries so kernel can abstract
> differences between CPUs.

Yes, we are evaluating VDSO support for this.

> > Untrusted processes
> > -------------------
> > The current implementation expects only trusted and cooperating processes to
> > communicate using user interrupts. Coordination is expected between processes
> > for a connection teardown. In situations where coordination doesn't happen
> > (say, due to abrupt process exit), the kernel would end up keeping shared
> > resources (like UPID) allocated to avoid faults.
>
> Keeping resources allocated after process exit is a no-no.

I meant the resource is still tracked via the shared file descriptor, so 
it will eventually get freed when the FD release happens. I am planning 
to include better documentation on lifetime rules of these shared 
resources next time.

Thanks,
Sohil