Re: [PATCH v4 00/13] "Task_isolation" mode

Peter Zijlstra
2020-07-23T15:49:46Z

On Thu, Jul 23, 2020 at 03:18:42PM +0000, Alex Belits wrote:
> On Thu, 2020-07-23 at 15:17 +0200, Thomas Gleixner wrote:
> >
> > Without going into details of the individual patches, let me give you a
> > high level view of this series:
> >
> > 1) Entry code handling:
> >
> > That's completely broken vs. the careful ordering and instrumentation
> > protection of the entry code. You can't just slap stuff randomly
> > into places which you think are safe w/o actually trying to understand
> > why this code is ordered in the way it is.
> >
> > This clearly was never built and tested with any of the relevant
> > debug options enabled. Both build and boot would have told you.
>
> This is intended to avoid a race condition when entry or exit from isolation
> happens at the same time as an event that requires synchronization. The idea
> is, it is possible to insulate the core from all events while it is running
> isolated task in userspace, it will receive those calls normally after
> breaking isolation and entering kernel, and it will synchronize itself on
> kernel entry.

'What does noinstr mean? and why do we have it" -- don't dare touch the
entry code until you can answer that.