On Mon, Feb 01, 2021 at 10:58:12AM -0800, Luck, Tony wrote:
> On Thu, Jan 28, 2021 at 06:57:35PM +0100, Borislav Petkov wrote:
> > Crazy idea: if you still can reproduce on -rc3, you could bisect: i.e.,
> > if you apply the patch on -rc3 and it explodes and if you apply the same
> > patch on -rc5 and it works, then that could be a start... Yeah, don't
> > have a better idea here. :-\
>
> I tried reporoducing (applied the original patch I posted back to -rc3) and
> the same issue stubbornly refused to show up again.
>
> But I did hit something with the same signature (overflow bit set in
> bank 1) while running my futex test (which has two processes mapping
> the poison page). This time I *do* understand what happened. The test
> failed when the two processes were running on the two hyperhtreads of
> the same core. Seeing overflow in this case is understandable because
> bank 1 MSRs on my test machine are shared between the HT threads. When
> I run the test again using taskset(1) to only allowing running on
> thread 0 of each core, it keeps going for hunderds of iterations.
>
> I'm not sure I can stitch together how this overflow also happened for
> my single process test. Maybe a migration from one HT thread to the
> other at an awkward moment?
Sounds plausible.
And the much more important question is, what is the code supposed to
do when that overflow *actually* happens in real life? Because IINM,
an overflow condition on the same page would mean killing the task to
contain the error and not killing the machine...
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
