Re: [BUG] Guest OSes die simultaneously (bisected)

[Paul E. McKenney]

On Wed, Jan 03, 2024 at 02:22:23PM -0800, Paul E. McKenney wrote:
> Hello!
> 
> Since some time between v5.19 and v6.4, long-running rcutorture tests
> would (rarely but intolerably often) have all guests on a given host die
> simultaneously with something like an instruction fault or a segmentation
> violation.
> 
> Each bisection step required 20 hosts running 10 hours each, and
> this eventually fingered commit c59a1f106f5c ("KVM: x86/pmu: Add
> IA32_PEBS_ENABLE MSR emulation for extended PEBS").  Although this commit
> is certainly messing with things that could possibly cause all manner
> of mischief, I don't immediately see a smoking gun.  Except that the
> commit prior to this one is rock solid.
> 
> Just to make things a bit more exciting, bisection in mainline proved
> to be problematic due to bugs of various kinds that hid this one.  I was
> therefore forced to bisect among the commits backported to the internal
> v5.19-based kernel, which fingered the backported version of the patch
> called out above.

Ah, and so why do I believe that this is a problem in mainline rather
than just (say) a backporting mistake?

Because this issue was first located in v6.4, which already has this
commit included.

							Thanx, Paul

> Please note that this is not (yet) an emergency.  I will just continue
> to run rcutorture on v5.19-based hypervisors in the meantime.
> 
> Any suggestions for debugging or fixing?
> 
> 							Thanx, Paul