Received-SPF: pass (google.com: domain of linux-kernel+bounces-16067-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
Date: Wed, 3 Jan 2024 14:22:23 -0800
From: "Paul E. McKenney" <paulmck@kernel.org>
To: Like Xu <like.xu@linux.intel.com>, Andi Kleen <ak@linux.intel.com>,
	Kan Liang <kan.liang@linux.intel.com>,
	Luwei Kang <luwei.kang@intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, Breno Leitao <leitao@debian.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Ingo Molnar <mingo@redhat.com>
Subject: [BUG] Guest OSes die simultaneously (bisected)
Message-ID: <3d8f5987-e09c-4dd2-a9c0-8ba22c9e948a@paulmck-laptop>
Reply-To: paulmck@kernel.org
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline

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.

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