Re: [PATCH] x86/pmu: Disable inlining of measure()

Sean Christopherson
2022-10-25T23:12:44Z

On Tue, Oct 25, 2022, Bill Wendling wrote:
> On Wed, Jun 1, 2022 at 10:22 AM Jim Mattson <jmattson@google.com> wrote:
> >
> > On Wed, Jun 1, 2022 at 9:30 AM Bill Wendling <morbo@google.com> wrote:
> > >
> > > From: Bill Wendling <isanbard@gmail.com>
> > >
> > > Clang can be more aggressive at inlining than GCC and will fully inline
> > > calls to measure(). This can mess with the counter overflow check. To
> > > set up the PMC overflow, check_counter_overflow() first records the
> > > number of instructions retired in an invocation of measure() and checks
> > > to see that subsequent calls to measure() retire the same number of
> > > instructions. If inlining occurs, those numbers can be different and the
> > > overflow test fails.
> > >
> > > FAIL: overflow: cntr-0
> > > PASS: overflow: status-0
> > > PASS: overflow: status clear-0
> > > PASS: overflow: irq-0
> > > FAIL: overflow: cntr-1
> > > PASS: overflow: status-1
> > > PASS: overflow: status clear-1
> > > PASS: overflow: irq-1
> > > FAIL: overflow: cntr-2
> > > PASS: overflow: status-2
> > > PASS: overflow: status clear-2
> > > PASS: overflow: irq-2
> > > FAIL: overflow: cntr-3
> > > PASS: overflow: status-3
> > > PASS: overflow: status clear-3
> > > PASS: overflow: irq-3
> > >
> > > Disabling inlining of measure() keeps the assumption that all calls to
> > > measure() retire the same number of instructions.
> > >
> > > Cc: Jim Mattson <jmattson@google.com>
> > > Signed-off-by: Bill Wendling <morbo@google.com>
> > Reviewed-by: Jim Mattson <jmattson@google.com>
>
> Bumping for visibility.

Heh, make sure kvm-unit-tests is in the subject, i.e. [kvm-unit-tests PATCH].
This slipped by on my end because I didn't realize at a quick glance that it was
touching KVM-unit-tests and not kernel code.