Re: [PATCH 1/8] perf/x86/intel: Fix memory corruption

[Stephane Eranian]

On Thu, Mar 21, 2019 at 9:45 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>
> On Thu, 21 Mar 2019, Peter Zijlstra wrote:
> > Subject: perf/x86/intel: Initialize TFA MSR
> >
> > Stephane reported that we don't initialize the TFA MSR, which could lead
> > to trouble if the RESET value is not 0 or on kexec.
>
> That sentence doesn't parse.
>
>   Stephane reported that the TFA MSR is not initialized by the kernel, but
>   the TFA bit could set by firmware or as a leftover from a kexec, which
>   makes the state inconsistent.
>
Correct. This is what I meant.
The issue is what does the kernel guarantee when it boots?

I see:
static bool allow_tsx_force_abort = true;

Therefore you must ensure the MSR is set to reflect that state on boot.
So you have to force it to that value to be in sync which is what your
new patch is doing.

> > Reported-by: Stephane Eranian <eranian@xxxxxxxxxx>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > ---
> >  arch/x86/events/intel/core.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> > index 8baa441d8000..2d3caf2d1384 100644
> > --- a/arch/x86/events/intel/core.c
> > +++ b/arch/x86/events/intel/core.c
> > @@ -3575,6 +3575,12 @@ static void intel_pmu_cpu_starting(int cpu)
> >
> >       cpuc->lbr_sel = NULL;
> >
> > +     if (x86_pmu.flags & PMU_FL_TFA) {
> > +             WARN_ON_ONCE(cpuc->tfa_shadow);
>
> Hmm. I wouldn't warn here as this is a legit state for kexec/kdump and I
> don't think we can figure out whether this comes directly from the
> firmware.
>
> Thanks,
>
>         tglx