lkml.org 
[lkml]   [2021]   [Jul]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [perf] fuzzer triggers unchecked MSR access error: WRMSR to 0x318
On Thu, Jul 29, 2021 at 09:21:01AM -0400, Liang, Kan wrote:
>
>
> On 7/29/2021 5:14 AM, Peter Zijlstra wrote:
> > On Wed, Jul 28, 2021 at 12:49:43PM -0400, Vince Weaver wrote:
> > > [32694.087403] unchecked MSR access error: WRMSR to 0x318 (tried to write 0x0000000000000000) at rIP: 0xffffffff8106f854 (native_write_msr+0x4/0x20)
> > > [32694.101374] Call Trace:
> > > [32694.103974] perf_clear_dirty_counters+0x86/0x100
> >
> > Hmm.. if I read this right that's MSR_ARCH_PERFMON_FIXED_CTR0 + i, given
> > that FIXED_CTR0 is 0x309 that gives i == 15, which is FIXED_BTS.
> >
> > I'm thinking something like this ought to cure things.
> >
> > ---
> > arch/x86/events/core.c | 12 +++++++-----
> > 1 file changed, 7 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> > index 1eb45139fcc6..04edf8017961 100644
> > --- a/arch/x86/events/core.c
> > +++ b/arch/x86/events/core.c
> > @@ -2489,13 +2489,15 @@ void perf_clear_dirty_counters(void)
> > return;
> > for_each_set_bit(i, cpuc->dirty, X86_PMC_IDX_MAX) {
> > - /* Metrics and fake events don't have corresponding HW counters. */
> > - if (is_metric_idx(i) || (i == INTEL_PMC_IDX_FIXED_VLBR))
> > - continue;
> > - else if (i >= INTEL_PMC_IDX_FIXED)
> > + if (i >= INTEL_PMC_IDX_FIXED) {
> > + /* Metrics and fake events don't have corresponding HW counters. */
> > + if ((i - INTEL_PMC_IDX_FIXED) >= x86_pmu.num_counters_fixed)
>
> Yes, the fix is better. My previous implementation tries to pick up all the
> special cases. It's very likely to miss some special cases like FIXED_BTS
> and probably any new fake events added later if there are.
> Thanks for the fix.
>
> The x86_pmu.num_counters_fixed should work well on HSW. But we have hybrid
> machines now. I think we can use
> hybrid(cpuc->pmu, num_counters_fixed) instead, which should be more
> accurate.

Yes, good point. I guess I still need to adjust to the hybrid world.

\
 
 \ /
  Last update: 2021-07-29 17:30    [W:0.083 / U:0.604 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site