Messages in this thread | | | Subject | Re: [perf] fuzzer triggers unchecked MSR access error: WRMSR to 0x318 | From | "Liang, Kan" <> | Date | Thu, 29 Jul 2021 09:21:01 -0400 |
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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.
Thanks, Kan
> + continue; > + > wrmsrl(MSR_ARCH_PERFMON_FIXED_CTR0 + (i - INTEL_PMC_IDX_FIXED), 0); > - else > + } else { > wrmsrl(x86_pmu_event_addr(i), 0); > + } > } > > bitmap_zero(cpuc->dirty, X86_PMC_IDX_MAX); >
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