Messages in this thread | | | Date | Wed, 21 Apr 2021 19:05:12 -0700 | From | Andi Kleen <> | Subject | Re: [PATCH] perf/x86/kvm: Fix Broadwell Xeon stepping in isolation_ucodes[] |
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On Wed, Apr 21, 2021 at 05:18:34PM -0700, Jim Mattson wrote: > The only stepping of Broadwell Xeon parts is stepping 1. Fix the > relevant isolation_ucodes[] entry, which previously enumerated > stepping 2. > > Although the original commit was characterized as an optimization, it > is also a workaround for a correctness issue. > > If a PMI arrives between kvm's call to perf_guest_get_msrs() and the > subsequent VM-entry, a stale value for the IA32_PEBS_ENABLE MSR may be > restored at the next VM-exit. This is because, unbeknownst to kvm, PMI > throttling may clear bits in the IA32_PEBS_ENABLE MSR. CPUs with "PEBS > isolation" don't suffer from this issue, because perf_guest_get_msrs() > doesn't report the IA32_PEBS_ENABLE value.
Acked-by: Andi Kleen <ak@linux.intel.com>
-Andi
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