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perf/x86/kvm: Fix Broadwell Xeon stepping in isolation_ucodes[]
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. Fixes: 9b545c0 ("perf/x86/kvm: Avoid unnecessary work in guest filtering") Signed-off-by: Jim Mattson <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Reviewed-by: Peter Shier <[email protected]> Acked-by: Andi Kleen <[email protected]> Link: https://lkml.kernel.org/r/[email protected]
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