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Commit 4b2f1e59 authored by Jim Mattson's avatar Jim Mattson Committed by Peter Zijlstra
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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: 9b545c04 ("perf/x86/kvm: Avoid unnecessary work in guest filtering")
Signed-off-by: default avatarJim Mattson <jmattson@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarPeter Shier <pshier@google.com>
Acked-by: default avatarAndi Kleen <ak@linux.intel.com>
Link: https://lkml.kernel.org/r/20210422001834.1748319-1-jmattson@google.com
parent 9d480158
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