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    Subject[PATCH 5.4 07/20] perf/x86/kvm: Fix Broadwell Xeon stepping in isolation_ucodes[]
    Date
    From: Jim Mattson <jmattson@google.com>

    [ Upstream commit 4b2f1e59229b9da319d358828cdfa4ddbc140769 ]

    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: 9b545c04abd4f ("perf/x86/kvm: Avoid unnecessary work in guest filtering")
    Signed-off-by: Jim Mattson <jmattson@google.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Reviewed-by: Peter Shier <pshier@google.com>
    Acked-by: Andi Kleen <ak@linux.intel.com>
    Link: https://lkml.kernel.org/r/20210422001834.1748319-1-jmattson@google.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/events/intel/core.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
    index 90760393a964..9cb3266e148d 100644
    --- a/arch/x86/events/intel/core.c
    +++ b/arch/x86/events/intel/core.c
    @@ -3999,7 +3999,7 @@ static const struct x86_cpu_desc isolation_ucodes[] = {
    INTEL_CPU_DESC(INTEL_FAM6_BROADWELL_D, 3, 0x07000009),
    INTEL_CPU_DESC(INTEL_FAM6_BROADWELL_D, 4, 0x0f000009),
    INTEL_CPU_DESC(INTEL_FAM6_BROADWELL_D, 5, 0x0e000002),
    - INTEL_CPU_DESC(INTEL_FAM6_BROADWELL_X, 2, 0x0b000014),
    + INTEL_CPU_DESC(INTEL_FAM6_BROADWELL_X, 1, 0x0b000014),
    INTEL_CPU_DESC(INTEL_FAM6_SKYLAKE_X, 3, 0x00000021),
    INTEL_CPU_DESC(INTEL_FAM6_SKYLAKE_X, 4, 0x00000000),
    INTEL_CPU_DESC(INTEL_FAM6_SKYLAKE_X, 5, 0x00000000),
    --
    2.30.2


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