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    Subject[PATCH 4.19 82/86] powerpc: fix hardware PMU exception bug on PowerVM compatibility mode systems
    Date
    From: Desnes A. Nunes do Rosario <desnesn@linux.ibm.com>

    commit fc37a1632d40c80c067eb1bc235139f5867a2667 upstream.

    PowerVM systems running compatibility mode on a few Power8 revisions are
    still vulnerable to the hardware defect that loses PMU exceptions arriving
    prior to a context switch.

    The software fix for this issue is enabled through the CPU_FTR_PMAO_BUG
    cpu_feature bit, nevertheless this bit also needs to be set for PowerVM
    compatibility mode systems.

    Fixes: 68f2f0d431d9ea4 ("powerpc: Add a cpu feature CPU_FTR_PMAO_BUG")
    Signed-off-by: Desnes A. Nunes do Rosario <desnesn@linux.ibm.com>
    Reviewed-by: Leonardo Bras <leonardo@linux.ibm.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/20200227134715.9715-1-desnesn@linux.ibm.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/powerpc/kernel/cputable.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    --- a/arch/powerpc/kernel/cputable.c
    +++ b/arch/powerpc/kernel/cputable.c
    @@ -2188,11 +2188,13 @@ static struct cpu_spec * __init setup_cp
    * oprofile_cpu_type already has a value, then we are
    * possibly overriding a real PVR with a logical one,
    * and, in that case, keep the current value for
    - * oprofile_cpu_type.
    + * oprofile_cpu_type. Futhermore, let's ensure that the
    + * fix for the PMAO bug is enabled on compatibility mode.
    */
    if (old.oprofile_cpu_type != NULL) {
    t->oprofile_cpu_type = old.oprofile_cpu_type;
    t->oprofile_type = old.oprofile_type;
    + t->cpu_features |= old.cpu_features & CPU_FTR_PMAO_BUG;
    }
    }


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