powerpc: fix hardware PMU exception bug on PowerVM compatibility mode systems

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

diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
index e745abc..245be4f 100644 (file)
--- a/arch/powerpc/kernel/cputable.c
+++ b/arch/powerpc/kernel/cputable.c
@@ -2193,11 +2193,13 @@ static struct cpu_spec * __init setup_cpu_spec(unsigned long offset,
                 * 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;
                }
        }