[PATCH 5.4 165/168] powerpc: fix hardware PMU exception bug on PowerVM compatibility mode systems

Greg Kroah-Hartman
2020-03-10T13:27:08Z

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
@@ -2193,11 +2193,13 @@ 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;
}
}