[PATCH 1/2] powerpc/perf: Add mtmmcr0(FC) after ppc_set_pmu_inuse(1)

[Madhavan Srinivasan]

pmu_inuse flag is part of lppaca struct which notifies the hypervisor
whether guest/partition is using PMUs. This provides a hint incase of
save/restore of PMU registers. And in power_pmu_enable(), linux sets
the pmu_inuse flag and then updates the PMU registers. Current sequence
in power_pmu_enable() is 1) update pmc_inuse flag 2)update MMCRA, MMCR1,
MMCR0 and so on. But with this sequence, there is a window where when
updating MMCRA, hypersior could load stale value to MMCR0 which could
cause a PMI exception. Patch add a mtmmcr0 with freeze counter bit set
right after updating the pmu_inuse flag to avoid any overflow scenarios.
---
 arch/powerpc/perf/core-book3s.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 3fb6d265ed17..f455e274281a 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1351,6 +1351,7 @@ static void power_pmu_enable(struct pmu *pmu)
 	 * Then unfreeze the events.
 	 */
 	ppc_set_pmu_inuse(1);
+	mtspr(SPRN_MMCR0, MMCR0_FC);
 	mtspr(SPRN_MMCRA, cpuhw->mmcr[2] & ~MMCRA_SAMPLE_ENABLE);
 	mtspr(SPRN_MMCR1, cpuhw->mmcr[1]);
 	mtspr(SPRN_MMCR0, (cpuhw->mmcr[0] & ~(MMCR0_PMC1CE | MMCR0_PMCjCE))
-- 
2.21.0