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

Message ID 20200218125631.19692-1-maddy@linux.ibm.com (mailing list archive)
State New
Headers show
Series [1/2] powerpc/perf: Add mtmmcr0(FC) after ppc_set_pmu_inuse(1) | expand


Context Check Description
snowpatch_ozlabs/apply_patch success Successfully applied on branch powerpc/merge (a5bc6e124219546a81ce334dc9b16483d55e9abf)
snowpatch_ozlabs/checkpatch success total: 0 errors, 0 warnings, 0 checks, 7 lines checked
snowpatch_ozlabs/needsstable success Patch has no Fixes tags

Commit Message

Madhavan Srinivasan Feb. 18, 2020, 12:56 p.m. UTC
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.

Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
 arch/powerpc/perf/core-book3s.c | 1 +
 1 file changed, 1 insertion(+)
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diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index a934e8c8a9b8..6e35bf9ff80a 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1343,6 +1343,7 @@  static void power_pmu_enable(struct pmu *pmu)
 	 * Then unfreeze the events.
+	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))