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From: Madhavan Srinivasan <maddy@linux.ibm.com>
To: mpe@ellerman.id.au
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org
Subject: [PATCH 1/2] powerpc/perf: Add mtmmcr0(FC) after ppc_set_pmu_inuse(1)
Date: Tue, 18 Feb 2020 18:26:30 +0530	[thread overview]
Message-ID: <20200218125631.19692-1-maddy@linux.ibm.com> (raw)

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(+)

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.
 	 */
 	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))
-- 
2.21.1


             reply	other threads:[~2020-02-18 13:03 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-18 12:56 Madhavan Srinivasan [this message]
2020-02-18 12:56 ` [PATCH v2 2/2] powerpc/perf: Check pmus_inuse flag in perf_event_print_debug() Madhavan Srinivasan
  -- strict thread matches above, loose matches on Subject: below --
2019-11-07 13:01 [PATCH 1/2] powerpc/perf: Add mtmmcr0(FC) after ppc_set_pmu_inuse(1) Madhavan Srinivasan

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