[PATCH 2/2] powerpc/perf: Fix mmcra corruption by bhrb_filter

[Ravi Bangoria]

Consider a scenario where user creates two events:

  1st event:
    attr.sample_type |= PERF_SAMPLE_BRANCH_STACK;
    attr.branch_sample_type = PERF_SAMPLE_BRANCH_ANY;
    fd = perf_event_open(attr, 0, 1, -1, 0);

  This sets cpuhw->bhrb_filter to 0 and returns valid fd.

  2nd event:
    attr.sample_type |= PERF_SAMPLE_BRANCH_STACK;
    attr.branch_sample_type = PERF_SAMPLE_BRANCH_CALL;
    fd = perf_event_open(attr, 0, 1, -1, 0);

  It overrides cpuhw->bhrb_filter to -1 and returns with error.

Now if power_pmu_enable() gets called by any path other than
power_pmu_add(), ppmu->config_bhrb(-1) will set mmcra to -1.

Signed-off-by: Ravi Bangoria <ravi.bango...@linux.ibm.com>
---
 arch/powerpc/perf/core-book3s.c | 6 ++++--
 arch/powerpc/perf/power8-pmu.c  | 3 +++
 arch/powerpc/perf/power9-pmu.c  | 3 +++
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index b0723002a396..8eb5dc5df62b 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1846,6 +1846,7 @@ static int power_pmu_event_init(struct perf_event *event)
        int n;
        int err;
        struct cpu_hw_events *cpuhw;
+       u64 bhrb_filter;
 
        if (!ppmu)
                return -ENOENT;
@@ -1951,13 +1952,14 @@ static int power_pmu_event_init(struct perf_event 
*event)
        err = power_check_constraints(cpuhw, events, cflags, n + 1);
 
        if (has_branch_stack(event)) {
-               cpuhw->bhrb_filter = ppmu->bhrb_filter_map(
+               bhrb_filter = ppmu->bhrb_filter_map(
                                        event->attr.branch_sample_type);
 
-               if (cpuhw->bhrb_filter == -1) {
+               if (bhrb_filter == -1) {
                        put_cpu_var(cpu_hw_events);
                        return -EOPNOTSUPP;
                }
+               cpuhw->bhrb_filter = bhrb_filter;
        }
 
        put_cpu_var(cpu_hw_events);
diff --git a/arch/powerpc/perf/power8-pmu.c b/arch/powerpc/perf/power8-pmu.c
index d12a2db26353..d10feef93b6b 100644
--- a/arch/powerpc/perf/power8-pmu.c
+++ b/arch/powerpc/perf/power8-pmu.c
@@ -29,6 +29,7 @@ enum {
 #define        POWER8_MMCRA_IFM1               0x0000000040000000UL
 #define        POWER8_MMCRA_IFM2               0x0000000080000000UL
 #define        POWER8_MMCRA_IFM3               0x00000000C0000000UL
+#define        POWER8_MMCRA_BHRB_MASK          0x00000000C0000000UL
 
 /*
  * Raw event encoding for PowerISA v2.07 (Power8):
@@ -243,6 +244,8 @@ static u64 power8_bhrb_filter_map(u64 branch_sample_type)
 
 static void power8_config_bhrb(u64 pmu_bhrb_filter)
 {
+       pmu_bhrb_filter &= POWER8_MMCRA_BHRB_MASK;
+
        /* Enable BHRB filter in PMU */
        mtspr(SPRN_MMCRA, (mfspr(SPRN_MMCRA) | pmu_bhrb_filter));
 }
diff --git a/arch/powerpc/perf/power9-pmu.c b/arch/powerpc/perf/power9-pmu.c
index 030544e35959..f3987915cadc 100644
--- a/arch/powerpc/perf/power9-pmu.c
+++ b/arch/powerpc/perf/power9-pmu.c
@@ -92,6 +92,7 @@ enum {
 #define POWER9_MMCRA_IFM1              0x0000000040000000UL
 #define POWER9_MMCRA_IFM2              0x0000000080000000UL
 #define POWER9_MMCRA_IFM3              0x00000000C0000000UL
+#define POWER9_MMCRA_BHRB_MASK         0x00000000C0000000UL
 
 /* Nasty Power9 specific hack */
 #define PVR_POWER9_CUMULUS             0x00002000
@@ -300,6 +301,8 @@ static u64 power9_bhrb_filter_map(u64 branch_sample_type)
 
 static void power9_config_bhrb(u64 pmu_bhrb_filter)
 {
+       pmu_bhrb_filter &= POWER9_MMCRA_BHRB_MASK;
+
        /* Enable BHRB filter in PMU */
        mtspr(SPRN_MMCRA, (mfspr(SPRN_MMCRA) | pmu_bhrb_filter));
 }
-- 
2.20.1