[PATCH v2 4/7] perf/x86/amd/ibs: Don't include randomized bits in get_ibs_op_count()

Kim Phillips
2020-09-08T21:49:01Z

get_ibs_op_count() adds hardware's current count (IbsOpCurCnt) bits
to its count regardless of hardware's valid status.

According to the PPR for AMD Family 17h Model 31h B0 55803 Rev 0.54,
if the counter rolls over, valid status is set, and the lower 7 bits
of IbsOpCurCnt are randomized by hardware.

Don't include those bits in the driver's event count.

Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Fixes: 8b1e13638d46 ("perf/x86-ibs: Fix usage of IBS op current count")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
Cc: Stephane Eranian <eranian@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Cc: x86 <x86@kernel.org>
Cc: stable@vger.kernel.org
---
v2: no changes.

arch/x86/events/amd/ibs.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index 3eb9a55e998c..68776cc291a6 100644
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -334,11 +334,15 @@ static u64 get_ibs_op_count(u64 config)
{
u64 count = 0;

+ /*
+ * If the internal 27-bit counter rolled over, the count is MaxCnt
+ * and the lower 7 bits of CurCnt are randomized.
+ * Otherwise CurCnt has the full 27-bit current counter value.
+ */
if (config & IBS_OP_VAL)
- count += (config & IBS_OP_MAX_CNT) << 4; /* cnt rolled over */
-
- if (ibs_caps & IBS_CAPS_RDWROPCNT)
- count += (config & IBS_OP_CUR_CNT) >> 32;
+ count = (config & IBS_OP_MAX_CNT) << 4;
+ else if (ibs_caps & IBS_CAPS_RDWROPCNT)
+ count = (config & IBS_OP_CUR_CNT) >> 32;

return count;
}
--
2.27.0