[PATCH 2/2] powerpc/perf: Fix the threshold compare group constraint for power9

[Kajol Jain]

Thresh compare bits for a event is used to program thresh compare
field in Monitor Mode Control Register A (MMCRA: 9-18 bits for power9).
When scheduling events as a group, all events in that group should
match value in threshold bits (like thresh compare, thresh control,
thresh select). Otherwise event open for the sibling events should fail.
But in the current code, incase thresh compare bits are not valid,
we are not failing in group_constraint function which can result
in invalid group schduling.

Fix the issue by returning -1 incase event is threshold and threshold
compare value is not valid.

Thresh control bits in the event code is used to program thresh_ctl
field in Monitor Mode Control Register A (MMCRA: 48-55). In below example,
the scheduling of group events PM_MRK_INST_CMPL (873534401e0) and
PM_THRESH_MET (8734340101ec) is expected to fail as both event
request different thresh control bits and invalid thresh compare value.

Result before the patch changes:

[command]# perf stat -e "{r8735340401e0,r8734340101ec}" sleep 1

 Performance counter stats for 'sleep 1':

            11,048      r8735340401e0
             1,967      r8734340101ec

       1.001354036 seconds time elapsed

       0.001421000 seconds user
       0.000000000 seconds sys

Result after the patch changes:

[command]# perf stat -e "{r8735340401e0,r8734340101ec}" sleep 1
Error:
The sys_perf_event_open() syscall returned with 22 (Invalid argument)
for event (r8735340401e0).
/bin/dmesg | grep -i perf may provide additional information.

Fixes: 78a16d9fc1206 ("powerpc/perf: Avoid FAB_*_MATCH checks for power9")
Signed-off-by: Kajol Jain <kjain at linux.ibm.com>
---
 arch/powerpc/perf/isa207-common.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/perf/isa207-common.c b/arch/powerpc/perf/isa207-common.c
index 013b06af6fe6..bb5d64862bc9 100644
--- a/arch/powerpc/perf/isa207-common.c
+++ b/arch/powerpc/perf/isa207-common.c
@@ -508,7 +508,8 @@ int isa207_get_constraint(u64 event, unsigned long *maskp, unsigned long *valp,
 		if (event_is_threshold(event) && is_thresh_cmp_valid(event)) {
 			mask  |= CNST_THRESH_MASK;
 			value |= CNST_THRESH_VAL(event >> EVENT_THRESH_SHIFT);
-		}
+		} else if (event_is_threshold(event))
+			return -1;
 	} else {
 		/*
 		 * Special case for PM_MRK_FAB_RSP_MATCH and PM_MRK_FAB_RSP_MATCH_CYC,
-- 
2.31.1