[PATCH v2] lib: sbi: pmu: Return SBI_EINVAL if cidx_mask is 0 in ctr_cfg_match

[James Raphael Tiovalen]

Currently, when configuring a matching programmable HPM counter with
Sscofpmf being present, cidx_base > 2, and cidx_mask == 0 to monitor
either the CPU_CYCLES or INSTRUCTIONS hardware event, ctr_cfg_match will
succeed but it will configure the corresponding fixed counter instead of
the counter specified by the cidx_base parameter.

During counter configuration, the following issues may arise:
- If the CLEAR_VALUE flag is set, the corresponding fixed counter will
be reset, which could be considered unexpected behavior.

- If the AUTO_START flag is set, ctr_start_hw will silently start the
fixed counter, even though it has already started. From the supervisor's
perspective, nothing has changed, which could be confusing. The
supervisor will not see the SBI_ERR_ALREADY_STARTED error code since
ctr_cfg_match does not return the error code of ctr_start_hw.

The only way to detect these issues is to check the counter_idx return
value of ctr_cfg_match and compare it with cidx_base.

Fix these issues by returning the SBI_ERR_INVALID_PARAM error code if
the cidx_mask parameter value being passed in is 0 since an invalid
parameter should not lead to a successful ctr_cfg_match but with
unexpected side effects. This also aligns OpenSBI's behavior with KVM's.

Signed-off-by: James Raphael Tiovalen <jamestiotio at gmail.com>
---
 lib/sbi/sbi_pmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/sbi/sbi_pmu.c b/lib/sbi/sbi_pmu.c
index 5983a78..62ce770 100644
--- a/lib/sbi/sbi_pmu.c
+++ b/lib/sbi/sbi_pmu.c
@@ -840,7 +840,7 @@ int sbi_pmu_ctr_cfg_match(unsigned long cidx_base, unsigned long cidx_mask,
 	u32 event_code;
 
 	/* Do a basic sanity check of counter base & mask */
-	if ((cidx_base + sbi_fls(cidx_mask)) >= total_ctrs)
+	if (!cidx_mask || ((cidx_base + sbi_fls(cidx_mask)) >= total_ctrs))
 		return SBI_EINVAL;
 
 	event_type = pmu_event_validate(phs, event_idx, event_data);
-- 
2.43.0