linux-kernel - [PATCH] perf/hw_breakpoint: Return EOPNOTSUPP for unsupported breakpoint type

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Message-ID: <20250303092451.1862862-1-skb99@linux.ibm.com>
Date: Mon,  3 Mar 2025 14:54:51 +0530
From: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
To: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: peterz@...radead.org, mingo@...hat.com, namhyung@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
        kan.liang@...ux.intel.com, hbathini@...ux.ibm.com,
        atrajeev@...ux.vnet.ibm.com
Subject: [PATCH] perf/hw_breakpoint: Return EOPNOTSUPP for unsupported breakpoint type

Currently, __reserve_bp_slot() returns -ENOSPC for unsupported
breakpoint types on the architecture. For example, powerpc
does not support hardware instruction breakpoints. This causes
the perf_skip BPF selftest to fail, as neither ENOENT nor
EOPNOTSUPP is returned by perf_event_open for unsupported
breakpoint types. As a result, the test that should be skipped
for this arch is not correctly identified.

To resolve this, hw_breakpoint_event_init() should exit early by
checking for unsupported breakpoint types using
hw_breakpoint_slots_cached() and return the appropriate error
(-EOPNOTSUPP).

Signed-off-by: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
---
 kernel/events/hw_breakpoint.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index bc4a61029b6d..8ec2cb688903 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -950,9 +950,10 @@ static int hw_breakpoint_event_init(struct perf_event *bp)
 		return -ENOENT;
 
 	/*
-	 * no branch sampling for breakpoint events
+	 * Check if breakpoint type is supported before proceeding.
+	 * Also, no branch sampling for breakpoint events.
 	 */
-	if (has_branch_stack(bp))
+	if (!hw_breakpoint_slots_cached(find_slot_idx(bp->attr.bp_type)) || has_branch_stack(bp))
 		return -EOPNOTSUPP;
 
 	err = register_perf_hw_breakpoint(bp);
-- 
2.43.5