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

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

[Saket Kumar Bhaskar]

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@linux.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

[tip: perf/core] perf/hw_breakpoint: Return EOPNOTSUPP for unsupported breakpoint type

[tip-bot2 for Saket Kumar Bhaskar]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     21d96cea578f83e43ec9016e5bba8703b290c748
Gitweb:        https://git.kernel.org/tip/21d96cea578f83e43ec9016e5bba8703b290c748
Author:        Saket Kumar Bhaskar <skb99@linux.ibm.com>
AuthorDate:    Mon, 03 Mar 2025 14:54:51 +05:30
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 03 Mar 2025 11:23:15 +01:00

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@linux.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Marco Elver <elver@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: https://lore.kernel.org/r/20250303092451.1862862-1-skb99@linux.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 bc4a610..8ec2cb6 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);

[tip: perf/core] perf/hw_breakpoint: Return EOPNOTSUPP for unsupported breakpoint type

[tip-bot2 for Saket Kumar Bhaskar]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     4118628d0ce005e5651174b9d5fc0209a8d49ee0
Gitweb:        https://git.kernel.org/tip/4118628d0ce005e5651174b9d5fc0209a8d49ee0
Author:        Saket Kumar Bhaskar <skb99@linux.ibm.com>
AuthorDate:    Mon, 03 Mar 2025 14:54:51 +05:30
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 03 Mar 2025 13:24:12 +01:00

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@linux.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Marco Elver <elver@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: https://lore.kernel.org/r/20250303092451.1862862-1-skb99@linux.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 bc4a610..8ec2cb6 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);

Re: [PATCH] perf/hw_breakpoint: Return EOPNOTSUPP for unsupported breakpoint type

[Ian Rogers]

On Mon, Mar 3, 2025 at 1:25 AM Saket Kumar Bhaskar <skb99@linux.ibm.com> wrote:
>
> 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).

Hi Saket,

This looks good to me! Did you happen to run "perf test" as there are
a couple of tests there covering breakpoint behavior and I wonder if
we may need to update them? Particularly there are some comments about
PowerPC just not working:
https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/tests/bp_account.c#n24

Thanks,
Ian

> Signed-off-by: Saket Kumar Bhaskar <skb99@linux.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
>

[tip: perf/core] perf/hw_breakpoint: Return EOPNOTSUPP for unsupported breakpoint type

[tip-bot2 for Saket Kumar Bhaskar]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     061c991697062f3bf87b72ed553d1d33a0e370dd
Gitweb:        https://git.kernel.org/tip/061c991697062f3bf87b72ed553d1d33a0e370dd
Author:        Saket Kumar Bhaskar <skb99@linux.ibm.com>
AuthorDate:    Mon, 03 Mar 2025 14:54:51 +05:30
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 04 Mar 2025 09:42:13 +01:00

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@linux.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Marco Elver <elver@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: https://lore.kernel.org/r/20250303092451.1862862-1-skb99@linux.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 bc4a610..8ec2cb6 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);