[PATCH 0/2] perf: complete perf_allow_* trio and use in drm/xe

[PATCH 0/2] perf: complete perf_allow_* trio and use in drm/xe

[John Hubbard]

perf_allow_cpu() and perf_allow_tracepoint() are static inline and
reach into a non-exported sysctl, so modular drivers that want the
same permission model as system-wide perf end up writing partial
copies of this code. Let's instead export these properly so that modules
can call them.

Commit 5e9629d0ae97 ("drivers/perf: arm_spe: Use perf_allow_kernel()
for permissions") already moved perf_allow_kernel() out of line and
exported it. Patch 1 does the same for the other two.

Patch 2 converts drm/xe's OA and EU stall paths to call
perf_allow_cpu(), so xe observation now respects the system
perf_event_paranoid policy and consults the LSM hook. Sites that have
already configured an LSM perf policy or tuned the paranoid sysctl will
now see those settings honored on xe as well.

John Hubbard (2):
  perf/core: out-of-line and export perf_allow_cpu/tracepoint()
  drm/xe: gate observation streams with perf_allow_cpu()

 drivers/gpu/drm/xe/xe_eu_stall.c    |  5 +++--
 drivers/gpu/drm/xe/xe_oa.c          | 25 +++++++++++++---------
 drivers/gpu/drm/xe/xe_observation.c | 32 ++++++++++++++++++++++++-----
 drivers/gpu/drm/xe/xe_observation.h |  3 +--
 include/linux/perf_event.h          | 18 ++--------------
 kernel/events/core.c                | 18 ++++++++++++++++
 6 files changed, 66 insertions(+), 35 deletions(-)


base-commit: b1f7e321a65b3defd5982ead219029ca6d5c8d0f
-- 
2.54.0

[PATCH 1/2] perf/core: out-of-line and export perf_allow_cpu/tracepoint()

[John Hubbard]

These helpers are static inline in <linux/perf_event.h> and reach
into sysctl_perf_event_paranoid and security_perf_event_open(),
neither of which is itself exported. The perf_allow_* trio is
therefore asymmetric: built-in callers can use any of the three, but
modular code can only call perf_allow_kernel().

Move both bodies into kernel/events/core.c next to perf_allow_kernel()
and export them with EXPORT_SYMBOL_GPL, following the shape of
commit 5e9629d0ae97 ("drivers/perf: arm_spe: Use perf_allow_kernel()
for permissions"). Existing in-tree callers live in built-in arch and
tracing code, so the change is invisible to them.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 include/linux/perf_event.h | 18 ++----------------
 kernel/events/core.c       | 18 ++++++++++++++++++
 2 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 48d851fbd8ea..00c4ffe1434d 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1791,22 +1791,8 @@ static inline int perf_is_paranoid(void)
 }
 
 extern int perf_allow_kernel(void);
-
-static inline int perf_allow_cpu(void)
-{
-	if (sysctl_perf_event_paranoid > 0 && !perfmon_capable())
-		return -EACCES;
-
-	return security_perf_event_open(PERF_SECURITY_CPU);
-}
-
-static inline int perf_allow_tracepoint(void)
-{
-	if (sysctl_perf_event_paranoid > -1 && !perfmon_capable())
-		return -EPERM;
-
-	return security_perf_event_open(PERF_SECURITY_TRACEPOINT);
-}
+extern int perf_allow_cpu(void);
+extern int perf_allow_tracepoint(void);
 
 extern int perf_exclude_event(struct perf_event *event, struct pt_regs *regs);
 
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7935d5663944..cb13f3ad11a3 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -14731,6 +14731,24 @@ int perf_allow_kernel(void)
 }
 EXPORT_SYMBOL_GPL(perf_allow_kernel);
 
+int perf_allow_cpu(void)
+{
+	if (sysctl_perf_event_paranoid > 0 && !perfmon_capable())
+		return -EACCES;
+
+	return security_perf_event_open(PERF_SECURITY_CPU);
+}
+EXPORT_SYMBOL_GPL(perf_allow_cpu);
+
+int perf_allow_tracepoint(void)
+{
+	if (sysctl_perf_event_paranoid > -1 && !perfmon_capable())
+		return -EPERM;
+
+	return security_perf_event_open(PERF_SECURITY_TRACEPOINT);
+}
+EXPORT_SYMBOL_GPL(perf_allow_tracepoint);
+
 /*
  * Inherit an event from parent task to child task.
  *
-- 
2.54.0

Claude review: perf/core: out-of-line and export perf_allow_cpu/tracepoint()

[Claude Code Review Bot]

Patch Review

**Correctness: Good.** The moved function bodies are exact copies of the original static inlines:

```c
int perf_allow_cpu(void)
{
	if (sysctl_perf_event_paranoid > 0 && !perfmon_capable())
		return -EACCES;

	return security_perf_event_open(PERF_SECURITY_CPU);
}
EXPORT_SYMBOL_GPL(perf_allow_cpu);
```

This matches the original inline in the header byte-for-byte (minus `static inline`). Same for `perf_allow_tracepoint()`.

**Placement:** The new functions are placed in `kernel/events/core.c` immediately after `perf_allow_kernel()` at line 14731, which is the right location. `EXPORT_SYMBOL_GPL` is the correct export type, matching `perf_allow_kernel()`.

**Header update:** The declarations change from `static inline` with bodies to `extern int` declarations, placed alongside the existing `extern int perf_allow_kernel(void)`. Clean.

**No issues found.** This patch is a mechanical, safe transformation. Existing built-in callers see no functional difference (the function call overhead for these permission checks is negligible). The commit message correctly references the precedent commit 5e9629d0ae97.

---
Generated by Claude Code Patch Reviewer

[PATCH 2/2] drm/xe: gate observation streams with perf_allow_cpu()

[John Hubbard]

xe OA and EU-stall paths open-code a partial copy of the system-wide
perf CPU-event permission check:

    if (xe_observation_paranoid && !perfmon_capable())
            return -EACCES;

This open-coded check skips two things perf_allow_cpu() handles: the
graduated kernel.perf_event_paranoid policy that an administrator
may have tuned, and the security_perf_event_open() LSM hook.

Introduce xe_observation_paranoid_check() to wrap perf_allow_cpu(),
and convert the open-coded sites in xe_oa.c and xe_eu_stall.c. The
dev.xe.observation_paranoid sysctl still acts as an escape hatch
when cleared.

xe observation now consults kernel.perf_event_paranoid and the LSM
perf hook on every open. Sites that have already configured an LSM
perf policy or tuned the paranoid sysctl will see those settings
extend to xe.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/gpu/drm/xe/xe_eu_stall.c    |  5 +++--
 drivers/gpu/drm/xe/xe_oa.c          | 25 +++++++++++++---------
 drivers/gpu/drm/xe/xe_observation.c | 32 ++++++++++++++++++++++++-----
 drivers/gpu/drm/xe/xe_observation.h |  3 +--
 4 files changed, 46 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_eu_stall.c b/drivers/gpu/drm/xe/xe_eu_stall.c
index dddcdd0bb7a3..ede8e3c98b2b 100644
--- a/drivers/gpu/drm/xe/xe_eu_stall.c
+++ b/drivers/gpu/drm/xe/xe_eu_stall.c
@@ -963,9 +963,10 @@ int xe_eu_stall_stream_open(struct drm_device *dev, u64 data, struct drm_file *f
 		return -ENODEV;
 	}
 
-	if (xe_observation_paranoid && !perfmon_capable()) {
+	ret = xe_observation_paranoid_check();
+	if (ret) {
 		drm_dbg(&xe->drm,  "Insufficient privileges for EU stall monitoring\n");
-		return -EACCES;
+		return ret;
 	}
 
 	/* Initialize and set default values */
diff --git a/drivers/gpu/drm/xe/xe_oa.c b/drivers/gpu/drm/xe/xe_oa.c
index 6337e671c97a..f15847be01bc 100644
--- a/drivers/gpu/drm/xe/xe_oa.c
+++ b/drivers/gpu/drm/xe/xe_oa.c
@@ -1676,9 +1676,10 @@ static int xe_oa_mmap(struct file *file, struct vm_area_struct *vma)
 	unsigned long start = vma->vm_start;
 	int i, ret;
 
-	if (xe_observation_paranoid && !perfmon_capable()) {
+	ret = xe_observation_paranoid_check();
+	if (ret) {
 		drm_dbg(&stream->oa->xe->drm, "Insufficient privilege to map OA buffer\n");
-		return -EACCES;
+		return ret;
 	}
 
 	/* Can mmap the entire OA buffer or nothing (no partial OA buffer mmaps) */
@@ -2052,10 +2053,12 @@ int xe_oa_stream_open_ioctl(struct drm_device *dev, u64 data, struct drm_file *f
 		privileged_op = true;
 	}
 
-	if (privileged_op && xe_observation_paranoid && !perfmon_capable()) {
-		drm_dbg(&oa->xe->drm, "Insufficient privileges to open xe OA stream\n");
-		ret = -EACCES;
-		goto err_exec_q;
+	if (privileged_op) {
+		ret = xe_observation_paranoid_check();
+		if (ret) {
+			drm_dbg(&oa->xe->drm, "Insufficient privileges to open xe OA stream\n");
+			goto err_exec_q;
+		}
 	}
 
 	if (!param.exec_q && !param.sample) {
@@ -2334,9 +2337,10 @@ int xe_oa_add_config_ioctl(struct drm_device *dev, u64 data, struct drm_file *fi
 		return -ENODEV;
 	}
 
-	if (xe_observation_paranoid && !perfmon_capable()) {
+	err = xe_observation_paranoid_check();
+	if (err) {
 		drm_dbg(&oa->xe->drm, "Insufficient privileges to add xe OA config\n");
-		return -EACCES;
+		return err;
 	}
 
 	err = copy_from_user(&param, u64_to_user_ptr(data), sizeof(param));
@@ -2436,9 +2440,10 @@ int xe_oa_remove_config_ioctl(struct drm_device *dev, u64 data, struct drm_file
 		return -ENODEV;
 	}
 
-	if (xe_observation_paranoid && !perfmon_capable()) {
+	ret = xe_observation_paranoid_check();
+	if (ret) {
 		drm_dbg(&oa->xe->drm, "Insufficient privileges to remove xe OA config\n");
-		return -EACCES;
+		return ret;
 	}
 
 	ret = get_user(arg, ptr);
diff --git a/drivers/gpu/drm/xe/xe_observation.c b/drivers/gpu/drm/xe/xe_observation.c
index e3f9b546207e..39e05b9131a7 100644
--- a/drivers/gpu/drm/xe/xe_observation.c
+++ b/drivers/gpu/drm/xe/xe_observation.c
@@ -4,6 +4,7 @@
  */
 
 #include <linux/errno.h>
+#include <linux/perf_event.h>
 #include <linux/sysctl.h>
 
 #include <uapi/drm/xe_drm.h>
@@ -12,9 +13,28 @@
 #include "xe_oa.h"
 #include "xe_observation.h"
 
-u32 xe_observation_paranoid = true;
+static u32 xe_observation_paranoid = true;
 static struct ctl_table_header *sysctl_header;
 
+/**
+ * xe_observation_paranoid_check - Gate access to xe observation streams.
+ *
+ * When the xe-specific observation_paranoid sysctl is enabled (the
+ * default), defer to perf_allow_cpu() so that access is governed by the
+ * same policy as system-wide perf CPU events: kernel.perf_event_paranoid
+ * plus the security_perf_event_open() LSM hook. When the sysctl has been
+ * cleared by a privileged user, observation is open to all callers.
+ *
+ * Return: 0 if access is permitted, a negative errno otherwise.
+ */
+int xe_observation_paranoid_check(void)
+{
+	if (!xe_observation_paranoid)
+		return 0;
+
+	return perf_allow_cpu();
+}
+
 static int xe_oa_ioctl(struct drm_device *dev, struct drm_xe_observation_param *arg,
 		       struct drm_file *file)
 {
@@ -83,11 +103,13 @@ static const struct ctl_table observation_ctl_table[] = {
 };
 
 /**
- * xe_observation_sysctl_register - Register xe_observation_paranoid sysctl
+ * xe_observation_sysctl_register - Register the observation_paranoid sysctl
  *
- * Normally only superuser/root can access observation stream
- * data. However, superuser can set xe_observation_paranoid sysctl to 0 to
- * allow non-privileged users to also access observation data.
+ * When dev.xe.observation_paranoid is set (the default), access to
+ * observation streams follows the system-wide perf_allow_cpu() policy:
+ * kernel.perf_event_paranoid plus the security_perf_event_open() LSM
+ * hook. A privileged user can clear the sysctl to bypass that gate and
+ * allow unprivileged access to observation data.
  *
  * Return: always returns 0
  */
diff --git a/drivers/gpu/drm/xe/xe_observation.h b/drivers/gpu/drm/xe/xe_observation.h
index 17816998e966..73a03e03c96a 100644
--- a/drivers/gpu/drm/xe/xe_observation.h
+++ b/drivers/gpu/drm/xe/xe_observation.h
@@ -11,8 +11,7 @@
 struct drm_device;
 struct drm_file;
 
-extern u32 xe_observation_paranoid;
-
+int xe_observation_paranoid_check(void);
 int xe_observation_ioctl(struct drm_device *dev, void *data, struct drm_file *file);
 int xe_observation_sysctl_register(void);
 void xe_observation_sysctl_unregister(void);
-- 
2.54.0

Claude review: drm/xe: gate observation streams with perf_allow_cpu()

[Claude Code Review Bot]

Patch Review

**Design: Good.** The new `xe_observation_paranoid_check()` wrapper is well-designed:

```c
int xe_observation_paranoid_check(void)
{
	if (!xe_observation_paranoid)
		return 0;

	return perf_allow_cpu();
}
```

When the xe-specific sysctl is cleared, observation is open to all — preserving the existing escape hatch. When set (the default), it defers to the system-wide perf policy.

**Making `xe_observation_paranoid` static:** Good call. Since all access is now through `xe_observation_paranoid_check()`, there's no need to export the variable. The sysctl table in the same file still references it directly, which is fine.

**Call-site conversions:** All five sites are correctly converted:
- `xe_eu_stall.c`: 1 site (line 976)
- `xe_oa.c`: 4 sites (mmap, stream open, add config, remove config)

Each now propagates the actual error code from `perf_allow_cpu()` rather than hardcoding `-EACCES`, which is correct behavior.

**Behavioral change — worth documenting to reviewers:**

The old check:
```c
if (xe_observation_paranoid && !perfmon_capable())
    return -EACCES;
```

The new check via `perf_allow_cpu()`:
```c
if (sysctl_perf_event_paranoid > 0 && !perfmon_capable())
    return -EACCES;
return security_perf_event_open(PERF_SECURITY_CPU);
```

This means:
1. If an admin sets `kernel.perf_event_paranoid=0` (or `-1`), non-root users gain xe observation access they previously didn't have (previously, only `perfmon_capable()` was checked). The commit message acknowledges this as the intent.
2. Conversely, LSM policies restricting `PERF_SECURITY_CPU` will now also block xe observation — a tightening that seems correct.

**Potential build issue — missing `CONFIG_PERF_EVENTS` dependency:** The current xe observation code uses `perfmon_capable()` from `<linux/capability.h>`, which is available regardless of `CONFIG_PERF_EVENTS`. After this patch, `xe_observation.c` calls `perf_allow_cpu()`, which is only declared inside `#ifdef CONFIG_PERF_EVENTS` in `<linux/perf_event.h>` and only defined in `kernel/events/core.c` (guarded by the same config). There is no stub in the `#else` block. If someone builds a kernel with `CONFIG_DRM_XE=y` but `CONFIG_PERF_EVENTS=n` (unusual but possible), this will fail to link. Consider adding `depends on PERF_EVENTS` or `select PERF_EVENTS` to `drivers/gpu/drm/xe/Kconfig`, or adding a `#ifndef CONFIG_PERF_EVENTS` fallback that returns `-EACCES` unconditionally.

**Documentation:** The kerneldoc for `xe_observation_paranoid_check()` and the updated sysctl_register doc are clear and accurate.

**Minor nit:** The `xe_oa_stream_open_ioctl` conversion restructures the conditional nicely by pulling `privileged_op` out of the combined `if`:

```c
if (privileged_op) {
    ret = xe_observation_paranoid_check();
    if (ret) {
        ...
        goto err_exec_q;
    }
}
```

This is cleaner than the original three-way `&&`. Good.

---
Generated by Claude Code Patch Reviewer

Claude review: perf: complete perf_allow_* trio and use in drm/xe

[Claude Code Review Bot]

Overall Series Review

Subject: perf: complete perf_allow_* trio and use in drm/xe
Author: John Hubbard <jhubbard@nvidia.com>
Patches: 3
Reviewed: 2026-05-25T21:03:40.409223

---

This is a clean, well-motivated 2-patch series from John Hubbard. Patch 1 promotes `perf_allow_cpu()` and `perf_allow_tracepoint()` from static inlines in `<linux/perf_event.h>` to out-of-line `EXPORT_SYMBOL_GPL` functions in `kernel/events/core.c`, following the existing pattern of `perf_allow_kernel()`. Patch 2 uses the newly-exported `perf_allow_cpu()` in drm/xe to replace open-coded permission checks, aligning xe observation with the system-wide perf security policy.

The series is logically structured, the commit messages are excellent, and the code transformations are straightforward. The behavioral change in patch 2 is intentional and clearly documented: xe observation now respects `kernel.perf_event_paranoid` and the LSM `security_perf_event_open()` hook, rather than doing a simple `perfmon_capable()` check.

There is one potential build issue worth flagging and one minor semantic concern. Overall this looks good to merge.

---
Generated by Claude Code Patch Reviewer