[tip: perf/core] perf/amd/ibs: Add ->check_period() callback

[tip-bot2 for Ravi Bangoria]

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

Commit-ID:     1afbdd970f50f2e0431fae26b25d4e54e561fa7f
Gitweb:        https://git.kernel.org/tip/1afbdd970f50f2e0431fae26b25d4e54e561fa7f
Author:        Ravi Bangoria <ravi.bangoria@xxxxxxx>
AuthorDate:    Wed, 15 Jan 2025 05:44:36 
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 03 Feb 2025 11:46:06 +01:00

perf/amd/ibs: Add ->check_period() callback

IBS Fetch and IBS Op PMUs have constraints on sample period. The sample
period is verified at the time of opening an event but not at the ioctl()
interface. Hence, a user can open an event with valid period but change
it later with ioctl(). Add a ->check_period() callback to verify the
period provided at ioctl() is also valid.

Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20250115054438.1021-8-ravi.bangoria@xxxxxxx
---
 arch/x86/events/amd/ibs.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index 7b54b76..aea893a 100644
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -564,6 +564,28 @@ static void perf_ibs_del(struct perf_event *event, int flags)
 
 static void perf_ibs_read(struct perf_event *event) { }
 
+static int perf_ibs_check_period(struct perf_event *event, u64 value)
+{
+	struct perf_ibs *perf_ibs;
+	u64 low_nibble;
+
+	if (event->attr.freq)
+		return 0;
+
+	perf_ibs = container_of(event->pmu, struct perf_ibs, pmu);
+	low_nibble = value & 0xFULL;
+
+	/*
+	 * This contradicts with perf_ibs_init() which allows sample period
+	 * with lower nibble bits set but silently masks them off. Whereas
+	 * this returns error.
+	 */
+	if (low_nibble || value < perf_ibs->min_period)
+		return -EINVAL;
+
+	return 0;
+}
+
 /*
  * We need to initialize with empty group if all attributes in the
  * group are dynamic.
@@ -696,6 +718,7 @@ static struct perf_ibs perf_ibs_fetch = {
 		.start		= perf_ibs_start,
 		.stop		= perf_ibs_stop,
 		.read		= perf_ibs_read,
+		.check_period	= perf_ibs_check_period,
 	},
 	.msr			= MSR_AMD64_IBSFETCHCTL,
 	.config_mask		= IBS_FETCH_MAX_CNT | IBS_FETCH_RAND_EN,
@@ -720,6 +743,7 @@ static struct perf_ibs perf_ibs_op = {
 		.start		= perf_ibs_start,
 		.stop		= perf_ibs_stop,
 		.read		= perf_ibs_read,
+		.check_period	= perf_ibs_check_period,
 	},
 	.msr			= MSR_AMD64_IBSOPCTL,
 	.config_mask		= IBS_OP_MAX_CNT,