[PATCH 7/8] perf/amd/ibs: Add ->check_period() callback

[Ravi Bangoria]

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>
---
 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 e7522ba45a7e..33728ed6d7a6 100644
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -551,6 +551,28 @@ 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.
@@ -676,6 +698,7 @@ 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,
 		.capabilities	= PERF_PMU_CAP_NO_EXCLUDE,
 	},
 	.msr			= MSR_AMD64_IBSFETCHCTL,
@@ -701,6 +724,7 @@ 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,
 		.capabilities	= PERF_PMU_CAP_NO_EXCLUDE,
 	},
 	.msr			= MSR_AMD64_IBSOPCTL,
-- 
2.46.2