[Patch v4 1/5] perf/x86/intel: Improve validation and configuration of ACR masks

[Dapeng Mi <dapeng1.mi@linux.intel.com>]

Currently there are several issues on the user space ACR mask validation
and configuration.
- The validation for user space ACR mask (attr.config2) is incomplete,
  e.g., the ACR mask could include the index which belongs to another
  ACR events group, but it's not validated.
- An early return on an invalid ACR mask caused all subsequent ACR groups
  to be skipped.
- The stale hardware ACR mask (hw.config1) is not cleared before setting
  new hardware ACR mask.

The following changes address all of the above issues.
- Figure out the event index group of an ACR group. Any bits in the
  user-space mask not present in the index group are now dropped.
- Instead of an early return on invalid bits, drop only the invalid
  portions and continue iterating through all ACR events to ensure full
  configuration.
- Explicitly clear the stale hardware ACR mask for each event prior to
  writing the new configuration.

Besides, a non-leader event member of ACR group could be disabled in
theory. This could cause bit-shifting errors in the acr_mask of remaining
group members. But since ACR sampling requires all events to be active,
this should not be a big concern in real use case. Add a "FIXME" comment
to notice this risk.

Cc: stable@vger.kernel.org
Fixes: ec980e4facef ("perf/x86/intel: Support auto counter reload")
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
---

V4: 1) Simplify ACR group indices validation. 2) Add FIXME to notify the
bit-shifting risk of ACR mask if event numbers of ACR group are diabled.

 arch/x86/events/intel/core.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 4768236c054b..ca910e6bfc77 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3332,23 +3332,41 @@ static void intel_pmu_enable_event(struct perf_event *event)
 static void intel_pmu_acr_late_setup(struct cpu_hw_events *cpuc)
 {
 	struct perf_event *event, *leader;
-	int i, j, idx;
+	int i, j, k, bit, idx;
 
+	/*
+	 * FIXME: ACR mask parsing relies on cpuc->event_list[] (active events only).
+	 * Disabling an ACR event causes bit-shifting errors in the acr_mask of
+	 * remaining group members. As ACR sampling requires all events to be active,
+	 * this limitation is acceptable for now. Revisit if independent event toggling
+	 * is required.
+	 */
 	for (i = 0; i < cpuc->n_events; i++) {
 		leader = cpuc->event_list[i];
 		if (!is_acr_event_group(leader))
 			continue;
 
-		/* The ACR events must be contiguous. */
+		/* Find the last event of the ACR group. */
 		for (j = i; j < cpuc->n_events; j++) {
 			event = cpuc->event_list[j];
 			if (event->group_leader != leader->group_leader)
 				break;
-			for_each_set_bit(idx, (unsigned long *)&event->attr.config2, X86_PMC_IDX_MAX) {
-				if (i + idx >= cpuc->n_events ||
-				    !is_acr_event_group(cpuc->event_list[i + idx]))
-					return;
-				__set_bit(cpuc->assign[i + idx], (unsigned long *)&event->hw.config1);
+		}
+
+		/*
+		 * Translate the user-space ACR mask (attr.config2) into the physical
+		 * counter bitmask (hw.config1) for each ACR event in the group.
+		 * NOTE: ACR event contiguity is guaranteed by intel_pmu_hw_config().
+		 */
+		for (k = i; k < j; k++) {
+			event = cpuc->event_list[k];
+			event->hw.config1 = 0;
+			for_each_set_bit(bit, (unsigned long *)&event->attr.config2, X86_PMC_IDX_MAX) {
+				idx = i + bit;
+				/* Event index of ACR group must locate in [i, j). */
+				if (idx >= j || !is_acr_event_group(cpuc->event_list[idx]))
+					continue;
+				__set_bit(cpuc->assign[idx], (unsigned long *)&event->hw.config1);
 			}
 		}
 		i = j - 1;
-- 
2.34.1