[PATCH v9 07/22] perf: arm_pmuv3: Allocate counter indices from high to low

[Colton Lewis <coltonlewis@google.com>]

To minimize collisions between host and guest counters, allocate host
counters from high to low. How the pivot HPMN is defined to partition
the counters gives the guest the low index counters.

Verify both the upper odd counter and lower even counter are present in
cpuc->cntr_mask when allocating 64-bit chained events so that an odd
HPMN boundary does not leak a guest counter into a host chained pair.

Signed-off-by: Colton Lewis <coltonlewis@google.com>
---
 drivers/perf/arm_pmuv3.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
index c15a34684137a..4fcdae8021a56 100644
--- a/drivers/perf/arm_pmuv3.c
+++ b/drivers/perf/arm_pmuv3.c
@@ -958,10 +958,12 @@ static int armv8pmu_get_single_idx(struct pmu_hw_events *cpuc,
 {
 	int idx;
 
-	for_each_set_bit(idx, cpuc->cntr_mask, ARMV8_PMU_MAX_GENERAL_COUNTERS) {
-		if (!test_and_set_bit(idx, cpuc->used_mask))
+	for (idx = ARMV8_PMU_MAX_GENERAL_COUNTERS - 1; idx >= 0; idx--) {
+		if (test_bit(idx, cpuc->cntr_mask) &&
+		    !test_and_set_bit(idx, cpuc->used_mask))
 			return idx;
 	}
+
 	return -EAGAIN;
 }
 
@@ -974,17 +976,22 @@ static int armv8pmu_get_chain_idx(struct pmu_hw_events *cpuc,
 	 * Chaining requires two consecutive event counters, where
 	 * the lower idx must be even.
 	 */
-	for_each_set_bit(idx, cpuc->cntr_mask, ARMV8_PMU_MAX_GENERAL_COUNTERS) {
+	for (idx = ARMV8_PMU_MAX_GENERAL_COUNTERS - 1; idx >= 0; idx--) {
 		if (!(idx & 0x1))
 			continue;
-		if (!test_and_set_bit(idx, cpuc->used_mask)) {
-			/* Check if the preceding even counter is available */
-			if (!test_and_set_bit(idx - 1, cpuc->used_mask))
-				return idx;
-			/* Release the Odd counter */
-			clear_bit(idx, cpuc->used_mask);
+
+		if (test_bit(idx, cpuc->cntr_mask) &&
+		    test_bit(idx - 1, cpuc->cntr_mask)) {
+			if (!test_and_set_bit(idx, cpuc->used_mask)) {
+				/* Check if the preceding even counter is available */
+				if (!test_and_set_bit(idx - 1, cpuc->used_mask))
+					return idx;
+				/* Release the Odd counter */
+				clear_bit(idx, cpuc->used_mask);
+			}
 		}
 	}
+
 	return -EAGAIN;
 }
 
-- 
2.56.0.rc1.310.g51773c2048-goog