iommu/arm-smmu-v3: Ratelimit event dump

When a device or driver misbehaves, it is possible to receive DMA fault
events much faster than we can print them out, causing a lock up of the
system and inability to cancel the source of the problem. Ratelimit
printing of events to help recovery.

Tested-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Link: https://lore.kernel.org/r/20210531095648.118282-1-jean-philippe@linaro.org
Signed-off-by: Will Deacon <will@kernel.org>

drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c

@@ -1518,14 +1518,16 @@ static irqreturn_t arm_smmu_evtq_thread(int irq, void *dev)
 	struct arm_smmu_device *smmu = dev;
 	struct arm_smmu_queue *q = &smmu->evtq.q;
 	struct arm_smmu_ll_queue *llq = &q->llq;
+	static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL,
+				      DEFAULT_RATELIMIT_BURST);
 	u64 evt[EVTQ_ENT_DWORDS];
 
 	do {
 		while (!queue_remove_raw(q, evt)) {
 			u8 id = FIELD_GET(EVTQ_0_ID, evt[0]);
 
 			ret = arm_smmu_handle_evt(smmu, evt);
-			if (!ret)
+			if (!ret || !__ratelimit(&rs))
 				continue;
 
 			dev_info(smmu->dev, "event 0x%02x received:\n", id);