iommu/arm-smmu: Disable interrupts whilst holding the cmdq lock

The cmdq lock is taken whenever we issue commands into the command queue,
which can occur in IRQ context (as a result of unmap) or in process
context (as a result of a threaded IRQ handler or device probe).

This can lead to a theoretical deadlock if the interrupt handler
performing the unmap hits whilst the lock is taken, so explicitly use
the {irqsave,irqrestore} spin_lock accessors for the cmdq lock.

Tested-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

drivers/iommu/arm-smmu-v3.c

@@ -893,6 +893,7 @@ static void arm_smmu_cmdq_issue_cmd(struct arm_smmu_device *smmu,
 				    struct arm_smmu_cmdq_ent *ent)
 {
 	u64 cmd[CMDQ_ENT_DWORDS];
+	unsigned long flags;
 	bool wfe = !!(smmu->features & ARM_SMMU_FEAT_SEV);
 	struct arm_smmu_queue *q = &smmu->cmdq.q;
 
@@ -902,7 +903,7 @@ static void arm_smmu_cmdq_issue_cmd(struct arm_smmu_device *smmu,
 		return;
 	}
 
-	spin_lock(&smmu->cmdq.lock);
+	spin_lock_irqsave(&smmu->cmdq.lock, flags);
 	while (queue_insert_raw(q, cmd) == -ENOSPC) {
 		if (queue_poll_cons(q, false, wfe))
 			dev_err_ratelimited(smmu->dev, "CMDQ timeout\n");
@@ -910,7 +911,7 @@ static void arm_smmu_cmdq_issue_cmd(struct arm_smmu_device *smmu,
 
 	if (ent->opcode == CMDQ_OP_CMD_SYNC && queue_poll_cons(q, true, wfe))
 		dev_err_ratelimited(smmu->dev, "CMD_SYNC timeout\n");
-	spin_unlock(&smmu->cmdq.lock);
+	spin_unlock_irqrestore(&smmu->cmdq.lock, flags);
 }
 
 /* Context descriptor manipulation functions */