[PATCH][SRU Cosmic][SRU Bionic] iommu/arm-smmu-v3: Fix unexpected CMD_SYNC timeout

dann frazier dannf at dannf.org
Tue Mar 5 19:36:54 UTC 2019

From: Zhen Lei <thunder.leizhen at huawei.com>

BugLink: https://bugs.launchpad.net/bugs/1818162

The condition break condition of:

	(int)(VAL - sync_idx) >= 0

in the __arm_smmu_sync_poll_msi() polling loop requires that sync_idx
must be increased monotonically according to the sequence of the CMDs in
the cmdq.

However, since the msidata is populated using atomic_inc_return_relaxed()
before taking the command-queue spinlock, then the following scenario
can occur:

			insert cmd1
insert cmd0
			smmu execute cmd1
smmu execute cmd0
			poll timeout, because msidata=1 is overridden by
			cmd0, that means VAL=0, sync_idx=1.

This is not a functional problem, since the caller will eventually either
timeout or exit due to another CMD_SYNC, however it's clearly not what
the code is supposed to be doing. Fix it, by incrementing the sequence
count with the command-queue lock held, allowing us to drop the atomic
operations altogether.

Signed-off-by: Zhen Lei <thunder.leizhen at huawei.com>
[will: dropped the specialised cmd building routine for now]
Signed-off-by: Will Deacon <will.deacon at arm.com>
(cherry picked from commit 0f02477d16980938a84aba8688a4e3a303306116)
Signed-off-by: dann frazier <dann.frazier at canonical.com>
 drivers/iommu/arm-smmu-v3.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 9c30fb4fccef2..0367432de584d 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -623,7 +623,7 @@ struct arm_smmu_device {
 	int				gerr_irq;
 	int				combined_irq;
-	atomic_t			sync_nr;
+	u32				sync_nr;
 	unsigned long			ias; /* IPA */
 	unsigned long			oas; /* PA */
@@ -1008,14 +1008,13 @@ static int __arm_smmu_cmdq_issue_sync_msi(struct arm_smmu_device *smmu)
 	struct arm_smmu_cmdq_ent ent = {
 		.opcode = CMDQ_OP_CMD_SYNC,
 		.sync	= {
-			.msidata = atomic_inc_return_relaxed(&smmu->sync_nr),
 			.msiaddr = virt_to_phys(&smmu->sync_count),
-	arm_smmu_cmdq_build_cmd(cmd, &ent);
 	spin_lock_irqsave(&smmu->cmdq.lock, flags);
+	ent.sync.msidata = ++smmu->sync_nr;
+	arm_smmu_cmdq_build_cmd(cmd, &ent);
 	arm_smmu_cmdq_insert_cmd(smmu, cmd);
 	spin_unlock_irqrestore(&smmu->cmdq.lock, flags);
@@ -2294,7 +2293,6 @@ static int arm_smmu_init_structures(struct arm_smmu_device *smmu)
 	int ret;
-	atomic_set(&smmu->sync_nr, 0);
 	ret = arm_smmu_init_queues(smmu);
 	if (ret)
 		return ret;

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