iommu/amd: serialize sequence allocation under concurrent TLB invalidations

With concurrent TLB invalidations, completion wait randomly gets timed out
because cmd_sem_val was incremented outside the IOMMU spinlock, allowing
CMD_COMPL_WAIT commands to be queued out of sequence and breaking the
ordering assumption in wait_on_sem().
Move the cmd_sem_val increment under iommu->lock so completion sequence
allocation is serialized with command queuing.
And remove the unnecessary return.

Fixes: d2a0cac10597 ("iommu/amd: move wait_on_sem() out of spinlock")

Tested-by: Srikanth Aithal <sraithal@amd.com>
Reported-by: Srikanth Aithal <sraithal@amd.com>
Signed-off-by: Ankit Soni <Ankit.Soni@amd.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

1 files changed, 12 insertions, 6 deletions

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 285ae635c324..58be841d624e 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -1439,6 +1439,12 @@ static int iommu_queue_command(struct amd_iommu *iommu, struct iommu_cmd *cmd)
 	return iommu_queue_command_sync(iommu, cmd, true);
 }
 
+static u64 get_cmdsem_val(struct amd_iommu *iommu)
+{
+	lockdep_assert_held(&iommu->lock);
+	return ++iommu->cmd_sem_val;
+}
+
 /*
  * This function queues a completion wait command into the command
  * buffer of an IOMMU
@@ -1453,11 +1459,11 @@ static int iommu_completion_wait(struct amd_iommu *iommu)
 	if (!iommu->need_sync)
 		return 0;
 
-	data = atomic64_inc_return(&iommu->cmd_sem_val);
-	build_completion_wait(&cmd, iommu, data);
-
 	raw_spin_lock_irqsave(&iommu->lock, flags);
 
+	data = get_cmdsem_val(iommu);
+	build_completion_wait(&cmd, iommu, data);
+
 	ret = __iommu_queue_command_sync(iommu, &cmd, false);
 	raw_spin_unlock_irqrestore(&iommu->lock, flags);
 
@@ -3177,10 +3183,11 @@ static void iommu_flush_irt_and_complete(struct amd_iommu *iommu, u16 devid)
 		return;
 
 	build_inv_irt(&cmd, devid);
-	data = atomic64_inc_return(&iommu->cmd_sem_val);
-	build_completion_wait(&cmd2, iommu, data);
 
 	raw_spin_lock_irqsave(&iommu->lock, flags);
+	data = get_cmdsem_val(iommu);
+	build_completion_wait(&cmd2, iommu, data);
+
 	ret = __iommu_queue_command_sync(iommu, &cmd, true);
 	if (ret)
 		goto out_err;
@@ -3194,7 +3201,6 @@ static void iommu_flush_irt_and_complete(struct amd_iommu *iommu, u16 devid)
 
 out_err:
 	raw_spin_unlock_irqrestore(&iommu->lock, flags);
-	return;
 }
 
 static inline u8 iommu_get_int_tablen(struct iommu_dev_data *dev_data)