linux-kernel - [PATCH] iommu/amd: serialize sequence allocation under concurrent TLB invalidations

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Message-ID: <abcfda19c05becb988ede3a1a0ba6d87161943bf.1768899638.git.Ankit.Soni@amd.com>
Date: Tue, 20 Jan 2026 09:05:07 +0000
From: Ankit Soni <Ankit.Soni@....com>
To: <iommu@...ts.linux.dev>
CC: <vasant.hegde@....com>, <suravee.suthikulpanit@....com>,
	<joro@...tes.org>, <will@...nel.org>, <robin.murphy@....com>,
	<linux-kernel@...r.kernel.org>, <Srikanth.Aithal@....com>
Subject: [PATCH] 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@....com>
Reported-by: Srikanth Aithal <sraithal@....com>
Signed-off-by: Ankit Soni <Ankit.Soni@....com>
---
 drivers/iommu/amd/iommu.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index d7f457338de7..593fb879b7b0 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -1422,6 +1422,12 @@ 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 atomic64_inc_return(&iommu->cmd_sem_val);
+}
+
 /*
  * This function queues a completion wait command into the command
  * buffer of an IOMMU
@@ -1436,11 +1442,11 @@ 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);
 
@@ -3119,10 +3125,11 @@ 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;
@@ -3136,7 +3143,6 @@ 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)
-- 
2.43.0