Subject: Re: [PATCH v2 4/7] iommu/arm-smmu-v3: Mark ATC invalidate timeouts via lockless bitmap

From: Samiullah Khawaja <[email-masked]>
Date: Wed, 18 Mar 2026 22:02:32 +0000

Hi Nicolin,

On Tue, Mar 17, 2026 at 12:15:37PM -0700, Nicolin Chen wrote:
>An ATC invalidation timeout is a fatal error. While the SMMUv3 hardware is
>aware of the timeout via a GERROR interrupt, the driver thread issuing the
>commands lacks a direct mechanism to verify whether its specific batch was
>the cause or not, as polling the CMD_SYNC status doesn't natively return a
>failure code, making it very difficult to coordinate per-device recovery.
>
>Introduce an atc_sync_timeouts bitmap in the cmdq structure to bridge this
>gap. When the ISR detects an ATC timeout, set the bit corresponding to the
>physical CMDQ index of the faulting CMD_SYNC command.
>
>On the issuer side, after polling completes (or times out), test and clear
>its dedicated bit. If set, override any generic timeout, return -ETIMEDOUT
>to trigger device quarantine.
>
>Signed-off-by: Nicolin Chen <[email-masked]>
>---
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  1 +
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 20 +++++++++++++++++++-
> 2 files changed, 20 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
>index 36de2b0b2ebe6..3eb12a34b086a 100644
>--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
>+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
>@@ -633,6 +633,7 @@ struct arm_smmu_cmdq {
> 	atomic_long_t			*valid_map;
> 	atomic_t			owner_prod;
> 	atomic_t			lock;
>+	unsigned long			*atc_sync_timeouts;
> 	bool				(*supports_cmd)(struct arm_smmu_cmdq_ent *ent);
> };
>
>diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>index 01030ffd2fe23..9c8972ebc94f9 100644
>--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>@@ -445,7 +445,10 @@ void __arm_smmu_cmdq_skip_err(struct arm_smmu_device *smmu,
> 		 * at the CMD_SYNC. Attempt to complete other pending commands
> 		 * by repeating the CMD_SYNC, though we might well end up back
> 		 * here since the ATC invalidation may still be pending.
>+		 *
>+		 * Mark the faulty batch in the bitmap for the issuer to match.
> 		 */
>+		set_bit(Q_IDX(&q->llq, cons), cmdq->atc_sync_timeouts);
> 		return;
> 	case CMDQ_ERR_CERROR_ILL_IDX:
> 	default:
>@@ -895,9 +898,19 @@ int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu,
>
> 	/* 5. If we are inserting a CMD_SYNC, we must wait for it to complete */
> 	if (sync) {
>+		u32 sync_prod;
>+
> 		llq.prod = queue_inc_prod_n(&llq, n);
>+		sync_prod = llq.prod;
>+
> 		ret = arm_smmu_cmdq_poll_until_sync(smmu, cmdq, &llq);
>-		if (ret) {
>+		if (test_and_clear_bit(Q_IDX(&llq, sync_prod),
>+				       cmdq->atc_sync_timeouts)) {

This will not be set if a software timeout (1 second) occurs. Do you
know if the ATC timeout of Arm sMMUv3 is less than the software timeout
in the driver?

If not maybe we can handle the software timeout here also as the cmdlist
is already known?

Thanks,
Sami
>+			dev_err_ratelimited(smmu->dev,
>+					    "CMD_SYNC for ATC_INV timeout at prod=0x%08x\n",
>+					    sync_prod);
>+			ret = -ETIMEDOUT;
>+		} else if (ret) {
> 			dev_err_ratelimited(smmu->dev,
> 					    "CMD_SYNC timeout at 0x%08x [hwprod 0x%08x, hwcons 0x%08x]\n",
> 					    llq.prod,
>@@ -4458,6 +4471,11 @@ int arm_smmu_cmdq_init(struct arm_smmu_device *smmu,
> 	if (!cmdq->valid_map)
> 		return -ENOMEM;
>
>+	cmdq->atc_sync_timeouts =
>+		devm_bitmap_zalloc(smmu->dev, nents, GFP_KERNEL);
>+	if (!cmdq->atc_sync_timeouts)
>+		return -ENOMEM;
>+
> 	return 0;
> }
>
>-- 
>2.43.0
>
>