Re: [PATCH v6 2/3] iommu/arm-smmu-v3: Introduce CFGI/TLBI-repeat workaround infrastructure

[Ashish Mhetre <amhetre@nvidia.com>]

On 7/13/2026 11:54 PM, Nicolin Chen wrote:
> On Mon, Jul 13, 2026 at 11:15:41AM +0000, Ashish Mhetre wrote:
>> Tegra264 SMMU instances need every CFGI/TLBI command sequence issued
>> twice, with the second issue executing only after the first issue's
>> CMD_SYNC has completed:
>>
>>      TLBI/CFGI ... CMD_SYNC TLBI/CFGI ... CMD_SYNC
>>
>> ATC_INV is not affected and must never be doubled.
>>
>> Add arm_smmu_erratum_repeat_tlbi_cfgi_key and an
>> arm_smmu_erratum_cmd_needs_repeating() helper that gates on the static
>> key first and then range-checks the opcode (CFGI_STE .. ATC_INV), so
>> subsequent changes wiring the workaround into the CMDQ submission and
>> iommufd batching paths can share a single predicate.
>>
>> Rename the existing arm_smmu_cmdq_issue_cmdlist() to
>> __arm_smmu_cmdq_issue_cmdlist() and add a thin wrapper that re-issues
>> the same cmdlist a second time when the predicate fires. Register the
>> new condition with arm_smmu_cmdq_batch_force_sync() and add
>> arm_vsmmu_can_batch_cmd() so iommufd batches split at every "needs
>> repeating" transition.
>>
>> No callers enable the static key yet, so there is no functional change.
>> A subsequent change will enable the key on affected instances.
> Maybe add a small note (better in patch-3).
>
> Note: since guest-level VCMDQs issue commands directly to the HW, a guest
> kernel enabling the cmdqv feature on NVIDIA Tegra264 must apply this WAR.

Ack.

>> Suggested-by: Nicolin Chen <nicolinc@nvidia.com>
>> Signed-off-by: Ashish Mhetre <amhetre@nvidia.com>
> Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
>
> Some small issues; please fix:

Sure, will respin v7 fixing these.

>> +static bool arm_vsmmu_can_batch_cmd(struct arm_smmu_device *smmu,
>> +				    struct arm_vsmmu_invalidation_cmd *last,
>> +				    struct arm_vsmmu_invalidation_cmd *next)
> @smmu is unused here.

Ack.

>> 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 dd7475c50afc..eb8374cfce2a 100644
>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>> @@ -42,6 +42,14 @@ MODULE_PARM_DESC(disable_msipolling,
>>   static const struct iommu_ops arm_smmu_ops;
>>   static struct iommu_dirty_ops arm_smmu_dirty_ops;
>>   
>> +/*
>> + * Repeat every {CFGI,TLBI};CMD_SYNC command sequence so that the second
>> + * issue executes only after the first issue's CMD_SYNC has completed.
>> + * Does not apply to ATC_INV. The key is global and is enabled from DT
>> + * probe on affected hardware (currently Tegra264 only).
>> + */
>> +static DEFINE_STATIC_KEY_FALSE(arm_smmu_erratum_repeat_tlbi_cfgi_key);
> Since we defined a static key, it would be better explicitly add:
>
> #include <linux/jump_label.h>

Ack.

>> @@ -860,6 +900,11 @@ static bool arm_smmu_cmdq_batch_force_sync(struct arm_smmu_device *smmu,
>>   	    (smmu->options & ARM_SMMU_OPT_CMDQ_FORCE_SYNC))
>>   		return true;
>>   
>> +	/* See the description at arm_smmu_erratum_repeat_tlbi_cfgi_key */
>> +	if (cmds->num == CMDQ_BATCH_ENTRIES &&
>> +	    arm_smmu_erratum_cmd_needs_repeating(&cmds->cmds[0]))
>> +		return true;
> 	/*
> 	 * See the description at arm_smmu_erratum_repeat_tlbi_cfgi_key. Batches
> 	 * never mix CFGI/TLBI with others, so checking cmds[0] alone is enough.
> 	 */
>
> Nicolin

Ack.

Thanks,
Ashish Mhetre