Re: [PATCH v3 3/3] iommu/arm-smmu-v3: Issue CFGI/TLBI twice on Tegra264

[Ashish Mhetre <amhetre@nvidia.com>]

On 6/3/2026 1:52 AM, Will Deacon wrote:
> External email: Use caution opening links or attachments
>
>
> On Mon, Jun 01, 2026 at 10:48:45AM +0000, Ashish Mhetre wrote:
>> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
>> index 1e9f7d2de344..78c96a2b652b 100644
>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
>> @@ -350,6 +350,26 @@ static int arm_vsmmu_convert_user_cmd(struct arm_vsmmu *vsmmu,
>>        return 0;
>>   }
>>
>> +/*
>> + * On Tegra264, arm_smmu_cmdq_issue_cmdlist() doubles every CFGI/TLBI
>> + * submission (see ARM_SMMU_OPT_TLBI_TWICE). The doubling decision is
>> + * taken once per cmdlist based on the first command, so a single
>> + * batch must not mix commands that need doubling with commands that
>> + * do not. Split the iommufd batch whenever the next user command
>> + * crosses that boundary.
>> + */
> Again, I wouldn't bother with this comment. You probably _should_ update
> Documentation/arch/arm64/silicon-errata.rst, however.

Ack, I'll remove this comment and add in Documentation.

>> +static bool arm_vsmmu_can_batch_cmd(struct arm_smmu_device *smmu,
>> +                                 struct arm_vsmmu_invalidation_cmd *last,
>> +                                 struct arm_vsmmu_invalidation_cmd *next)
>> +{
>> +     struct arm_smmu_cmd next_cmd = {
>> +             .data[0] = le64_to_cpu(next->ucmd.cmd[0]),
>> +     };
>> +
>> +     return arm_smmu_cmd_needs_tlbi_twice(smmu, &last->cmd) ==
>> +            arm_smmu_cmd_needs_tlbi_twice(smmu, &next_cmd);
>> +}
>> +
>>   int arm_vsmmu_cache_invalidate(struct iommufd_viommu *viommu,
>>                               struct iommu_user_data_array *array)
>>   {
>> @@ -382,7 +402,8 @@ int arm_vsmmu_cache_invalidate(struct iommufd_viommu *viommu,
>>
>>                /* FIXME work in blocks of CMDQ_BATCH_ENTRIES and copy each block? */
>>                cur++;
>> -             if (cur != end && (cur - last) != CMDQ_BATCH_ENTRIES - 1)
>> +             if (cur != end && (cur - last) != CMDQ_BATCH_ENTRIES - 1 &&
>> +                 arm_vsmmu_can_batch_cmd(smmu, last, cur))
>>                        continue;
> FYI: Sashiko is unhappy with the existing code here, so somebody should
> check that out:
>
> https://sashiko.dev/#/patchset/20260601104845.995005-2-amhetre@nvidia.com
>
>>                /* FIXME always uses the main cmdq rather than trying to group by type */
>> 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 08684bd40a6d..f38c21b56f28 100644
>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>> @@ -698,10 +698,10 @@ static void arm_smmu_cmdq_write_entries(struct arm_smmu_cmdq *cmdq,
>>    *   insert their own list of commands then all of the commands from one
>>    *   CPU will appear before any of the commands from the other CPU.
>>    */
>> -int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu,
>> -                             struct arm_smmu_cmdq *cmdq,
>> -                             struct arm_smmu_cmd *cmds, int n,
>> -                             bool sync)
>> +static int __arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu,
>> +                                      struct arm_smmu_cmdq *cmdq,
>> +                                      struct arm_smmu_cmd *cmds, int n,
>> +                                      bool sync)
>>   {
>>        struct arm_smmu_cmd cmd_sync;
>>        u32 prod;
>> @@ -820,6 +820,26 @@ int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu,
>>        return ret;
>>   }
>>
>> +int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu,
>> +                             struct arm_smmu_cmdq *cmdq,
>> +                             struct arm_smmu_cmd *cmds, int n,
>> +                             bool sync)
>> +{
>> +     int ret = __arm_smmu_cmdq_issue_cmdlist(smmu, cmdq, cmds, n, sync);
>> +
>> +     /*
>> +      * On Tegra264 (see ARM_SMMU_OPT_TLBI_TWICE) re-issue the same
>> +      * cmdlist with another CMD_SYNC to satisfy the erratum.
>> +      * Callers must ensure the batch carries a uniform opcode class
>> +      * so that checking the first command is enough; the iommufd
>> +      * VSMMU path enforces this with arm_vsmmu_can_batch_cmd().
>> +      */
>> +     if (!ret && sync && arm_smmu_cmd_needs_tlbi_twice(smmu, &cmds[0]))
> Can you move the arm_smmu_cmd_... part to the start of the conjunction,
> please? If you make it a static key as I mentioned previously, then
> hopefully that should mean everything else is moved out of line.

Okay, I'll fix this in V4.

>> +             ret = __arm_smmu_cmdq_issue_cmdlist(smmu, cmdq, cmds, n, sync);
> Sashiko is also unhappy here if n == 0 because we probably shouldn't
> be inspecting the command array in that case. Generally, it's a pity
> that we can't handle this all a bit further up in the stack when we know
> exactly what operationg we're trying to perform, but I suppose with all
> the different users of the invalidation commands that's hard to catch in
> one place?
>
>> +
>> +     return ret;
>> +}
>> +
>>   static int arm_smmu_cmdq_issue_cmd_p(struct arm_smmu_device *smmu,
>>                                     struct arm_smmu_cmd *cmd, bool sync)
>>   {
>> @@ -863,6 +883,14 @@ static bool arm_smmu_cmdq_batch_force_sync(struct arm_smmu_device *smmu,
>>            (smmu->options & ARM_SMMU_OPT_CMDQ_FORCE_SYNC))
>>                return true;
>>
>> +     /*
>> +      * Tegra264 erratum (see ARM_SMMU_OPT_TLBI_TWICE). The batch holds
>> +      * a uniform opcode class, so checking the first command is enough.
>> +      */
> Again, please drop the Tegra264 mention and just refer to the option.

Ack.

> Will