Re: [PATCH v2 18/24] iommu: Express DMA strictness via the domain type

Lu Baolu
2021-07-29T12:43:46Z

On 2021/7/29 17:36, Robin Murphy wrote:
> On 2021-07-29 08:13, Lu Baolu wrote:
>> Hi Robin,
>>
>> On 7/28/21 11:58 PM, Robin Murphy wrote:
>>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>>> index 982545234cf3..eecb5657de69 100644
>>> --- a/drivers/iommu/iommu.c
>>> +++ b/drivers/iommu/iommu.c
>>> @@ -136,6 +136,9 @@ static int __init iommu_subsys_init(void)
>>>           }
>>>       }
>>> +    if (!iommu_default_passthrough() && !iommu_dma_strict)
>>> +        iommu_def_domain_type = IOMMU_DOMAIN_DMA_FQ;
>>
>> iommu_dma_strict could be changed later by the vendor iommu driver via
>> iommu_set_dma_strict(). This seems not to be the right place to set
>> iommu_def_domain_type.
>
> Ah yes, good catch once again, thanks!
>
> I think this *is* the right place to initially set it to honour the
> command-line option, since that matches what we do for passthrough.
> However also like passthrough we'll need to keep things in sync if it's
> updated later, like this:
>
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 87d7b299436e..593d4555bc57 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -359,6 +359,8 @@ early_param("iommu.strict", iommu_dma_setup);
>  void iommu_set_dma_strict(void)
>  {
>         iommu_dma_strict = true;
> +       if (iommu_def_domain_type == IOMMU_DOMAIN_DMA_FQ)
> +               iommu_def_domain_type = IOMMU_DOMAIN_DMA;
>  }
>
>  static ssize_t iommu_group_attr_show(struct kobject *kobj,
>
>
> Does that seem reasonable? I'm not sure there's any cleaner way to do it
> since we don't want to inadvertently clobber the default type if the
> user has given us something funky like "intel_iommu=strict
> iommu.passthrough=1".

Yeah! It's reasonable as far as I can see.

Best regards,
baolu

>
> Cheers,
> Robin.
>
>>
>>> +
>>>       pr_info("Default domain type: %s %s\n",
>>>           iommu_domain_type_str(iommu_def_domain_type),
>>>           (iommu_cmd_line & IOMMU_CMD_LINE_DMA_API) ?
>>
>> Best regards,
>> baolu