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Subject: Re: [PATCH v2 18/24] iommu: Express DMA strictness via the domain
 type
To:     Robin Murphy <robin.murphy@arm.com>, joro@8bytes.org,
        will@kernel.org
References: <cover.1627468308.git.robin.murphy@arm.com>
 <50bee17e9248ccfccb33a10238210d4ff4f4cf4d.1627468309.git.robin.murphy@arm.com>
 <b479f1f9-ecf2-2798-2df8-ae3d4c06bc63@linux.intel.com>
 <f2858a7f-e665-ff6a-38d6-b9d591287fac@arm.com>
From:   Lu Baolu <baolu.lu@linux.intel.com>
Message-ID: <b5167dc8-3b04-f65a-dd69-d338fda341f1@linux.intel.com>
Date:   Thu, 29 Jul 2021 20:42:01 +0800
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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