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

From: Lu Baolu <baolu.lu@linux.intel.com>
To: Robin Murphy <robin.murphy@arm.com>, joro@8bytes.org, will@kernel.org
Cc: baolu.lu@linux.intel.com, iommu@lists.linux-foundation.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, suravee.suthikulpanit@amd.com,
	john.garry@huawei.com, dianders@chromium.org
Subject: Re: [PATCH v2 18/24] iommu: Express DMA strictness via the domain type
Date: Fri, 30 Jul 2021 14:09:54 +0800	[thread overview]
Message-ID: <f53f2cda-c219-ec61-7698-7efbcaf48ac9@linux.intel.com> (raw)
In-Reply-To: <f2858a7f-e665-ff6a-38d6-b9d591287fac@arm.com>

On 7/29/21 5:36 PM, 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".
> 
> 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

With above fixed,

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>

Best regards,
baolu

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