[PATCH] drm/amd/amdgpu: Fix iova debugfs for non-iommu case

[Christian König]

Am 19.09.2017 um 19:20 schrieb Tom St Denis:
> On 19/09/17 01:18 PM, Christian König wrote:
>> Am 19.09.2017 um 19:14 schrieb Tom St Denis:
>>> On 19/09/17 01:10 PM, Christian König wrote:
>>>> As far as I know we don't need #ifdefs cause there are dummy 
>>>> functions when IOMMU is not compiled in.
>>>>
>>>> But this patch is a NAK since it circumvents the /dev/mem 
>>>> restriction when IOMMU is disabled and that is not something we can 
>>>> easily allow.
>>>
>>> I raised this objection 24 hours ago and was told to go ahead with 
>>> the read/write methods anyways.
>>>
>>> Short of making a list of mappings/allocations in the ttm layer I 
>>> have no idea how we would track this in the non-iommu case which 
>>> means the entire iova debugfs entry should have been NAK'ed in the 
>>> first place.
>>>
>>> I'm open to suggestions.
>>
>> As long as IOMMU is enabled the entry is perfectly fine, cause only 
>> memory mapped to the IOMMU is accessible to the GPU and so accessible 
>> using the debugfs entry as well.
>
> On devices where there's no translation (e.g. Carrizo) does the iommu 
> layer track mappings?  I'm wondering if on those I could seek outside 
> of boundaries and read system memory anyways.

Why do you think there isn't any translation on CZ? I mean the whole ATC 
thing uses the IOMMU (v2 in this case) on APUs.

>> Only when IOMMU is disabled we can't go this way cause we can't know 
>> which memory is mapped to the driver and which isn't (or could we 
>> somehow track this?).
>>
>> I suggest to not create the file in the first place if IOMMU is 
>> disabled.
>
> I could easily do this (basically check if the domain is not null at 
> debugfs init time).

Yeah, please do this for now.

I mean it would be great to have this interface even with IOMMU 
disabled, but of hand I can't think of a way to allow this.

Christian.

>
> Tom