Re: [PATCH 01/13] drm/amdgpu: introduce and honour DRM_FORCE_AUTH workaround

["Michel Dänzer" <michel-otUistvHUpPR7s880joybQ@public.gmane.org>]

On 2019-06-21 1:50 p.m., Daniel Vetter wrote:
> On Fri, Jun 21, 2019 at 1:37 PM Christian König
> <ckoenig.leichtzumerken@gmail.com> wrote:
>> Am 21.06.19 um 13:03 schrieb Daniel Vetter:
>>> So if you want to depracate render functionality on primary nodes, you
>>> _have_ to do that hiding in userspace. Or you'll break a lot of
>>> compositors everywhere. Just testing -amdgpu doesn't really prove
>>> anything here. So you won't move the larger ecosystem with this at
>>> all, that ship sailed.
>>
>> So what else can we do? That sounds like you suggest we should
>> completely drop render node functionality.
>>
>> I mean it's not my preferred option, but certainly something that
>> everybody could do.
>>
>> My primary concern is that we somehow need to get rid of thinks like GEM
>> flink and all that other crufty stuff we still have around on the
>> primary node (we should probably make a list of that).
>>
>> Switching everything over to render nodes just sounded like the best
>> alternative so far to archive that.
> 
> tbh I do like that plan too, but it's a lot more work. And I think to
> have any push whatsoever we probably need to roll it out in gbm as a
> hack to keep things going. But probably not enough.
> 
> I also think that at least some compositors will bother to do the
> right thing, and actually bother with render nodes and all that
> correctly. It's just that there's way more which dont.

With amdgpu, we can make userspace always use render nodes for rendering
with changes to libdrm_amdgpu/radeonsi/xf86-video-amdgpu (and maybe some
amdgpu-pro components) only. No GBM/compositor changes needed.


>>> At that point this all feels like a bikeshed, and for a bikeshed I
>>> don't care what the color is we pick, as long as they're all painted
>>> the same.

Then some sheds shouldn't have been re-painted without DRM_AUTH already...


>>> Once we picked a color it's a simple technical matter of how to roll
>>> it out, using Kconfig options, or only enabling on new hw, or "merge
>>> and fix the regressions as they come" or any of the other well proven
>>> paths forward.
>>
>> Yeah, the problem is I don't see an option which currently works for
>> everyone.
>>
>> I absolutely need a grace time of multiple years until we can apply this
>> to amdgpu/radeon.
> 
> Yeah that's what I meant with "pick a color, pick a way to roll it
> out". "enable for new hw, roll out years and years later" is one of
> the options for roll out.

One gotcha being that generic userspace such as the Xorg modesetting
driver may still try to use phased out functionality such as DRI2 with
new hardware.


>> How about this:
>> 1. We keep DRM_AUTH around for amdgpu/radeon for now.
>> 2. We add a Kconfig option to ignore DRM_AUTH, currently default to N.
>> This also works as a workaround for old RADV.
>> 3. We start to work on further removing old cruft from the primary node.
>> Possible the Kconfig option I suggested to disable GEM flink.
> 
> Hm I'm not worried about flink really. It's gem_open which is the
> security gap, and that one has to stay master-only forever.

GEM_OPEN is used by DRI2 clients, it can't be master-only. It's probably
one of the main reasons for the existence of DRM_AUTH.


-- 
Earthling Michel Dänzer               |              https://www.amd.com
Libre software enthusiast             |             Mesa and X developer
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