Re: [PATCH 3/8] drm/amdgpu: Implement mmap as GEM object function

[Christian König <christian.koenig@xxxxxxx>]

Am 06.04.21 um 14:52 schrieb Thomas Zimmermann:
> Hi
>
> Am 06.04.21 um 14:42 schrieb Christian König:
> > Hi Thomas,
> >
> > Am 06.04.21 um 13:55 schrieb Thomas Zimmermann:
> > > Hi
> > >
> > > Am 06.04.21 um 12:56 schrieb Christian König:
> > > > > In the end I went with the semantics I found in amdgpu_mmap() and 
> > > > > handled KFD specially. Let me know if this requires to be changed.
> > > >
> > > > Well the question is where is the call to 
> > > > drm_vma_node_verify_access() now? Cause that needs to be skipped 
> > > > for KFD BOs.
> > >
> > > I see. It's now drm_vma_node_is_allowed(); called by drm_gem_mmap(). 
> > > [1] So drm_gem_mmap() cannot be used by amdgpu.
> > >
> > > If I understand the code at [2] correctly, KFD objects don't use the 
> > > GEM ioctl interfaces, but they still use the internal GEM object 
> > > that is part of the TTM BO. In this case, amdgpu could have its own 
> > > version of drm_gem_mmap(), which calls drm_gem_mmap_obj(), [3] which 
> > > in turn handles the mmap details via GEM object functions.
> >
> > Correct, well we could cleanup the KFD to use the GEM functions as well.
>
> The KFD code already calls amdgpu_gem_object_create(). It should have 
> the object-functions pointer set for use with mmap. Not sure what the 
> use of drm_vma_node_is_allowed() would involve.

The KFD allows BOs to be mmaped with different offsets than what's used 
in the DRM node.

So drm_vma_node_is_allowed() would return false as far as I know.

Regards,
Christian.

> Best regards
> Thomas
>
> > Felix what exactly was your objections to using this?
> >
> > Regards,
> > Christian.
> >
> > > drm_gem_prime_mmap() doesn't do any additional verification.
> > >
> > > Best regards
> > > Thomas
> > >
> > > [1] 
> > > https://elixir.bootlin.com/linux/v5.11.11/source/drivers/gpu/drm/drm_gem.c#L1156 
> > >
> > > [2] 
> > > https://elixir.bootlin.com/linux/v5.11.11/source/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c#L1224 
> > >
> > > [3] 
> > > https://elixir.bootlin.com/linux/v5.12-rc6/source/drivers/gpu/drm/drm_gem.c#L1053 
> > >
> > >
> > >
> > > > Regards,
> > > > Christian.
> > > >
> > > > > Best regards
> > > > > Thomas
> > > > >
> > > > > > > -
> > > > > > >   int amdgpu_copy_buffer(struct amdgpu_ring *ring, uint64_t 
> > > > > > > src_offset,
> > > > > > >                  uint64_t dst_offset, uint32_t byte_count,
> > > > > > >                  struct dma_resv *resv,
> > > > > > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h 
> > > > > > > b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
> > > > > > > index dec0db8b0b13..6e51faad7371 100644
> > > > > > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
> > > > > > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
> > > > > > > @@ -146,7 +146,6 @@ int amdgpu_fill_buffer(struct amdgpu_bo *bo,
> > > > > > >               struct dma_resv *resv,
> > > > > > >               struct dma_fence **fence);
> > > > > > > -int amdgpu_mmap(struct file *filp, struct vm_area_struct *vma);
> > > > > > >   int amdgpu_ttm_alloc_gart(struct ttm_buffer_object *bo);
> > > > > > >   int amdgpu_ttm_recover_gart(struct ttm_buffer_object *tbo);
> > > > > > >   uint64_t amdgpu_ttm_domain_start(struct amdgpu_device *adev, 
> > > > > > > uint32_t type);
> > > > > >
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