Messages in this thread | | | Date | Fri, 28 Feb 2020 10:49:03 +0100 | From | Gerd Hoffmann <> | Subject | Re: [PATCH v5 1/3] drm/shmem: add support for per object caching flags. |
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Hi,
> > Not clue about the others (lima, tiny, panfrost, v3d). Maybe they use > > write-combine just because this is what they got by default from > > drm_gem_mmap_obj(). Maybe they actually need that. Trying to Cc: > > maintainters (and drop stable@).
> > virtio-gpu needs it, otherwise the host can't show the virtual display. > > cirrus bounces everything via blits to vram, so it should be ok without > > decrypted. I guess that implies we should make decrypted configurable. > > Decrypted here is clearly incorrect and violates the SEV spec, regardless of > a config option. > > The only correct way is currently to use dma_alloc_coherent() and > mmap_coherent() to allocate decrypted memory and then use the > pgprot_decrypted flag.
Hmm, virtio-gpu uses the dma api to allow the host access the gem object. So I think I have to correct the statement above, if I understands things correctly the dma api will use (properly allocated) decrypted bounce buffers and the virtio-gpu shmem objects don't need pgprot_decrypted mappings.
That leaves the question what to do about pgprot_writecombine(). Any comments from the driver maintainers (see first paragraph)?
cheers, Gerd
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