On Tue, Sep 08, 2020 at 07:48:58AM +0200, Gerd Hoffmann wrote: > On Mon, Sep 07, 2020 at 03:53:02PM +0200, Daniel Vetter wrote: > > On Mon, Sep 7, 2020 at 1:24 PM Gerd Hoffmann <kraxel@xxxxxxxxxx> wrote: > > > > > > Add drm_device argument to drm_prime_pages_to_sg(), so we can > > > call dma_max_mapping_size() to figure the segment size limit > > > and call into __sg_alloc_table_from_pages() with the correct > > > limit. > > > > > > This fixes virtio-gpu with sev. Possibly it'll fix other bugs > > > too given that drm seems to totaly ignore segment size limits > > > so far ... > > > > > > v2: place max_segment in drm driver not gem object. > > > v3: move max_segment next to the other gem fields. > > > v4: just use dma_max_mapping_size(). > > > > > > Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx> > > > > Uh, are you sure this works in all cases for virtio? > > Sure, I've tested it ;) > > > The comments I've found suggest very much not ... Or is that all very > > old stuff only that no one cares about anymore? > > I think these days it is possible to override dma_ops per device, which > in turn allows virtio to deal with the quirks without the rest of the > kernel knowing about these details. > > I also think virtio-gpu can drop the virtio_has_dma_quirk() checks, just > use the dma api path unconditionally and depend on virtio core having > setup dma_ops in a way that it JustWorks[tm]. I'll look into that next. The comment above vring_use_dma_api() suggests that this has not yet happened, that's why I'm asking. If this has happened then I think it'd be best if you remove that todo entry and update it, as part of the overall series to add dma_max_mapping_size and remove the quirks. Otherwise this all is a bit wtf material :-) -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
