Hi Am 20.11.19 um 12:47 schrieb Daniel Vetter: > Hi all, > > I've been looking at dma_buf_v(un)map, with a goal to standardize > locking for at least dynamic dma-buf exporters/importers, most likely > by requiring dma_resv_lock. And I got questions around how this is > supposed to work, since a big chunk of drivers seem to entirely lack > locking around ttm_bo_kmap. Two big ones: > > - ttm_bo_kmap looks at bo->mem to figure out what/where to kmap to get > at that buffer. bo->mem is supposed to be protected with > dma_resv_lock, but at least amgpu/nouveau/radeon/qxl don't grab that > in their prime vmap function. > > - between the vmap and vunmap something needs to make sure the backing > storage doesn't move around. I didn't find that either anywhere, > ttm_bo_kmap simply seems to set up the mapping, leaving locking and > refcounting to callers. You have to pin and unpin storage before and after mapping. > - vram helpers have at least locking, but I'm still missing the > refcounting. vmwgfx doesn't bother with vmap. There's a ref counter for pinning [1] and there's a counter for mapping. [2] Are you looking for something else? Best regards Thomas [1] https://cgit.freedesktop.org/drm/drm-tip/tree/include/drm/drm_gem_vram_helper.h?id=8d3996ceedcd5c64f5a354e9dcc64db4a1f72dd6#n69 [2] https://cgit.freedesktop.org/drm/drm-tip/tree/include/drm/drm_gem_vram_helper.h?id=8d3996ceedcd5c64f5a354e9dcc64db4a1f72dd6#n63 > > What am I missing? > > Thanks, Daniel > -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer
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