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12cf826bf1
Allow UM to bind sparsely populated memory regions by cyclically mapping virtual ranges over a kernel-allocated dummy BO. This alternative is preferable to the old method of handling sparseness in the UMD, because it relied on the creation of a buffer object to the same end, despite the fact Vulkan sparse resources don't need to be backed by a driver BO. The choice of backing sparsely-bound regions with a Panthor BO was made so as to profit from the existing shrinker reclaim code. That way no special treatment must be given to the dummy sparse BOs when reclaiming memory, as would be the case if we had chosen a raw kernel page implementation. A new dummy BO is allocated per open file context, because even though the Vulkan spec mandates that writes into sparsely bound regions must be discarded, our implementation is still a workaround over the fact Mali CSF GPUs cannot support this behaviour on the hardware level, so writes still make it into the backing BO. If we had a global one, then it could be a venue for information leaks between file contexts, which should never happen in DRM. As a side note, care was put to adjust dummy BO offsets for sparse mappings so that all addresses in the new VA are mapped aligned against it. Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com> Reviewed-by: Steven Price <steven.price@arm.com> Link: https://patch.msgid.link/20260522185206.2798288-6-adrian.larumbe@collabora.com Signed-off-by: Steven Price <steven.price@arm.com>