On Thu, Mar 05, 2015 at 01:01:21PM +0000, Chris Wilson wrote: > On Thu, Mar 05, 2015 at 01:52:51PM +0100, Daniel Vetter wrote: > > On Thu, Mar 05, 2015 at 02:56:52AM +0000, Song, Ruiling wrote: > > > Hi Daniel, > > > > > > OpenCL language support NULL pointer, using zero as the NULL pointer is > > > the obvious way. That is zero will be treated as invalid address. Then > > > it requires drm won't allocate zero to drm buffer. And David in CC > > > list has help us make a patch, please see attached. The logic is only > > > for ppgtt, and he said zero offset is used under ggtt. My question is > > > what is offset zero used under ggtt? Will it make sure zero is not > > > allocatable to drm buffer object? > > > > The code in i915_gem_execbuf.c already supports an optional bias to avoid > > putting a buffer into the first few kb. See __EXEC_OBJECT_NEEDS_BIAS. I > > suggest you expose this to userspace, which also address your issue that > > you didn't add an abi revision flag. > > A better API would be to allow userspace to request a buffer to place at > a specific point in the VM and fail if that is not possible aka > soft-pinning. Then OCL could assign a bo to offset 0 and detect writes > to the NULL address if it so desired. With full-ppgtt, userspace can be > sure of being able to evict any location in its VM and so also allows > graceful detection of scenarios under which it cannot provide the NULL > address safety feature (and opt not to run, or just bury its head in the > sand). I recommended exposing the PIN_BIAS since that will work without full ppgtt too. And yeah for full ppgtt we could just use svm where userspace controls the address, but since that's still a bit out we might need a quick interim solution? -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
