On Thu, Jul 15, 2021 at 1:21 PM Kenneth Graunke <kenneth@xxxxxxxxxxxxx> wrote: > > On Thursday, July 15, 2021 4:27:44 AM PDT Tvrtko Ursulin wrote: > > > > On 15/07/2021 12:07, Daniel Vetter wrote: > > > On Thu, Jul 15, 2021 at 11:33:10AM +0100, Tvrtko Ursulin wrote: > > >> > > >> On 15/07/2021 11:15, Matthew Auld wrote: > > >>> From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > >>> > > >>> Jason Ekstrand requested a more efficient method than userptr+set-domain > > >>> to determine if the userptr object was backed by a complete set of pages > > >>> upon creation. To be more efficient than simply populating the userptr > > >>> using get_user_pages() (as done by the call to set-domain or execbuf), > > >>> we can walk the tree of vm_area_struct and check for gaps or vma not > > >>> backed by struct page (VM_PFNMAP). The question is how to handle > > >>> VM_MIXEDMAP which may be either struct page or pfn backed... > > >>> > > >>> With discrete are going to drop support for set_domain(), so offering a > > >>> way to probe the pages, without having to resort to dummy batches has > > >>> been requested. > > >>> > > >>> v2: > > >>> - add new query param for the PROPBE flag, so userspace can easily > > >>> check if the kernel supports it(Jason). > > >>> - use mmap_read_{lock, unlock}. > > >>> - add some kernel-doc. > > >> > > >> 1) > > >> > > >> I think probing is too weak to be offered as part of the uapi. What probes > > >> successfully at create time might not be there anymore at usage time. So if > > >> the pointer is not trusted at one point, why should it be at a later stage? > > >> > > >> Only thing which works for me is populate (so get_pages) at create time. But > > >> again with no guarantees they are still there at use time clearly > > >> documented. > > > > > > Populate is exactly as racy as probe. We don't support pinned userptr > > > anymore. > > > > Yes, wrote so myself - "..again with no guarantees they are still there > > at use time..". > > > > Perhaps I don't understand what problem is probe supposed to solve. It > > doesn't deal 1:1 with set_domain removal since that one actually did > > get_pages so that would be populate. But fact remains regardless that if > > userspace is given a pointer it doesn't trust, _and_ wants the check it > > for this reason or that, then probe solves nothing. Unless there is > > actually at minimum some protocol to reply to whoever sent the pointer > > like "not that pointer please". > > That's exactly the point. GL_AMD_pinned_memory requires us the OpenGL > implementation to return an error for "not that pointer, please", at the > time when said pointer is supplied - not at first use. > > Sure, there can be reasons why it might seem fine up front, and not work > later. But an early check of "just no, you're doing it totally wrong" > at the right moment can be helpful for application developers. While it > shouldn't really happen, if it ever did, it would be a lot more obvious > to debug than "much later on, when something randomly flushed the GPU > commands we were building, something went wrong, and we don't know why." And before someone chimes in saying that Vulkan doesn't need this because we can just VK_ERROR_DEVICE_LOST later, that's not true. We'd like to be able to return VK_ERROR_INVALID_EXTERNAL_HANDLE in the easily checkable cases like if they try to pass in a mmapped file. --Jason _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx