On Fri, Nov 6, 2020 at 5:08 AM John Hubbard <jhubbard@xxxxxxxxxx> wrote: > > On 11/5/20 4:49 AM, Jason Gunthorpe wrote: > > On Thu, Nov 05, 2020 at 10:25:24AM +0100, Daniel Vetter wrote: > >>> /* > >>> * If we can't determine whether or not a pte is special, then fail immediately > >>> * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not > >>> * to be special. > >>> * > >>> * For a futex to be placed on a THP tail page, get_futex_key requires a > >>> * get_user_pages_fast_only implementation that can pin pages. Thus it's still > >>> * useful to have gup_huge_pmd even if we can't operate on ptes. > >>> */ > >> > >> We support hugepage faults in gpu drivers since recently, and I'm not > >> seeing a pud_mkhugespecial anywhere. So not sure this works, but probably > >> just me missing something again. > > > > It means ioremap can't create an IO page PUD, it has to be broken up. > > > > Does ioremap even create anything larger than PTEs? gpu drivers also tend to use vmf_insert_pfn* directly, so we can do on-demand paging and move buffers around. From what I glanced for lowest level we to the pte_mkspecial correctly (I think I convinced myself that vm_insert_pfn does that), but for pud/pmd levels it seems just yolo. remap_pfn_range seems to indeed split down to pte level always. > From my reading, yes. See ioremap_try_huge_pmd(). The ioremap here shouldn't matter, since this is for kernel-internal mappings. So that's all fine I think. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
