On Fri, Nov 6, 2020 at 11:01 AM Daniel Vetter <daniel@xxxxxxxx> wrote: > > 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. So I dug around a bit more and ttm sets PFN_DEV | PFN_MAP to get past the various pft_t_devmap checks (see e.g. vmf_insert_pfn_pmd_prot()). x86-64 has ARCH_HAS_PTE_DEVMAP, and gup.c seems to handle these specially, but frankly I got totally lost in what this does. The comment above the pfn_t_devmap check makes me wonder whether doing this is correct or not. Also adding Thomas Hellstrom, who implemented the huge map support in ttm. -Daniel > 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 -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
