On Tue, Jan 27, 2026 at 02:16:36PM +0100, Thomas Zimmermann wrote:
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -553,17 +553,18 @@ EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create);
> static bool drm_gem_shmem_try_map_pmd(struct vm_fault *vmf, unsigned long
> addr,
> struct page *page)
> {
> -#ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP
> - unsigned long pfn = page_to_pfn(page);
> - unsigned long paddr = pfn << PAGE_SHIFT;
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> + phys_addr_t paddr = page_to_phys(page);
> bool aligned = (addr & ~PMD_MASK) == (paddr & ~PMD_MASK);
>
> - if (aligned &&
> - pmd_none(*vmf->pmd) &&
> - folio_test_pmd_mappable(page_folio(page))) {
> - pfn &= PMD_MASK >> PAGE_SHIFT;
> - if (vmf_insert_pfn_pmd(vmf, pfn, false) == VM_FAULT_NOPAGE)
> - return true;
> + if (aligned && pmd_none(*vmf->pmd)) {
> + struct folio *folio = page_folio(page);
> +
> + if (folio_test_pmd_mappable(folio)) {
> + /* Read-only mapping; split upon write fault */
> + if (vmf_insert_folio_pmd(vmf, folio, false) ==
> VM_FAULT_NOPAGE)
> + return true;
> + }
> }
It would feel more natural to me to have this function return vm_fault_t
instead of a bool. What do you think?
> + pgoff_t page_offset = vmf->pgoff - vma->vm_pgoff; /* page offset within
> VMA */
> + struct page *page = pages[page_offset];
> + vm_fault_t ret;
[...]
> - if (drm_gem_shmem_try_map_pmd(vmf, vmf->address, pages[page_offset])) {
> - ret = VM_FAULT_NOPAGE;
> - goto out;
> + page = pages[page_offset];
Can page_offset have changed at this point?
> + if (drm_gem_shmem_try_map_pmd(vmf, vmf->address, page)) {
> + ret = VM_FAULT_NOPAGE;
> + } else {
> + struct folio *folio = page_folio(page);
> +
> + get_page(page);
folio_get(folio);
> - vm_flags_set(vma, VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
> + vm_flags_mod(vma, VM_DONTEXPAND | VM_DONTDUMP, VM_PFNMAP);
Just so you know, this is going to change observable behaviour, maybe
in a good way. For example, we'll now be able to do O_DIRECT I/O to
this range and ptrace accesses. I think everything will be fine, but
VM_PFNMAP does prohibit some things which are now allowed.
