Re: [PATCH] fixup: mm/rmap: extend rmap and migration support device-private entries

[Andrew Morton]

On Sat, 15 Nov 2025 11:28:35 +1100 Balbir Singh <balb...@nvidia.com> wrote:

> Follow the pattern used in remove_migration_pte() in
> remove_migration_pmd(). Process the migration entries and if the entry
> type is device private, override the pmde with a device private entry
> and set the soft dirty and uffd_wp bits with the pmd_swp_mksoft_dirty
> and pmd_swp_mkuffd_wp
> 
> ...
>
> This fixup should be squashed into the patch "mm/rmap: extend rmap and
> migration support" of mm/mm-unstable
> 

OK.  After fixing up
mm-replace-pmd_to_swp_entry-with-softleaf_from_pmd.patch, mm.git's
mm/huge_memory.c has the below.  Please double-check.


void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
{
        struct folio *folio = page_folio(new);
        struct vm_area_struct *vma = pvmw->vma;
        struct mm_struct *mm = vma->vm_mm;
        unsigned long address = pvmw->address;
        unsigned long haddr = address & HPAGE_PMD_MASK;
        pmd_t pmde;
        softleaf_t entry;

        if (!(pvmw->pmd && !pvmw->pte))
                return;

        entry = softleaf_from_pmd(*pvmw->pmd);
        folio_get(folio);
        pmde = folio_mk_pmd(folio, READ_ONCE(vma->vm_page_prot));

        if (pmd_swp_soft_dirty(*pvmw->pmd))
                pmde = pmd_mksoft_dirty(pmde);
        if (softleaf_is_migration_write(entry))
                pmde = pmd_mkwrite(pmde, vma);
        if (pmd_swp_uffd_wp(*pvmw->pmd))
                pmde = pmd_mkuffd_wp(pmde);
        if (!softleaf_is_migration_young(entry))
                pmde = pmd_mkold(pmde);
        /* NOTE: this may contain setting soft-dirty on some archs */
        if (folio_test_dirty(folio) && softleaf_is_migration_dirty(entry))
                pmde = pmd_mkdirty(pmde);

        if (folio_is_device_private(folio)) {
                swp_entry_t entry;

                if (pmd_write(pmde))
                        entry = make_writable_device_private_entry(
                                                        page_to_pfn(new));
                else
                        entry = make_readable_device_private_entry(
                                                        page_to_pfn(new));
                pmde = swp_entry_to_pmd(entry);

                if (pmd_swp_soft_dirty(*pvmw->pmd))
                        pmde = pmd_swp_mksoft_dirty(pmde);
                if (pmd_swp_uffd_wp(*pvmw->pmd))
                        pmde = pmd_swp_mkuffd_wp(pmde);
        }

        if (folio_test_anon(folio)) {
                rmap_t rmap_flags = RMAP_NONE;

                if (!softleaf_is_migration_read(entry))
                        rmap_flags |= RMAP_EXCLUSIVE;

                folio_add_anon_rmap_pmd(folio, new, vma, haddr, rmap_flags);
        } else {
                folio_add_file_rmap_pmd(folio, new, vma);
        }
        VM_BUG_ON(pmd_write(pmde) && folio_test_anon(folio) && 
!PageAnonExclusive(new));
        set_pmd_at(mm, haddr, pvmw->pmd, pmde);

        /* No need to invalidate - it was non-present before */
        update_mmu_cache_pmd(vma, address, pvmw->pmd);
        trace_remove_migration_pmd(address, pmd_val(pmde));
}