On Mon, 6 Jul 2026 09:48:00 +0100 Kiryl Shutsemau <[email protected]> wrote:
> From: "Kiryl Shutsemau (Meta)" <[email protected]> > > PAGEMAP_SCAN already reports PAGE_IS_WRITTEN from the inverted uffd > PTE bit, targeting the UFFDIO_WRITEPROTECT workflow. UFFDIO_RWPROTECT > reuses the same PTE bit as a marker for read-write protection, but > "has been written" and "has been accessed" are distinct semantic > signals — they happen to share one PTE bit today only because the two > implementations share infrastructure. > > Give RWP its own pagemap category so the UAPI does not conflate them: > > PAGE_IS_WRITTEN reported on VM_UFFD_WP VMAs, !pte_uffd(pte) > PAGE_IS_ACCESSED reported on VM_UFFD_RWP VMAs, !pte_uffd(pte) > > Both still read the same PTE bit today, but each is scoped to the VMA > whose registered mode makes the bit meaningful. If a future > implementation moves RWP to a separate PTE bit, only PAGE_IS_ACCESSED > switches over. > > This is a UAPI narrowing. Outside VM_UFFD_WP VMAs the uffd bit is > always clear, so PAGEMAP_SCAN used to flag PAGE_IS_WRITTEN on every > present PTE there — a meaningless duplicate of PAGE_IS_PRESENT. Now > PAGE_IS_WRITTEN fires only inside VM_UFFD_WP VMAs. > > pagemap_hugetlb_category() now takes the vma like its PTE/PMD peers. > > Signed-off-by: Kiryl Shutsemau <[email protected]> > Assisted-by: Claude:claude-opus-4-6 > Acked-by: Mike Rapoport (Microsoft) <[email protected]> > --- > Documentation/admin-guide/mm/pagemap.rst | 13 +++-- > fs/proc/task_mmu.c | 63 +++++++++++++++++------- > include/uapi/linux/fs.h | 1 + > tools/include/uapi/linux/fs.h | 1 + > 4 files changed, 57 insertions(+), 21 deletions(-) > > diff --git a/Documentation/admin-guide/mm/pagemap.rst > b/Documentation/admin-guide/mm/pagemap.rst > index c57e61b5d8aa..ffa690a171c8 100644 > --- a/Documentation/admin-guide/mm/pagemap.rst > +++ b/Documentation/admin-guide/mm/pagemap.rst > @@ -19,8 +19,11 @@ There are four components to pagemap: > * Bit 55 pte is soft-dirty (see > Documentation/admin-guide/mm/soft-dirty.rst) > * Bit 56 page exclusively mapped (since 4.2) > - * Bit 57 pte is uffd-wp write-protected (since 5.13) (see > - Documentation/admin-guide/mm/userfaultfd.rst) > + * Bit 57 pte is tracked by userfaultfd (since 5.13) — in a > + ``VM_UFFD_WP`` VMA this indicates a write-protected PTE; in a > + ``VM_UFFD_RWP`` VMA it indicates an RWP-protected PTE. WP and > + RWP are mutually exclusive per VMA, so the meaning is > + unambiguous. See Documentation/admin-guide/mm/userfaultfd.rst. > * Bit 58 pte is a guard region (since 6.15) (see madvise (2) man > page) > * Bits 59-60 zero > * Bit 61 page is file-page or shared-anon (since 3.5) > @@ -244,7 +247,8 @@ in this IOCTL: > Following flags about pages are currently supported: > > - ``PAGE_IS_WPALLOWED`` - Page has async-write-protection enabled > -- ``PAGE_IS_WRITTEN`` - Page has been written to from the time it was write > protected > +- ``PAGE_IS_WRITTEN`` - Page in a ``UFFDIO_REGISTER_MODE_WP`` VMA has been > + written to since it was write-protected. Only reported inside such VMAs. > - ``PAGE_IS_FILE`` - Page is file backed > - ``PAGE_IS_PRESENT`` - Page is present in the memory > - ``PAGE_IS_SWAPPED`` - Page is in swapped > @@ -252,6 +256,9 @@ Following flags about pages are currently supported: > - ``PAGE_IS_HUGE`` - Page is PMD-mapped THP or Hugetlb backed > - ``PAGE_IS_SOFT_DIRTY`` - Page is soft-dirty > - ``PAGE_IS_GUARD`` - Page is a part of a guard region > +- ``PAGE_IS_ACCESSED`` - Page in a ``UFFDIO_REGISTER_MODE_RWP`` VMA has been > + accessed since RWP was applied. Only reported inside such VMAs. See > + Documentation/admin-guide/mm/userfaultfd.rst for the RWP workflow. > > The ``struct pm_scan_arg`` is used as the argument of the IOCTL. > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 5b55c59573a3..2d724156763d 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -2283,7 +2283,7 @@ static const struct mm_walk_ops pagemap_ops = { > * Bits 5-54 swap offset if swapped > * Bit 55 pte is soft-dirty (see > Documentation/admin-guide/mm/soft-dirty.rst) > * Bit 56 page exclusively mapped > - * Bit 57 pte is uffd-wp write-protected > + * Bit 57 pte is tracked by userfaultfd (uffd-wp or RWP) > * Bit 58 pte is a guard region > * Bits 59-60 zero > * Bit 61 page is file-page or shared-anon > @@ -2418,7 +2418,7 @@ static int pagemap_release(struct inode *inode, struct > file *file) > PAGE_IS_FILE | PAGE_IS_PRESENT | \ > PAGE_IS_SWAPPED | PAGE_IS_PFNZERO | \ > PAGE_IS_HUGE | PAGE_IS_SOFT_DIRTY | \ > - PAGE_IS_GUARD) > + PAGE_IS_GUARD | PAGE_IS_ACCESSED) > #define PM_SCAN_FLAGS (PM_SCAN_WP_MATCHING | > PM_SCAN_CHECK_WPASYNC) > > struct pagemap_scan_private { > @@ -2443,8 +2443,12 @@ static unsigned long pagemap_page_category(struct > pagemap_scan_private *p, > > categories = PAGE_IS_PRESENT; > > - if (!pte_uffd(pte)) > - categories |= PAGE_IS_WRITTEN; > + if (!pte_uffd(pte)) { > + if (userfaultfd_wp(vma)) > + categories |= PAGE_IS_WRITTEN; > + if (userfaultfd_rwp(vma)) > + categories |= PAGE_IS_ACCESSED; > + } The above is an ABI change for existing PAGEMAP_SCAN users although not sure if there is someone that cares. Would below be a better alternative to limit the ABI change? if (!pte_uffd(pte)) { if (userfaultfd_rwp(vma)) categories |= PAGE_IS_ACCESSED; else categories |= PAGE_IS_WRITTEN; } > > if (p->masks_of_interest & PAGE_IS_FILE) { > page = vm_normal_page(vma, addr, pte); > @@ -2461,8 +2465,12 @@ static unsigned long pagemap_page_category(struct > pagemap_scan_private *p, > > categories = PAGE_IS_SWAPPED; > > - if (!pte_swp_uffd_any(pte)) > - categories |= PAGE_IS_WRITTEN; > + if (!pte_swp_uffd_any(pte)) { > + if (userfaultfd_wp(vma)) > + categories |= PAGE_IS_WRITTEN; > + if (userfaultfd_rwp(vma)) > + categories |= PAGE_IS_ACCESSED; > + } > > entry = softleaf_from_pte(pte); > if (softleaf_is_guard_marker(entry)) > @@ -2511,8 +2519,12 @@ static unsigned long pagemap_thp_category(struct > pagemap_scan_private *p, > struct page *page; > > categories |= PAGE_IS_PRESENT; > - if (!pmd_uffd(pmd)) > - categories |= PAGE_IS_WRITTEN; > + if (!pmd_uffd(pmd)) { > + if (userfaultfd_wp(vma)) > + categories |= PAGE_IS_WRITTEN; > + if (userfaultfd_rwp(vma)) > + categories |= PAGE_IS_ACCESSED; > + } > > if (p->masks_of_interest & PAGE_IS_FILE) { > page = vm_normal_page_pmd(vma, addr, pmd); > @@ -2526,8 +2538,12 @@ static unsigned long pagemap_thp_category(struct > pagemap_scan_private *p, > categories |= PAGE_IS_SOFT_DIRTY; > } else { > categories |= PAGE_IS_SWAPPED; > - if (!pmd_swp_uffd(pmd)) > - categories |= PAGE_IS_WRITTEN; > + if (!pmd_swp_uffd(pmd)) { > + if (userfaultfd_wp(vma)) > + categories |= PAGE_IS_WRITTEN; > + if (userfaultfd_rwp(vma)) > + categories |= PAGE_IS_ACCESSED; > + } > if (pmd_swp_soft_dirty(pmd)) > categories |= PAGE_IS_SOFT_DIRTY; > > @@ -2560,7 +2576,8 @@ static void make_uffd_wp_pmd(struct vm_area_struct *vma, > #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ > > #ifdef CONFIG_HUGETLB_PAGE > -static unsigned long pagemap_hugetlb_category(pte_t pte) > +static unsigned long pagemap_hugetlb_category(struct vm_area_struct *vma, > + pte_t pte) > { > unsigned long categories = PAGE_IS_HUGE; > > @@ -2575,8 +2592,12 @@ static unsigned long pagemap_hugetlb_category(pte_t > pte) > if (pte_present(pte)) { > categories |= PAGE_IS_PRESENT; > > - if (!huge_pte_uffd(pte)) > - categories |= PAGE_IS_WRITTEN; > + if (!huge_pte_uffd(pte)) { > + if (userfaultfd_wp(vma)) > + categories |= PAGE_IS_WRITTEN; > + if (userfaultfd_rwp(vma)) > + categories |= PAGE_IS_ACCESSED; > + } > if (!PageAnon(pte_page(pte))) > categories |= PAGE_IS_FILE; > if (is_zero_pfn(pte_pfn(pte))) > @@ -2586,8 +2607,12 @@ static unsigned long pagemap_hugetlb_category(pte_t > pte) > } else { > categories |= PAGE_IS_SWAPPED; > > - if (!pte_swp_uffd_any(pte)) > - categories |= PAGE_IS_WRITTEN; > + if (!pte_swp_uffd_any(pte)) { > + if (userfaultfd_wp(vma)) > + categories |= PAGE_IS_WRITTEN; > + if (userfaultfd_rwp(vma)) > + categories |= PAGE_IS_ACCESSED; > + } > if (pte_swp_soft_dirty(pte)) > categories |= PAGE_IS_SOFT_DIRTY; > } > @@ -2863,7 +2888,8 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned > long start, > goto flush_and_return; > } > > - if (!p->arg.category_anyof_mask && !p->arg.category_inverted && > + if (userfaultfd_wp(vma) && !p->arg.category_anyof_mask && > + !p->arg.category_inverted && > p->arg.category_mask == PAGE_IS_WRITTEN && > p->arg.return_mask == PAGE_IS_WRITTEN) { > for (addr = start; addr < end; pte++, addr += PAGE_SIZE) { > @@ -2938,7 +2964,8 @@ static int pagemap_scan_hugetlb_entry(pte_t *ptep, > unsigned long hmask, > /* Go the short route when not write-protecting pages. */ > > pte = huge_ptep_get(walk->mm, start, ptep); > - categories = p->cur_vma_category | > pagemap_hugetlb_category(pte); > + categories = p->cur_vma_category | > + pagemap_hugetlb_category(vma, pte); > > if (!pagemap_scan_is_interesting_page(categories, p)) > return 0; > @@ -2950,7 +2977,7 @@ static int pagemap_scan_hugetlb_entry(pte_t *ptep, > unsigned long hmask, > ptl = huge_pte_lock(hstate_vma(vma), vma->vm_mm, ptep); > > pte = huge_ptep_get(walk->mm, start, ptep); > - categories = p->cur_vma_category | pagemap_hugetlb_category(pte); > + categories = p->cur_vma_category | pagemap_hugetlb_category(vma, pte); > > if (!pagemap_scan_is_interesting_page(categories, p)) > goto out_unlock; > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h > index bd87262f2e34..34c6f219462a 100644 > --- a/include/uapi/linux/fs.h > +++ b/include/uapi/linux/fs.h > @@ -471,6 +471,7 @@ typedef int __bitwise __kernel_rwf_t; > #define PAGE_IS_HUGE (1 << 6) > #define PAGE_IS_SOFT_DIRTY (1 << 7) > #define PAGE_IS_GUARD (1 << 8) > +#define PAGE_IS_ACCESSED (1 << 9) > > /* > * struct page_region - Page region with flags > diff --git a/tools/include/uapi/linux/fs.h b/tools/include/uapi/linux/fs.h > index 24ddf7bc4f25..f0a26309b6d5 100644 > --- a/tools/include/uapi/linux/fs.h > +++ b/tools/include/uapi/linux/fs.h > @@ -364,6 +364,7 @@ typedef int __bitwise __kernel_rwf_t; > #define PAGE_IS_HUGE (1 << 6) > #define PAGE_IS_SOFT_DIRTY (1 << 7) > #define PAGE_IS_GUARD (1 << 8) > +#define PAGE_IS_ACCESSED (1 << 9) > > /* > * struct page_region - Page region with flags > -- > 2.54.0 > >
