The patch titled Subject: fs/proc/task_mmu: fix uffd-wp confusion in pagemap_scan_pmd_entry() has been added to the -mm mm-hotfixes-unstable branch. Its filename is fs-proc-task_mmu-fix-uffd-wp-confusion-in-pagemap_scan_pmd_entry.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Ryan Roberts ryan.roberts@arm.com Subject: fs/proc/task_mmu: fix uffd-wp confusion in pagemap_scan_pmd_entry() Date: Mon, 29 Apr 2024 12:41:04 +0100

pagemap_scan_pmd_entry() checks if uffd-wp is set on each pte to avoid unnecessary if set. However it was previously checking with `pte_uffd_wp(ptep_get(pte))` without first confirming that the pte was present. It is only valid to call pte_uffd_wp() for present ptes. For swap ptes, pte_swp_uffd_wp() must be called because the uffd-wp bit may be kept in a different position, depending on the arch.

This was leading to test failures in the pagemap_ioctl mm selftest, when bringing up uffd-wp support on arm64 due to incorrectly interpretting the uffd-wp status of migration entries.

Let's fix this by using the correct check based on pte_present(). While we are at it, let's pass the pte to make_uffd_wp_pte() to avoid the pointless extra ptep_get() which can't be optimized out due to READ_ONCE() on many arches.

Link: https://lkml.kernel.org/r/20240429114104.182890-1-ryan.roberts@arm.com Fixes: 12f6b01a0bcb ("fs/proc/task_mmu: add fast paths to get/clear PAGE_IS_WRITTEN flag") Closes: https://lore.kernel.org/linux-arm-kernel/ZiuyGXt0XWwRgFh9@x1n/ Signed-off-by: Ryan Roberts ryan.roberts@arm.com Acked-by: David Hildenbrand david@redhat.com Reviewed-by: Muhammad Usama Anjum usama.anjum@collabora.com Tested-by: Muhammad Usama Anjum usama.anjum@collabora.com Cc: Peter Xu peterx@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

fs/proc/task_mmu.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-)

--- a/fs/proc/task_mmu.c~fs-proc-task_mmu-fix-uffd-wp-confusion-in-pagemap_scan_pmd_entry +++ a/fs/proc/task_mmu.c @@ -1817,10 +1817,8 @@ static unsigned long pagemap_page_catego }

static void make_uffd_wp_pte(struct vm_area_struct *vma, - unsigned long addr, pte_t *pte) + unsigned long addr, pte_t *pte, pte_t ptent) { - pte_t ptent = ptep_get(pte); - if (pte_present(ptent)) { pte_t old_pte;

@@ -2175,9 +2173,12 @@ static int pagemap_scan_pmd_entry(pmd_t if ((p->arg.flags & PM_SCAN_WP_MATCHING) && !p->vec_out) { /* Fast path for performing exclusive WP */ for (addr = start; addr != end; pte++, addr += PAGE_SIZE) { - if (pte_uffd_wp(ptep_get(pte))) + pte_t ptent = ptep_get(pte); + + if ((pte_present(ptent) && pte_uffd_wp(ptent)) || + pte_swp_uffd_wp_any(ptent)) continue; - make_uffd_wp_pte(vma, addr, pte); + make_uffd_wp_pte(vma, addr, pte, ptent); if (!flush_end) start = addr; flush_end = addr + PAGE_SIZE; @@ -2190,8 +2191,10 @@ static int pagemap_scan_pmd_entry(pmd_t p->arg.return_mask == PAGE_IS_WRITTEN) { for (addr = start; addr < end; pte++, addr += PAGE_SIZE) { unsigned long next = addr + PAGE_SIZE; + pte_t ptent = ptep_get(pte);

- if (pte_uffd_wp(ptep_get(pte))) + if ((pte_present(ptent) && pte_uffd_wp(ptent)) || + pte_swp_uffd_wp_any(ptent)) continue; ret = pagemap_scan_output(p->cur_vma_category | PAGE_IS_WRITTEN, p, addr, &next); @@ -2199,7 +2202,7 @@ static int pagemap_scan_pmd_entry(pmd_t break; if (~p->arg.flags & PM_SCAN_WP_MATCHING) continue; - make_uffd_wp_pte(vma, addr, pte); + make_uffd_wp_pte(vma, addr, pte, ptent); if (!flush_end) start = addr; flush_end = next; @@ -2208,8 +2211,9 @@ static int pagemap_scan_pmd_entry(pmd_t }

for (addr = start; addr != end; pte++, addr += PAGE_SIZE) { + pte_t ptent = ptep_get(pte); unsigned long categories = p->cur_vma_category | - pagemap_page_category(p, vma, addr, ptep_get(pte)); + pagemap_page_category(p, vma, addr, ptent); unsigned long next = addr + PAGE_SIZE;

if (!pagemap_scan_is_interesting_page(categories, p)) @@ -2224,7 +2228,7 @@ static int pagemap_scan_pmd_entry(pmd_t if (~categories & PAGE_IS_WRITTEN) continue;

- make_uffd_wp_pte(vma, addr, pte); + make_uffd_wp_pte(vma, addr, pte, ptent); if (!flush_end) start = addr; flush_end = next; _

Patches currently in -mm which might be from ryan.roberts@arm.com are

fs-proc-task_mmu-fix-uffd-wp-confusion-in-pagemap_scan_pmd_entry.patch selftests-mm-soft-dirty-should-fail-if-a-testcase-fails.patch mm-fix-race-between-__split_huge_pmd_locked-and-gup-fast.patch