Commit 2c7ad9a5 authored by Ryan Roberts's avatar Ryan Roberts Committed by Andrew Morton
Browse files

fs/proc/task_mmu: fix uffd-wp confusion in pagemap_scan_pmd_entry() 

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: 12f6b01a ("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: default avatarRyan Roberts <ryan.roberts@arm.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarMuhammad Usama Anjum <usama.anjum@collabora.com>
Tested-by: default avatarMuhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent c70dce49

fs/proc/task_mmu.c

+13 −9
Original line number Diff line number Diff line
@@ -1817,10 +1817,8 @@ static unsigned long pagemap_page_category(struct pagemap_scan_private *p, 
}



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 *pmd, unsigned long start, 
	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 *pmd, unsigned long start, 
	    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 *pmd, unsigned long start, 
				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 *pmd, unsigned long start, 
	}



	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 *pmd, unsigned long start, 
		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;