[PATCH 6.8 318/336] fs/proc/task_mmu: fix uffd-wp confusion in pagemap_scan_pmd_entry()

Greg Kroah-Hartman
2024-05-14T10:56:43Z

From: Ryan Roberts <ryan.roberts@arm.com>

commit 2c7ad9a590d1a99ec59c7d90cef41e2b296944c4 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/proc/task_mmu.c | 22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)

--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1818,10 +1818,8 @@ 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;

@@ -2176,9 +2174,12 @@ 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;
@@ -2191,8 +2192,10 @@ 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);
@@ -2200,7 +2203,7 @@ 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;
@@ -2209,8 +2212,9 @@ 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))
@@ -2225,7 +2229,7 @@ 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;