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fs/proc: extend the PAGEMAP_SCAN ioctl to report guard regions

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Patch series "fs/proc: extend the PAGEMAP_SCAN ioctl to report guard
regions", v2.

Introduce the PAGE_IS_GUARD flag in the PAGEMAP_SCAN ioctl to expose
information about guard regions.  This allows userspace tools, such as
CRIU, to detect and handle guard regions.

Currently, CRIU utilizes PAGEMAP_SCAN as a more efficient alternative to
parsing /proc/pid/pagemap.  Without this change, guard regions are
incorrectly reported as swap-anon regions, leading CRIU to attempt dumping
them and subsequently failing.

The series includes updates to the documentation and selftests to reflect
the new functionality.


This patch (of 3):

Introduce the PAGE_IS_GUARD flag in the PAGEMAP_SCAN ioctl to expose
information about guard regions.  This allows userspace tools, such as
CRIU, to detect and handle guard regions.

Link: https://lkml.kernel.org/r/20250324065328.107678-1-avagin@google.com
Link: https://lkml.kernel.org/r/20250324065328.107678-2-avagin@google.com
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Andrei Vagin 2025-03-24 06:53:26 +00:00 • committed by Andrew Morton
parent 7eeafde0ac
commit a516403787
3 changed files with 12 additions and 7 deletions
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1
Documentation/admin-guide/mm/pagemap.rst
View file

@ -250,6 +250,7 @@ Following flags about pages are currently supported:
- ``PAGE_IS_PFNZERO`` - Page has zero PFN
- ``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
The ``struct pm_scan_arg`` is used as the argument of the IOCTL.

17
fs/proc/task_mmu.c
View file

@ -2087,7 +2087,8 @@ static int pagemap_release(struct inode *inode, struct file *file)
#define PM_SCAN_CATEGORIES (PAGE_IS_WPALLOWED | PAGE_IS_WRITTEN | \
PAGE_IS_FILE | PAGE_IS_PRESENT | \
PAGE_IS_SWAPPED | PAGE_IS_PFNZERO | \
PAGE_IS_HUGE | PAGE_IS_SOFT_DIRTY)
PAGE_IS_HUGE | PAGE_IS_SOFT_DIRTY | \
PAGE_IS_GUARD)
#define PM_SCAN_FLAGS (PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC)
struct pagemap_scan_private {
@ -2128,12 +2129,14 @@ static unsigned long pagemap_page_category(struct pagemap_scan_private *p,
if (!pte_swp_uffd_wp_any(pte))
categories |= PAGE_IS_WRITTEN;
if (p->masks_of_interest & PAGE_IS_FILE) {
swp = pte_to_swp_entry(pte);
if (is_pfn_swap_entry(swp) &&
!folio_test_anon(pfn_swap_entry_folio(swp)))
categories |= PAGE_IS_FILE;
}
swp = pte_to_swp_entry(pte);
if (is_guard_swp_entry(swp))
categories |= PAGE_IS_GUARD;
else if ((p->masks_of_interest & PAGE_IS_FILE) &&
is_pfn_swap_entry(swp) &&
!folio_test_anon(pfn_swap_entry_folio(swp)))
categories |= PAGE_IS_FILE;
if (pte_swp_soft_dirty(pte))
categories |= PAGE_IS_SOFT_DIRTY;
}

1
include/uapi/linux/fs.h
View file

@ -361,6 +361,7 @@ typedef int __bitwise __kernel_rwf_t;
#define PAGE_IS_PFNZERO (1 << 5)
#define PAGE_IS_HUGE (1 << 6)
#define PAGE_IS_SOFT_DIRTY (1 << 7)
#define PAGE_IS_GUARD (1 << 8)
/*
* struct page_region - Page region with flags