Commit a5164037 authored by Andrei Vagin's avatar Andrei Vagin Committed by Andrew Morton
Browse files

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

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: default avatarAndrei Vagin <avagin@gmail.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 7eeafde0

Documentation/admin-guide/mm/pagemap.rst

+1 −0
Original line number Diff line number Diff line
@@ -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.

fs/proc/task_mmu.c

+10 −7
Original line number Diff line number Diff line
@@ -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) &&

		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;

	}

include/uapi/linux/fs.h

+1 −0
Original line number Diff line number Diff line
@@ -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