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: 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>

diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
index afce291649dd61fb8014f749c18cb35ca74b6183..e60e9211fd9b2bf59bb14f298d2707f218ffd613 100644 (file)
--- a/Documentation/admin-guide/mm/pagemap.rst
+++ b/Documentation/admin-guide/mm/pagemap.rst
@@ -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.
 

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 994cde10e3f4d327b349e98a1a30519872f90f4e..b9e4fbbdf6e6790a7515193070b61c7adfc5c1a9 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -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;
        }

diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index e762e1af650c4bf08766ba7a8ab7a2288e987039..0098b0ce8ccb1f194f67972b31265c8e82f7bf58 100644 (file)
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -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