[PATCH 1/2] fs/proc: extend the PAGEMAP_SCAN ioctl to report guard regions

[Andrei Vagin <avagin@google.com>]

From: Andrei Vagin <avagin@gmail.com>

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.

Signed-off-by: Andrei Vagin <avagin@gmail.com>
---
 Documentation/admin-guide/mm/pagemap.rst | 1 +
 fs/proc/task_mmu.c                       | 8 ++++++--
 include/uapi/linux/fs.h                  | 1 +
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
index a297e824f990..7997b67ffc97 100644
--- a/Documentation/admin-guide/mm/pagemap.rst
+++ b/Documentation/admin-guide/mm/pagemap.rst
@@ -234,6 +234,7 @@ 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 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 c17615e21a5d..698d660bfee4 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -2067,7 +2067,8 @@ 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 {
@@ -2108,8 +2109,11 @@ static unsigned long pagemap_page_category(struct pagemap_scan_private *p,
 		if (!pte_swp_uffd_wp_any(pte))
 			categories |= PAGE_IS_WRITTEN;
 
+		swp = pte_to_swp_entry(pte);
+		if (is_guard_swp_entry(swp))
+			categories |= PAGE_IS_GUARD;
+
 		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;
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 2bbe00cf1248..8aa66c5f69b7 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -363,6 +363,7 @@ 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
-- 
2.49.0.rc1.451.g8f38331e32-goog