linux-kernel - [PATCH 1/3] fs/proc: extend the PAGEMAP

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Message-ID: <20250324065328.107678-2-avagin@google.com>
Date: Mon, 24 Mar 2025 06:53:26 +0000
From: Andrei Vagin <avagin@...gle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org, 
	David Hildenbrand <david@...hat.com>, Shuah Khan <shuah@...nel.org>, Jonathan Corbet <corbet@....net>, 
	criu@...ts.linux.dev, Andrei Vagin <avagin@...il.com>
Subject: [PATCH 1/3] fs/proc: extend the PAGEMAP_SCAN ioctl to report guard regions

From: Andrei Vagin <avagin@...il.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.

Acked-by: David Hildenbrand <david@...hat.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Signed-off-by: Andrei Vagin <avagin@...il.com>
---
 Documentation/admin-guide/mm/pagemap.rst |  1 +
 fs/proc/task_mmu.c                       | 17 ++++++++++-------
 include/uapi/linux/fs.h                  |  1 +
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
index a297e824f990..1f49762190eb 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 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 c17615e21a5d..cc35d8990c54 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 {
@@ -2108,12 +2109,14 @@ 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 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
-- 
2.49.0.395.g12beb8f557-goog