linux-kernel - [PATCH] /proc/pid/smaps: add mo info for vma in NOMMU system

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Message-ID: <20250607165335.87054-1-wangfushuai@baidu.com>
Date: Sun, 8 Jun 2025 00:53:35 +0800
From: wangfushuai <wangfushuai@...du.com>
To: <akpm@...ux-foundation.org>, <david@...hat.com>, <andrii@...nel.org>,
	<osalvador@...e.de>, <Liam.Howlett@...cle.com>, <christophe.leroy@...roup.eu>
CC: <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	wangfushuai <wangfushuai@...du.com>
Subject: [PATCH] /proc/pid/smaps: add mo info for vma in NOMMU system

Add mo in /proc/[pid]/smaps to indicate vma is marked VM_MAYOVERLAY,
which means the file mapping may overlay in NOMMU system.

Fixes: b6b7a8faf05c ("mm/nommu: don't use VM_MAYSHARE for MAP_PRIVATE mappings")
Signed-off-by: wangfushuai <wangfushuai@...du.com>
---
 Documentation/filesystems/proc.rst | 1 +
 fs/proc/task_mmu.c                 | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 2a17865dfe39..d280594656a3 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -609,6 +609,7 @@ encoded manner. The codes are the following:
     uw    userfaultfd wr-protect tracking
     ss    shadow/guarded control stack page
     sl    sealed
+    mo    may overlay file mapping
     ==    =======================================
 
 Note that there is no guarantee that every flag and associated mnemonic will
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 27972c0749e7..ad08807847de 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -970,7 +970,11 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 		[ilog2(VM_HUGEPAGE)]	= "hg",
 		[ilog2(VM_NOHUGEPAGE)]	= "nh",
 		[ilog2(VM_MERGEABLE)]	= "mg",
+#ifdef CONFIG_MMU
 		[ilog2(VM_UFFD_MISSING)]= "um",
+#else
+		[ilog2(VM_MAYOVERLAY)]	= "mo",
+#endif
 		[ilog2(VM_UFFD_WP)]	= "uw",
 #ifdef CONFIG_ARM64_MTE
 		[ilog2(VM_MTE)]		= "mt",
-- 
2.36.1