+ mm-thp-deny-thp-for-files-on-anonymous-inodes.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: thp: deny THP for files on anonymous inodes
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-thp-deny-thp-for-files-on-anonymous-inodes.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-thp-deny-thp-for-files-on-anonymous-inodes.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Deepanshu Kartikey <kartikey406@gmail.com>
Subject: mm: thp: deny THP for files on anonymous inodes
Date: Sat, 14 Feb 2026 05:45:35 +0530

file_thp_enabled() incorrectly allows THP for files on anonymous inodes
(e.g. guest_memfd and secretmem). These files are created via
alloc_file_pseudo(), which does not call get_write_access() and leaves
inode->i_writecount at 0. Combined with S_ISREG(inode->i_mode) being
true, they appear as read-only regular files when
CONFIG_READ_ONLY_THP_FOR_FS is enabled, making them eligible for THP
collapse.

Anonymous inodes can never pass the inode_is_open_for_write() check
since their i_writecount is never incremented through the normal VFS
open path. The right thing to do is to exclude them from THP eligibility
altogether, since CONFIG_READ_ONLY_THP_FOR_FS was designed for real
filesystem files (e.g. shared libraries), not for pseudo-filesystem
inodes.

For guest_memfd, this allows khugepaged and MADV_COLLAPSE to create
large folios in the page cache via the collapse path, but the
guest_memfd fault handler does not support large folios. This triggers
WARN_ON_ONCE(folio_test_large(folio)) in kvm_gmem_fault_user_mapping().

For secretmem, collapse_file() tries to copy page contents through the
direct map, but secretmem pages are removed from the direct map. This
can result in a kernel crash:

    BUG: unable to handle page fault for address: ffff88810284d000
    RIP: 0010:memcpy_orig+0x16/0x130
    Call Trace:
     collapse_file
     hpage_collapse_scan_file
     madvise_collapse

Secretmem is not affected by the crash on upstream as the memory failure
recovery handles the failed copy gracefully, but it still triggers
confusing false memory failure reports:

    Memory failure: 0x106d96f: recovery action for clean unevictable
    LRU page: Recovered

Check IS_ANON_FILE(inode) in file_thp_enabled() to deny THP for all
anonymous inode files.

Link: https://syzkaller.appspot.com/bug?extid=33a04338019ac7e43a44
Link: https://lore.kernel.org/linux-mm/CAEvNRgHegcz3ro35ixkDw39ES8=U6rs6S7iP0gkR9enr7HoGtA@mail.gmail.com
Link: https://lkml.kernel.org/r/20260214001535.435626-1-kartikey406@gmail.com
Fixes: 7fbb5e188248 ("mm: remove VM_EXEC requirement for THP eligibility")
Signed-off-by: Deepanshu Kartikey <Kartikey406@gmail.com>
Reported-by: syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=33a04338019ac7e43a44
Tested-by: syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com
Tested-by: Lance Yang <lance.yang@linux.dev>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Tested-by: Ackerley Tng <ackerleytng@google.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Fangrui Song <i@maskray.me>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/mm/huge_memory.c~mm-thp-deny-thp-for-files-on-anonymous-inodes
+++ a/mm/huge_memory.c
@@ -94,6 +94,9 @@ static inline bool file_thp_enabled(stru
 
 	inode = file_inode(vma->vm_file);
 
+	if (IS_ANON_FILE(inode))
+		return false;
+
 	return !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode);
 }
 
_

Patches currently in -mm which might be from kartikey406@gmail.com are

mm-thp-deny-thp-for-files-on-anonymous-inodes.patch