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b=b+ZIlK0okrsv6RLyo4uvDRQGNrt7EmSId8eFDX8Z1Lv24sFO4IGLmruZ1CiS58EV8 8Kdf66G5Q2/rY9D0mqG3aF4UjRZV7JpSl4A0jcOjJsZMHmZwCHPsN3Cyn5YCQRgSkx V6dlNG65Gd8fj/vcCwEBrdcGsyqDnZ4070E75eqYQNEtEYwm915JF1SBu+YeDjeJED +1FIFwMt0An2h/raGgzU4dQfB0tCaoO7cOtVNN6rsiG6azplH14Emt5aPTLPgoVMrD w7luaPgliHgkXViwpIc44DFJuxecnTbdgf5G6rJdp7RePQEXrMrQ95P3ftGh2Md6uE 2bt9eob2dYZJQ== Message-ID: <3ca2c5a7-66d4-42df-9f88-c2b6eaa0ecb1@kernel.org> Date: Sun, 15 Feb 2026 13:41:08 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: thp: deny THP for files on anonymous inodes To: Deepanshu Kartikey , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, i@maskray.me, shy828301@gmail.com, ackerleytng@google.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com, stable@vger.kernel.org References: <20260214001535.435626-1-kartikey406@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: D3CB81C0007 X-Stat-Signature: hm8cp6dpwnqptkksyh34xeysbiartqrt X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1771159278-204118 X-HE-Meta: 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 5BwhjFpX 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/14/26 01:15, Deepanshu Kartikey wrote: > 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 > Reported-by: syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=33a04338019ac7e43a44 > Fixes: 7fbb5e188248 ("mm: remove VM_EXEC requirement for THP eligibility") > Tested-by: syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com > Cc: stable@vger.kernel.org > Signed-off-by: Deepanshu Kartikey Acked-by: David Hildenbrand (Arm) -- Cheers, David