From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oo1-f69.google.com (mail-oo1-f69.google.com [209.85.161.69]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 14C6A2EE607 for ; Mon, 9 Feb 2026 13:11:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.161.69 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770642714; cv=none; b=dXlziDBtxBgfOs4W+p4MSLaz70w2ldjFQmcArfXCc4M2uKmwCMGc0YmPAVY9nxkkJn9uL8cMHBziKb0ugOuQH+N8vc7UIMzEw3yyOZao+A3HSCdAeCUg8MN9CT7yFPC0U4Jr9VZPAAICOK84adPApMSxthfvA6cFzPzvQ3/hxgg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770642714; c=relaxed/simple; bh=Qt0ID1PYQn7rcLoK7BQlpdU+nsvwA2eGoMpSQj+94NA=; h=MIME-Version:Date:In-Reply-To:Message-ID:Subject:From:To: Content-Type; b=g40b3QKjmBzRD9EBjn5cxy9bDuyqLgvnptXxgaoct2JpoZ4PdR6H5JXEdgumYZozxqUZLJrw7gVIygdsytpEZIWpX9HA8vtwxzIizfMRINUQSHwJbIejZJm0bvAMLszhbw6PqIpEiO8ktdEyTMwFjUkOZ5RRGmZmbnTsMuirj2c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com; arc=none smtp.client-ip=209.85.161.69 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com Received: by mail-oo1-f69.google.com with SMTP id 006d021491bc7-66b70fffe1dso17839073eaf.2 for ; Mon, 09 Feb 2026 05:11:53 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1770642713; x=1771247513; h=to:from:subject:message-id:in-reply-to:date:mime-version :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=sW1sL2oj2hnvfBJDp7ywg8QUpK43kSYJW2+NHgljJKs=; b=dQoSxirNoZj9Bs1dsP67flRZtWGfAi7DJF4ZCKtkTgRMtwGw6FEJ2qNWumemerp6+g KTfNPlPBKMBB5BhVbK2YHiUivK0hqdOyOD6eK6QRrTXSIxuQFK8bodH0qZG9B0GF1IVz J6UoVIB5Ty7q9y4aq8qk70XxHdCov+lYKyD8dyzOva1jOuLJA0M8nN3B9SlPUIW2sunm bSK/uB3fl4RlScrx6c7XqVR4ZpeU7r5fTr6CHMDeZ64sIKsxoWaOk9mbja6I2XwZuMiW K+0zEjKSLca7Cn7llhqPBbNY9zzYs9w/oFkKdVLQ8SgQ4G0kulbC+JUBh0N4yxdJbuMP i81Q== X-Gm-Message-State: AOJu0YxsSZQ8wxuJzLOjQHRKr9kGlnK8PpRv+AbFxPZaVkmBwWeuNmuD 3Vdwu/gYViMut1fJf2CSPFtaF/HiRaJOFk9JPdoWCua1rdQ7hU5iBYuZugI/+P210XKutmzi11j LNoZ4WYTODX6ys888WqV4aYCC3xQq65nFC46H91LCFUEhF8IwgXCCyEPCfxo= Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a05:6820:16c:b0:66d:e4b4:a1ad with SMTP id 006d021491bc7-66de4c3e76dmr2850270eaf.40.1770642713016; Mon, 09 Feb 2026 05:11:53 -0800 (PST) Date: Mon, 09 Feb 2026 05:11:52 -0800 In-Reply-To: <697d115a.050a0220.1d61ec.0004.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6989dd18.a00a0220.34fa92.0045.GAE@google.com> Subject: Forwarded: [PATCH] mm: thp: Deny THP for guest_memfd and secretmem in file_thp_enabled() From: syzbot To: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" For archival purposes, forwarding an incoming command email to linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com. *** Subject: [PATCH] mm: thp: Deny THP for guest_memfd and secretmem in file_thp_enabled() Author: kartikey406@gmail.com #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master file_thp_enabled() incorrectly returns true for guest_memfd and secretmem inodes because they use alloc_file_pseudo() which does not call get_write_access(), leaving i_writecount at 0. Combined with S_ISREG being true, these pseudo-filesystem inodes appear as read-only regular files when CONFIG_READ_ONLY_THP_FOR_FS is enabled. This allows khugepaged and MADV_COLLAPSE to create large folios in the page cache via the TVA_COLLAPSE path, but their fault handlers do not support large folios. For guest_memfd this triggers WARN_ON_ONCE(folio_test_large(folio)) in kvm_gmem_fault_user_mapping(). Introduce AS_NO_READ_ONLY_THP_FOR_FS address_space flag to allow filesystems to opt out of CONFIG_READ_ONLY_THP_FOR_FS. Set this flag in both guest_memfd and secretmem inode setup. This flag can be easily removed along with CONFIG_READ_ONLY_THP_FOR_FS when it goes away. Reported-by: syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=33a04338019ac7e43a44 Signed-off-by: Deepanshu Kartikey --- include/linux/pagemap.h | 1 + mm/huge_memory.c | 3 +++ mm/secretmem.c | 3 ++- virt/kvm/guest_memfd.c | 1 + 4 files changed, 7 insertions(+), 1 deletion(-) diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index ec442af3f886..23f559fc1a4c 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -211,6 +211,7 @@ enum mapping_flags { AS_KERNEL_FILE = 10, /* mapping for a fake kernel file that shouldn't account usage to user cgroups */ AS_NO_DATA_INTEGRITY = 11, /* no data integrity guarantees */ + AS_NO_READ_ONLY_THP_FOR_FS = 12, /* Bits 16-25 are used for FOLIO_ORDER */ AS_FOLIO_ORDER_BITS = 5, AS_FOLIO_ORDER_MIN = 16, diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 40cf59301c21..4bdda92ce01e 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -94,6 +94,9 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma) inode = file_inode(vma->vm_file); + if (test_bit(AS_NO_READ_ONLY_THP_FOR_FS, &inode->i_mapping->flags)) + return false; + return !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode); } diff --git a/mm/secretmem.c b/mm/secretmem.c index edf111e0a1bb..56d93a74f5fc 100644 --- a/mm/secretmem.c +++ b/mm/secretmem.c @@ -205,7 +205,8 @@ static struct file *secretmem_file_create(unsigned long flags) mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); mapping_set_unevictable(inode->i_mapping); - + set_bit(AS_NO_READ_ONLY_THP_FOR_FS, &inode->i_mapping->flags); + inode->i_op = &secretmem_iops; inode->i_mapping->a_ops = &secretmem_aops; diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index fdaea3422c30..b93a324c81bd 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -597,6 +597,7 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) inode->i_size = size; mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); mapping_set_inaccessible(inode->i_mapping); + set_bit(AS_NO_READ_ONLY_THP_FOR_FS, &inode->i_mapping->flags); /* Unmovable mappings are supposed to be marked unevictable as well. */ WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping)); -- 2.43.0