From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4E7A934D4DC for ; Mon, 9 Feb 2026 10:24:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770632654; cv=none; b=q9jLe7mdYQVKdC6F+V5Njd34JR0HsCTK5LM1YEinzPEUTBiWO1sE2oBWyAgZdWHGkr6+K7lL8PiG0quoMqc3F3Rc/D5caUPQSapYeW3A5PIax0P8yQPNCC+eegQvoNXMvFEe6qL1DU4kAICgQPp7yHHx/aeS1DA+erz4/2/opJE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770632654; c=relaxed/simple; bh=7byzve2KBPNejNVzw6d0LoR5buYIQZxd6d4ggi5K93A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=VMEpuJwmFoHLhfi+zT9yBrGUo8wZqqbJ0sS5nfRpBOYRtx6UnIeTXuA4/hSB7VBXb3HMOtzPPCFAtkNabyS7QWiPIdSVcDi9tF6v1/+XOKZg247MCdg00FdU5Q8DQWfn1FN6VyXbFxME6HSN8UrXPt7tyh65AGJoGmWLwMi8mzw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=P+g7HWxD; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="P+g7HWxD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 86E48C116C6; Mon, 9 Feb 2026 10:24:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770632653; bh=7byzve2KBPNejNVzw6d0LoR5buYIQZxd6d4ggi5K93A=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=P+g7HWxDLSrBmFXhK2pT4GUqEBwZQxUiz5UcND2+oXAr8lBgnBxRYWVr0fYzUHtAS fY9DwTYePgsWD1AI52ZXywDOgq/25at8l5oMYXFUjnkiFD1EQ+eT6bqQUmAZdGu1dz gWOJ7rkQyA/RJKZCbCUxImYsNfs8U/tDf7jCdHb8qcCnALaOOKIB5zLXK/O4omGU0z IB7LJWWwUaL+S7K/MNDXmjZJI8g6ga9WyvxYcVeZmYnjRnrv57kTgaZqUj93WwKL6F w8Mr+jmFy6riGcZnKEk6up5imkQnaiL+aQPh4Vr/qOw71TC6mAkOkROyTYQWA/31Ee VeHutgLTteC+Q== Message-ID: <0d9cada8-7148-4a5c-a09d-120ef54559d7@kernel.org> Date: Mon, 9 Feb 2026 11:24:05 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: thp: Deny THP for guest_memfd and secretmem in file_thp_enabled() To: Deepanshu Kartikey , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, ackerleytng@google.com, seanjc@google.com, pbonzini@redhat.com, michael.roth@amd.com, vannapurve@google.com Cc: ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com References: <20260209033558.22943-1-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 On 2/9/26 04:35, Deepanshu Kartikey wrote: > file_thp_enabled() incorrectly returns true for guest_memfd and secretmem > inodes because they appear as regular read-only files when > CONFIG_READ_ONLY_THP_FOR_FS is enabled. This allows khugepaged and > MADV_COLLAPSE to create large folios in the page cache, but their fault > handlers do not support large folios. > > Add explicit checks for GUEST_MEMFD_MAGIC and SECRETMEM_MAGIC to reject > these filesystems early in file_thp_enabled(). > > Reported-by: syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=33a04338019ac7e43a44 > Tested-by: syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com > Signed-off-by: Deepanshu Kartikey So we were able to reproduce this with secretmem, right? We want to add "Fixes:" for the introducing commits, which would be he commits that enable secretmem and mapping of guest_memfd pages to user space. Can you identify them? And also Cc: stable@vger.kernel.org > --- > mm/huge_memory.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 40cf59301c21..4f57c78b57dd 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -93,6 +93,9 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma) > return false; > > inode = file_inode(vma->vm_file); > + if (inode->i_sb->s_magic == GUEST_MEMFD_MAGIC || > + inode->i_sb->s_magic == SECRETMEM_MAGIC) > + return false; That's nasty. We want some way to identify that through the mapping. Unfortunately CONFIG_READ_ONLY_THP_FOR_FS ignores any mapping_set_large_folios() configs by design. And CONFIG_READ_ONLY_THP_FOR_FS might go away soon, but we need a fix until then. While we can identify secretmem through vma_is_secretmem(), we can't do the same for guest_memfd as it's built as a module. Unfortunately AS_NO_DIRECT_MAP[1] won't work. Maybe introduce a AS_NO_READ_ONLY_THP_FOR_FS, which we can just easily rip out along with CONFIG_READ_ONLY_THP_FOR_FS later? [1] https://lore.kernel.org/r/20260126164445.11867-6-kalyazin@amazon.com -- Cheers, David