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imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=P+g7HWxD; spf=pass (imf27.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1770632654; a=rsa-sha256; cv=none; b=jWJ7ELnWvY3jEDKJK21BbjAD/RYK5i1ru8bssTYIWOZSxLA6ZlQDtS61rlWaCdeh2mVcjo 1A66LqBzftVY9ad9H5Y/JcELchqwHoCedpdg63SxI2AlBrd8D5YgRZmL2k1gekPzvGyHVp 1q1HJGy053RT4mtcQ+OSxxXIRMxaA6c= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 2298F60008; Mon, 9 Feb 2026 10:24:14 +0000 (UTC) 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 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 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: BF63940003 X-Stat-Signature: ppub8w5d3dknm18ty4ce1yuywcmuaeff X-Rspam-User: X-HE-Tag: 1770632654-773448 X-HE-Meta: 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 OpoWiW04 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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 2/9/26 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