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 18C12368264 for ; Mon, 9 Feb 2026 10:42:00 +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=1770633721; cv=none; b=IHl027h00PBBM+LkEsZibMLvxlN4AxP/Vu7oLfBw8+Zb1EvYUn3t5t9P6tbgbXvH/ipa859YV2flh1uny/vGVO+ZBH7gRz3EhOLWvqpHLiw4WQpKRqsw8//OtxLMnopdhGB4jQicYVrB2mUUda+lkk0CIEUHuB5OAspxtQzxjWM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770633721; c=relaxed/simple; bh=ywJCRbCgffCqqfChHalI2gIpjQYUmGoILfzVpNH7JE0=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=IXgF4LplC18G2XAtt5Uyzr/1sviSO+YrN4x1l77wvAqdnSqsYOff8LQKMCEOOU7l+AWF3fVh1jj8ayoqVk9H/4KRTgCABPYGnNfY2acXDmC9c0gVY5DV6ee6i2ZUy9+CoTQMZVsEM3UZ5vOEN5x+7FSdAFvbMUYgseLzzp7bWVo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=S5DYD3/r; 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="S5DYD3/r" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0FDA5C116C6; Mon, 9 Feb 2026 10:41:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770633720; bh=ywJCRbCgffCqqfChHalI2gIpjQYUmGoILfzVpNH7JE0=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=S5DYD3/rPRNhXUdylNPOOMeREFxP8EedkjL2Dg/gOs00I8eQtLP0qPh/M4UxzV9ab CArMqgdfjrcXuo+UI5gA7uiE0brOcn+HSbyjc84vW7Pnq7LaHpPgpBqOutHaa3XWZr W/5JXn4Ts0RRjiQbnl6rFqMct6lrc/w2ezbWVbpYS5hVs62XsnNR9ap62QdkBH5bHz qVezcj4G9FLHPoFT9vdzw+d2AvbYpafurb4QCZfGIss493gctvno/ipg9yDTMlHiZ5 BTkbVXw5ZRnC8d8AC7YacM5Vsk4Dj6py8U942CFVad9c+3bQjFFA91UyKbUcxGm1lJ X0MSJ5w3+cOSA== Message-ID: Date: Mon, 9 Feb 2026 11:41:52 +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() From: "David Hildenbrand (Arm)" 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> <0d9cada8-7148-4a5c-a09d-120ef54559d7@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2/9/26 11:24, David Hildenbrand (Arm) wrote: > 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? On second thought, why do we pass the !inode_is_open_for_write(inode) in file_thp_enabled()? Isn't that the main problem for these memfd things? Maybe a get_write_access() is missing somewhere? -- Cheers, David