From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=115.124.30.98 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792713083; b=t1aSaFXBpc75i+C7xpr7IA3TE4MGuKVfQsumwJE1f+/IB/xsD5TVUpAcV+HI69D51SsE 4T1wzZ2LKk8QCmAit01muqDn6JO38xRNnwxBYyLmgP3mIdyEGcWuknJQSrqNCWAxZFchS SkSgJUJ6mDOxwuYYnN6l+n+AaZeyv5pwtD+xalXjyfj5612jonGxm7IBN9qz+rkUqxXwg 4b4eYg1waYLq2C2nyOvREflW1zjJ58lHK6VnLtiQ5O2D6v/7fHyhgJFbS/tGGNrlSIV1C OmZIfuYaSh7X029ICynr26CVHOHAqQjIgt4KA24En955Tun353YFyLH7HjdjdBXTuEw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792713083; h=DMARC-Filter:DKIM-Signature:X-Alimail-AntiSpam:Received:Message-ID: Date:MIME-Version:User-Agent:Subject:To:Cc:References: Content-Language:From:In-Reply-To:Content-Type: Content-Transfer-Encoding; bh=MWawHJcfRPvv2Lk5rcceD58Wf5MRh3mWCXal+COyIdw=; b=W/TUDbZekP0/QZULg60FivvKUXh61HOhCnXw8SIFte24KS8sy3JiZWpE31OQM++npS+F lckgfnLem1mH+mtkKSfAt3OoIGELee/SFZ4aUZHj50TZzGp0rpoSIFH481sRKG2ICnqXk Qxuvp605wwfuy1cGrmt0xOBpCGHb6UdkeMVcUgDznoJgp552P5rKmuSuvFXFMV6O7m9HU dlYCvYFRlfiIKsH8oZNSyWLjfQvDcGz5VRIp54f2g21R7q8BqAhqC9XcW0Fd4eJ5ND/ur 46mKksiZMks83ZRgI+knrQt2ndixNEHiTbCHXYaXk0HaqtwrPcyQ2ZHNoAR8b6AyAKQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass header.d=linux.alibaba.com header.i=@linux.alibaba.com header.a=rsa-sha256 header.s=default header.b=mLqVpbmZ; arc=none smtp.remote-ip=115.124.30.98 Received: from out30-98.freemail.mail.aliyun.com (out30-98.freemail.mail.aliyun.com [115.124.30.98]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9E6F0606A319; Thu, 22 Oct 2026 23:51:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 9E6F0606A319 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.a=rsa-sha256 header.s=default header.b=mLqVpbmZ DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1792713078; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=MWawHJcfRPvv2Lk5rcceD58Wf5MRh3mWCXal+COyIdw=; b=mLqVpbmZM9f+bl/2zAzq44rmFgB9wnuLIUQ1rtRMtP+j2cDnXht9ChCfaf/O9US2ZJVQSMFGgvFk0Olv94jyGyeZofbT3aCkYsD4YaaEDGR7b2zoSGstpDCejz95PTKM2ED2Cg/U4C8Iucs5WwiEkL6iusqoPvEHb+wWbdG05Fs= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R151e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045133197;MF=libaokun@linux.alibaba.com;NM=1;PH=DS;RN=18;SR=0;TI=SMTPD_---0XDKE1xm_1792713075; Received: from 30.170.203.187(mailfrom:libaokun@linux.alibaba.com fp:SMTPD_---0XDKE1xm_1792713075 cluster:ay36) by smtp.aliyun-inc.com; Fri, 23 Oct 2026 07:51:16 +0800 Message-ID: Date: Fri, 23 Oct 2026 07:51:15 +0800 X-Mailing-List: linux-xfs@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 00/13] block, ext4: allow encryption with a block size larger than the page size To: Eric Biggers Cc: linux-ext4@vger.kernel.org, linux-fscrypt@vger.kernel.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, jaegeuk@kernel.org, axboe@kernel.dk, hch@lst.de, djwong@kernel.org, brauner@kernel.org, tytso@mit.edu, berto@igalia.com, adilger.kernel@dilger.ca, jack@suse.cz, yi.zhang@huawei.com, ojaswin@linux.ibm.com, ritesh.list@gmail.com References: <20261011170958.1759230-1-libaokun@linux.alibaba.com> <20261015185325.GG2170687@google.com> <625e5190-d43e-4a2b-9296-da15c52d1a9a@linux.alibaba.com> <20261022220454.GC1383716@google.com> Content-Language: en-US From: Baokun Li In-Reply-To: <20261022220454.GC1383716@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 2026/10/23 06:04, Eric Biggers wrote: > On Fri, Oct 23, 2026 at 12:30:39AM +0800, Baokun Li wrote: >> Hi Eric, Thank you for your feedback! >> On 2026/10/16 02:53, Eric Biggers wrote: >>> On Mon, Oct 12, 2026 at 01:09:45AM +0800, Baokun Li wrote: >>>> Motivation >>>> ========== >>>> >>>> ext4 supports a block size larger than the page size (LBS), e.g. a 32k >>>> block size on a machine with 4k pages [1]. Encryption, however, is >>>> still refused on such a filesystem: file contents used to be encrypted >>>> page by page in the fs-layer path, which cannot handle a folio that >>>> covers several data units, so the checks that refuse encryption with >>>> such a block size stayed in place. >>>> >>>> Since commit 5acc6f649a68 ("fscrypt: Always use blk-crypto for >>>> contents on block-based filesystems") file contents are always >>>> encrypted through blk-crypto. Inline encryption hardware can already >>>> en/decrypt a data unit that spans several pages, but the fallback and >>>> the block layer cannot carry such a data unit: >>>> >>>> 1. blk-crypto-fallback en/decrypts a data unit with the bio_vecs of >>>> a single page-clamped segment, so a larger data unit fails with >>>> BLK_STS_INVAL; >>>> 2. the block layer requires every bio_vec of an encrypted bio to be >>>> data unit aligned, and splits such a bio without rounding the >>>> split size down to the data unit size; >>>> 3. iomap cuts the direct I/O bios of an encrypted file only at the >>>> logical block size of the device, so a bio can end in the middle >>>> of a data unit. >>>> >>>> This series adds the missing pieces on all three layers, removes the >>>> refusals, and enables large folios for encrypted files on the way. >>>> >>>> [1]: https://lore.kernel.org/all/20251121090654.631996-1-libaokun@huaweicloud.com >>> A high-level question: most of the complexity in this series is to >>> support crypto_data_unit_size > PAGE_SIZE, despite the actual goal being >>> to support fs_block_size > PAGE_SIZE. It's left unstated that the >>> default of crypto_data_unit_size == fs_block_size is used. However, >>> ext4 and f2fs already support crypto_data_unit_size < fs_block_size. >>> >>> Would leaving the crypto_data_unit_size at e.g. 4 KiB while increasing >>> fs_block_size be a simpler way to achieve the goal of this series? >> I initially followed the LBS approach of lifting the page-size >> restriction, keeping the existing default crypto_data_unit_size >> equal to fs_block_size. I had not considered using sub-block DUs. >> >> After your reply, I implemented a variant using min(bs, PS) for >> new default v2 policies, recording a smaller DU explicitly on disk. >> This avoids patches 3-6 and the per-bvec alignment relaxation in >> patch 10, and is indeed much simpler. >> >> Both variants retain large-folio support and showed similar gains, >> about twice their respective 4K-block controls. Although 32K DUs reduced >> decryption calls eightfold, I did not observe a consistent additional >> throughput benefit, or CPU savings at matched bandwidth, in the tested >> workloads. >> >>> Or do you feel that would be incomplete, and you'd indeed like to >>> support crypto_data_unit_size = fs_block_size > PAGE_SIZE? >> However, keeping DU = bs has a compatibility advantage for existing >> encrypted filesystems. >> >> For example, a 64K-block filesystem created with a default v2 policy >> on a 64K-page machine uses 64K DUs. Supporting DU > PAGE_SIZE would >> allow a 4K-page machine to use that format without re-encryption, >> assuming the other policy and backend requirements are met. >> >> This also covers otherwise-supported legacy v1 policies, which cannot >> encode smaller DUs. >> >> Explicit 4K v2 DUs can also be portable across page sizes, but >> choosing a smaller DU for new files does not make existing large-DU >> ciphertext readable on a smaller-page machine. I have not yet tested >> the cross-page-size migration. >> >> If you think supporting DU = bs > PS makes this series too broad, >> I can use the simpler sub-block version in the next revision and >> develop larger-DU support separately. >> >> Looking forward to hearing your thoughts. > I think I prefer the simpler version for now. If someone wants to > create encrypted files on a 64K block size filesystem on a 64K PAGE_SIZE > system that are also readable on a 4K PAGE_SIZE system, for now they can > just set crypto_data_unit_size = 4K. v1 policies were deprecated 7 > years ago, so they shouldn't really factor into considerations here. > > Note also that setting crypto_data_unit_size too high can break write > atomicity as well as compatibility with inline encryption hardware. > > (Also, the more common use case these days is that someone is > *increasing* their page size, not decreasing it.) > > I understand there's been a trend to lift limitations like these and > make every size work on every system. But the large crypto data unit > sizes are difficult to implement correctly, and the proposed > implementation slows down common cases that matter. Let's focus on > fs_block_size > PAGE_SIZE by itself first. Agreed, that makes sense. I'll switch to sub-block data units in the next revision. Thank you for your feedback! Cheers, Baokun