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Subject: Re: [PATCH 0/3] add support for metadata encryption to F2FS
To:     Satya Tangirala <satyat@google.com>
CC:     "Theodore Y . Ts'o" <tytso@mit.edu>,
        Jaegeuk Kim <jaegeuk@kernel.org>,
        Eric Biggers <ebiggers@kernel.org>, Chao Yu <chao@kernel.org>,
        <linux-kernel@vger.kernel.org>, <linux-fscrypt@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>
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From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <c08aadef-47a7-f6fc-c2fa-11393ca938e8@huawei.com>
Date:   Tue, 22 Dec 2020 19:47:45 +0800
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On 2020/12/18 19:53, Satya Tangirala wrote:
> On Fri, Dec 18, 2020 at 05:02:23PM +0800, Chao Yu wrote:
>> On 2020/12/17 23:44, Satya Tangirala wrote:
>>> On Sat, Oct 10, 2020 at 05:53:06PM +0800, Chao Yu wrote:
>>>> Why not using nid as DUN, then GC could migrate encrypted node block directly via
>>>> meta inode's address space like we do for encrypted data block, rather than
>>>> decrypting node block to node page and then encrypting node page with DUN of new
>>>> blkaddr it migrates to.
>>>>
>>> The issue is, the bi_crypt_context in a bio holds a single DUN value,
>>> which is the DUN for the first data unit in the bio. blk-crypto assumes
>>> that the DUN of each subsequent data unit can be computed by simply
>>> incrementing the DUN. So physically contiguous data units can only be put
>>> into the same bio if they also have contiguous DUNs. I don't know much
>>> about nids, but if the nid is invariant w.r.t the physical block location,
>>> then there might be more fragmentation of bios in regular read/writes
>>
>> Correct, considering performance of in batch node flush, it will be better to
>> use pba as IV value.
>>
>> But, what's the plan about supporting software encryption for metadata? Current
>> f2fs write flow will handle all operations which may encounter failure before
>> allocating block address for node, if we do allocation first, and then use pba
>> as IV to encrypt node block, it will be a little complicated to revert allocation
>> if we fail to encrypt node block.
>>
> Software encryption for metadata is supported through the blk-crypto

blk-crypto will encrypt all data in filesystem, if FBE is enabled, data may
be encrypted twice?

And why not supporting hardware encryption for metadata in blk-crypto? then
both f2fs and ext4 can use inline-encryption based blk-crypto?

Thanks,

> framework - so encryption will happen in the block layer, not the
> filesystem layer. So there's nothing extra/special we need to do if
> there's an encryption failure - an encryption failure is no different
> from a read/write failure in a lower layer from f2fs' perspective.
> .
>