linux-kernel - Re: [PATCH 09/22] dm-crypt: Make use of the new sg

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Date:   Fri, 14 Apr 2017 10:03:43 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Christoph Hellwig <hch@....de>
Cc:     "Martin K. Petersen" <martin.petersen@...cle.com>,
        Sagi Grimberg <sagi@...mberg.me>, Jens Axboe <axboe@...nel.dk>,
        Tejun Heo <tj@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Ming Lin <ming.l@....samsung.com>,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, intel-gfx@...ts.freedesktop.org,
        linux-raid@...r.kernel.org, linux-mmc@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-nvdimm@...ts.01.org,
        linux-scsi@...r.kernel.org, fcoe-devel@...n-fcoe.org,
        open-iscsi@...glegroups.com, megaraidlinux.pdl@...adcom.com,
        sparmaintainer@...sys.com, devel@...verdev.osuosl.org,
        target-devel@...r.kernel.org, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, rds-devel@....oracle.com,
        Steve Wise <swise@...ngridcomputing.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [PATCH 09/22] dm-crypt: Make use of the new sg_map helper in 4
 call sites



On 14/04/17 02:39 AM, Christoph Hellwig wrote:
> On Thu, Apr 13, 2017 at 04:05:22PM -0600, Logan Gunthorpe wrote:
>> Very straightforward conversion to the new function in all four spots.
> 
> I think the right fix here is to switch dm-crypt to the ahash API
> that takes a scatterlist.

Hmm, well I'm not sure I understand the code enough to make that
conversion. But I was looking at it. One tricky bit seems to be that
crypt_iv_lmk_one adds a seed, skips the first 16 bytes in the page and
then hashes another 16 bytes from other data. What would you do
construct a new sgl for it and pass it to the ahash api?

The other thing is crypt_iv_lmk_post also seems to modify the page after
the hash with a  crypto_xor so you'd still need at least one kmap in there.

Logan