linux-kernel - Re: [PATCH v2 07/21] crypto: shash, caam: Make use of the new sg

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Date:   Thu, 27 Apr 2017 09:45:57 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-raid@...r.kernel.org,
        linux-mmc@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-scsi@...r.kernel.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,
        dm-devel@...hat.com, Christoph Hellwig <hch@....de>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        Jens Axboe <axboe@...nel.dk>,
        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>,
        Stephen Bates <sbates@...thlin.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v2 07/21] crypto: shash, caam: Make use of the new sg_map
 helper function



On 26/04/17 09:56 PM, Herbert Xu wrote:
> On Tue, Apr 25, 2017 at 12:20:54PM -0600, Logan Gunthorpe wrote:
>> Very straightforward conversion to the new function in the caam driver
>> and shash library.
>>
>> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
>> Cc: Herbert Xu <herbert@...dor.apana.org.au>
>> Cc: "David S. Miller" <davem@...emloft.net>
>> ---
>>  crypto/shash.c                | 9 ++++++---
>>  drivers/crypto/caam/caamalg.c | 8 +++-----
>>  2 files changed, 9 insertions(+), 8 deletions(-)
>>
>> diff --git a/crypto/shash.c b/crypto/shash.c
>> index 5e31c8d..5914881 100644
>> --- a/crypto/shash.c
>> +++ b/crypto/shash.c
>> @@ -283,10 +283,13 @@ int shash_ahash_digest(struct ahash_request *req, struct shash_desc *desc)
>>  	if (nbytes < min(sg->length, ((unsigned int)(PAGE_SIZE)) - offset)) {
>>  		void *data;
>>  
>> -		data = kmap_atomic(sg_page(sg));
>> -		err = crypto_shash_digest(desc, data + offset, nbytes,
>> +		data = sg_map(sg, 0, SG_KMAP_ATOMIC);
>> +		if (IS_ERR(data))
>> +			return PTR_ERR(data);
>> +
>> +		err = crypto_shash_digest(desc, data, nbytes,
>>  					  req->result);
>> -		kunmap_atomic(data);
>> +		sg_unmap(sg, data, 0, SG_KMAP_ATOMIC);
>>  		crypto_yield(desc->flags);
>>  	} else
>>  		err = crypto_shash_init(desc) ?:
> 
> Nack.  This is an optimisation for the special case of a single
> SG list entry.  In fact in the common case the kmap_atomic should
> disappear altogether in the no-highmem case.  So replacing it
> with sg_map is not acceptable.

What you seem to have missed is that sg_map is just a thin wrapper
around kmap_atomic. Perhaps with a future check for a mappable page.
This change should have zero impact on performance.

Logan