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

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Message-ID: <20170427035603.GA32212@gondor.apana.org.au>
Date:   Thu, 27 Apr 2017 11:56:03 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Logan Gunthorpe <logang@...tatee.com>
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 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.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt