Re: [PATCH v2 07/21] crypto: shash, caam: Make use of the new sg_map helper function

[Logan Gunthorpe]

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@xxxxxxxxxxxx>
>> Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
>> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
>> ---
>>  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