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

Logan Gunthorpe
2017-04-27T15:45:57Z

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-OTvnGxWRz7hWk0Htik3J/w@public.gmane.org>
>> Cc: Herbert Xu <herbert-lOAM2aK0SrRLBo1qDEOMRrpzq4S04n8Q@public.gmane.org>
>> Cc: "David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>
>> ---
>> 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