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

Herbert Xu
2017-04-28T06:30:39Z

On Thu, Apr 27, 2017 at 09:45:57AM -0600, Logan Gunthorpe wrote:
>
>
> 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.

You are right. Indeed the existing code looks buggy as they
don't take sg->offset into account when doing the kmap. Could
you send me some patches that fix these problems first so that
they can be easily backported?

Thanks,
--
Email: Herbert Xu <herbert-lOAM2aK0SrRLBo1qDEOMRrpzq4S04n8Q@public.gmane.org>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt