Am Donnerstag, 16. März 2017, 09:39:23 CET schrieb Herbert Xu:
Hi Herbert,
> On Fri, Feb 17, 2017 at 11:31:41PM +0100, Stephan Müller wrote:
> > + } else {
> > + /* Synchronous operation */
> > + skcipher_request_set_callback(&areq->req,
> > + CRYPTO_TFM_REQ_MAY_SLEEP |
> > + CRYPTO_TFM_REQ_MAY_BACKLOG,
> > + af_alg_complete,
> > + &ctx->completion);
> > + err = af_alg_wait_for_completion(ctx->enc ?
> > + crypto_skcipher_encrypt(&areq->req) :
> > + crypto_skcipher_decrypt(&areq->req),
> > + &ctx->completion);
> > + }
>
> This is now outside of the loop for the sync case. The purpose
> of the loop in the sync case was to segment the data when we get
> a very large SG list that does not fit inside a single call.
>
> Or did I miss something?
The while loop present in the skcipher_recvmsg_sync present in the current
upstream kernel operates on ctx->rsgl. That data structure is defined as:
struct af_alg_sgl {
struct scatterlist sg[ALG_MAX_PAGES + 1];
struct page *pages[ALG_MAX_PAGES];
unsigned int npages;
};
I.e. recvmsg operates on at most 16 SGs where each can take one page of data.
Thus, if a user provides more data than 16 pages, such while loop would make
much sense.
The patch proposed here is not limited on a fixed set of 16 SGs in the RX-SGL.
The recvmsg code path allocates the required amount of SGLs space:
/* convert iovecs of output buffers into RX SGL */
while (len < ctx->used && iov_iter_count(&msg->msg_iter)) {
struct skcipher_rsgl *rsgl;
...
rsgl = sock_kmalloc(sk, sizeof(*rsgl), GFP_KERNEL);
...
struct skcipher_rsgl uses the af_alg_sgl data structure with its 16 SG
entries. But now you can have arbitrary numbers of af_alg_sgl instances up to
the memory provided by sock_kmalloc. I.e. recvmsg can now operate on multiples
of af_alg_sgl in one go.
With this approach I thought that the while loop could be a thing of the past,
considering that this is also the approach taken in skcipher_recvmsg_async
that is present in the current upstream code base.
>
> Overall I like this patch.
Thank you very much.
>
> Thanks,
Ciao
Stephan
