[PATCH 1/2] crypto: DRBG - eliminate constant reinitialization of SGL

[Stephan Müller]

The CTR DRBG requires two SGLs pointing to input/output buffers for the
CTR AES operation. The used SGLs always have only one entry. Thus, the
SGL can be initialized during allocation time, preventing a
re-initialization of the SGLs during each call.

The performance is increased by about 1 to 3 percent depending on the
size of the requested buffer size.

Signed-off-by: Stephan Mueller <smuel...@chronox.de>
---
 crypto/drbg.c         | 11 +++++++----
 include/crypto/drbg.h |  1 +
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/crypto/drbg.c b/crypto/drbg.c
index 466a112a4446..ee302fd229ad 100644
--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -1715,6 +1715,9 @@ static int drbg_init_sym_kernel(struct drbg_state *drbg)
        drbg->outscratchpad = (u8 *)PTR_ALIGN(drbg->outscratchpadbuf,
                                              alignmask + 1);
 
+       sg_init_table(&drbg->sg_in, 1);
+       sg_init_table(&drbg->sg_out, 1);
+
        return alignmask;
 }
 
@@ -1743,17 +1746,17 @@ static int drbg_kcapi_sym_ctr(struct drbg_state *drbg,
                              u8 *inbuf, u32 inlen,
                              u8 *outbuf, u32 outlen)
 {
-       struct scatterlist sg_in, sg_out;
+       struct scatterlist *sg_in = &drbg->sg_in, *sg_out = &drbg->sg_out;
        int ret;
 
-       sg_init_one(&sg_in, inbuf, inlen);
-       sg_init_one(&sg_out, drbg->outscratchpad, DRBG_OUTSCRATCHLEN);
+       sg_set_buf(sg_in, inbuf, inlen);
+       sg_set_buf(sg_out, drbg->outscratchpad, DRBG_OUTSCRATCHLEN);
 
        while (outlen) {
                u32 cryptlen = min3(inlen, outlen, (u32)DRBG_OUTSCRATCHLEN);
 
                /* Output buffer may not be valid for SGL, use scratchpad */
-               skcipher_request_set_crypt(drbg->ctr_req, &sg_in, &sg_out,
+               skcipher_request_set_crypt(drbg->ctr_req, sg_in, sg_out,
                                           cryptlen, drbg->V);
                ret = crypto_wait_req(crypto_skcipher_encrypt(drbg->ctr_req),
                                        &drbg->ctr_wait);
diff --git a/include/crypto/drbg.h b/include/crypto/drbg.h
index 8f941102af36..54b9f5d375f5 100644
--- a/include/crypto/drbg.h
+++ b/include/crypto/drbg.h
@@ -127,6 +127,7 @@ struct drbg_state {
        __u8 *outscratchpadbuf;                 /* CTR mode output scratchpad */
         __u8 *outscratchpad;                   /* CTR mode aligned outbuf */
        struct crypto_wait ctr_wait;            /* CTR mode async wait obj */
+       struct scatterlist sg_in, sg_out;       /* CTR mode SGLs */
 
        bool seeded;            /* DRBG fully seeded? */
        bool pr;                /* Prediction resistance enabled? */
-- 
2.17.1