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crypto: qce - use AES fallback for small requests

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Process small blocks using the fallback cipher, as a workaround for an
observed failure (DMA-related, apparently) when computing the GCM ghash
key.  This brings a speed gain as well, since it avoids the latency of
using the hardware engine to process small blocks.

Using software for all 16-byte requests would be enough to make GCM
work, but to increase performance, a larger threshold would be better.
Measuring the performance of supported ciphers with openssl speed,
software matches hardware at around 768-1024 bytes.

Considering the 256-bit ciphers, software is 2-3 times faster than qce
at 256-bytes, 30% faster at 512, and about even at 768-bytes.  With
128-bit keys, the break-even point would be around 1024-bytes.

This adds the 'aes_sw_max_len' parameter, to set the largest request
length processed by the software fallback.  Its default is being set to
512 bytes, a little lower than the break-even point, to balance the cost
in CPU usage.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Eneas U de Queiroz 2020-02-07 12:02:26 -03:00 committed by Herbert Xu
parent d6364b8128
commit ce163ba0bf
2 changed files with 35 additions and 8 deletions
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23
drivers/crypto/Kconfig
View file

@ -685,6 +685,29 @@ choice
endchoice
config CRYPTO_DEV_QCE_SW_MAX_LEN
int "Default maximum request size to use software for AES"
depends on CRYPTO_DEV_QCE && CRYPTO_DEV_QCE_SKCIPHER
default 512
help
This sets the default maximum request size to perform AES requests
using software instead of the crypto engine. It can be changed by
setting the aes_sw_max_len parameter.
Small blocks are processed faster in software than hardware.
Considering the 256-bit ciphers, software is 2-3 times faster than
qce at 256-bytes, 30% faster at 512, and about even at 768-bytes.
With 128-bit keys, the break-even point would be around 1024-bytes.
The default is set a little lower, to 512 bytes, to balance the
cost in CPU usage. The minimum recommended setting is 16-bytes
(1 AES block), since AES-GCM will fail if you set it lower.
Setting this to zero will send all requests to the hardware.
Note that 192-bit keys are not supported by the hardware and are
always processed by the software fallback, and all DES requests
are done by the hardware.
config CRYPTO_DEV_QCOM_RNG
tristate "Qualcomm Random Number Generator Driver"
depends on ARCH_QCOM || COMPILE_TEST

20
drivers/crypto/qce/skcipher.c
View file

@ -5,6 +5,7 @@
#include <linux/device.h>
#include <linux/interrupt.h>
#include <linux/moduleparam.h>
#include <linux/types.h>
#include <crypto/aes.h>
#include <crypto/internal/des.h>
@ -12,6 +13,13 @@
#include "cipher.h"
static unsigned int aes_sw_max_len = CONFIG_CRYPTO_DEV_QCE_SW_MAX_LEN;
module_param(aes_sw_max_len, uint, 0644);
MODULE_PARM_DESC(aes_sw_max_len,
"Only use hardware for AES requests larger than this "
"[0=always use hardware; anything <16 breaks AES-GCM; default="
__stringify(CONFIG_CRYPTO_DEV_QCE_SOFT_THRESHOLD)"]");
static LIST_HEAD(skcipher_algs);
static void qce_skcipher_done(void *data)
@ -166,15 +174,10 @@ static int qce_skcipher_setkey(struct crypto_skcipher *ablk, const u8 *key,
switch (IS_XTS(flags) ? keylen >> 1 : keylen) {
case AES_KEYSIZE_128:
case AES_KEYSIZE_256:
memcpy(ctx->enc_key, key, keylen);
break;
default:
goto fallback;
}
ctx->enc_keylen = keylen;
memcpy(ctx->enc_key, key, keylen);
return 0;
fallback:
ret = crypto_sync_skcipher_setkey(ctx->fallback, key, keylen);
if (!ret)
ctx->enc_keylen = keylen;
@ -224,8 +227,9 @@ static int qce_skcipher_crypt(struct skcipher_request *req, int encrypt)
rctx->flags |= encrypt ? QCE_ENCRYPT : QCE_DECRYPT;
keylen = IS_XTS(rctx->flags) ? ctx->enc_keylen >> 1 : ctx->enc_keylen;
if (IS_AES(rctx->flags) && keylen != AES_KEYSIZE_128 &&
keylen != AES_KEYSIZE_256) {
if (IS_AES(rctx->flags) &&
((keylen != AES_KEYSIZE_128 && keylen != AES_KEYSIZE_256) ||
req->cryptlen <= aes_sw_max_len)) {
SYNC_SKCIPHER_REQUEST_ON_STACK(subreq, ctx->fallback);
skcipher_request_set_sync_tfm(subreq, ctx->fallback);