Commit ce163ba0 authored by Eneas U de Queiroz's avatar Eneas U de Queiroz Committed by Herbert Xu
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crypto: qce - use AES fallback for small requests 



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: default avatarEneas U de Queiroz <cotequeiroz@gmail.com>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent d6364b81

drivers/crypto/Kconfig

+23 −0
Original line number Diff line number Diff line
@@ -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

drivers/crypto/qce/skcipher.c

+12 −8
Original line number Diff line number Diff line
@@ -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);