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From 2d3b6fae7d1a2ad821769440daa91d7eec5c8250 Mon Sep 17 00:00:00 2001
From: Eneas U de Queiroz <cotequeiroz@gmail.com>
Date: Fri, 20 Dec 2019 09:41:44 -0300
Subject: [PATCH] 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: Eneas U de Queiroz <cotequeiroz@gmail.com>
--- a/drivers/crypto/Kconfig
+++ b/drivers/crypto/Kconfig
@@ -585,6 +585,29 @@ config CRYPTO_DEV_QCE
hardware. To compile this driver as a module, choose M here. The
module will be called qcrypto.
+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
--- a/drivers/crypto/qce/skcipher.c
+++ b/drivers/crypto/qce/skcipher.c
@@ -13,6 +13,7 @@
#include <linux/device.h>
#include <linux/interrupt.h>
+#include <linux/moduleparam.h>
#include <linux/types.h>
#include <crypto/aes.h>
#include <crypto/des.h>
@@ -20,6 +21,13 @@
#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)
@@ -170,15 +178,7 @@ static int qce_skcipher_setkey(struct cr
if (!key || !keylen)
return -EINVAL;
- if (IS_AES(flags)) {
- switch (IS_XTS(flags) ? keylen >> 1 : keylen) {
- case AES_KEYSIZE_128:
- case AES_KEYSIZE_256:
- break;
- default:
- goto fallback;
- }
- } else if (IS_DES(flags)) {
+ if (IS_DES(flags)) {
u32 tmp[DES_EXPKEY_WORDS];
ret = des_ekey(tmp, key);
@@ -189,8 +189,8 @@ static int qce_skcipher_setkey(struct cr
ctx->enc_keylen = keylen;
memcpy(ctx->enc_key, key, keylen);
- return 0;
-fallback:
+ if (!IS_AES(flags))
+ return 0;
ret = crypto_skcipher_setkey(ctx->fallback, key, keylen);
if (!ret)
ctx->enc_keylen = keylen;
@@ -213,8 +213,9 @@ static int qce_skcipher_crypt(struct skc
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)) {
SKCIPHER_REQUEST_ON_STACK(subreq, ctx->fallback);
skcipher_request_set_tfm(subreq, ctx->fallback);
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