[PATCH] crypto: x86/chacha - Remove SIMD fallback path

Herbert Xu
2025-04-03T04:14:54Z

On Wed, Apr 02, 2025 at 08:59:34PM -0700, Eric Biggers wrote:
>
> But in a lot of cases there is also no reason to even add that restriction. I'm
> not sure why you're so eager to make the library functions harder to use.

I have no intention of making any changes to siphash. It doesn't
even use SIMD.

All I want to do is get rid of the crypto_simd_usable() fallback
paths that we currently have in arch/x86/crypto. This code is
never used in hardirq context (and should never be).

For example:

---8<---
Get rid of the fallback path as SIMD is now always usable in softirq
context.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/arch/x86/crypto/chacha_glue.c b/arch/x86/crypto/chacha_glue.c
index 8bb74a272879..6a3d60cf3192 100644
--- a/arch/x86/crypto/chacha_glue.c
+++ b/arch/x86/crypto/chacha_glue.c
@@ -6,9 +6,7 @@
* Copyright (C) 2015 Martin Willi
*/

-#include <crypto/algapi.h>
#include <crypto/internal/chacha.h>
-#include <crypto/internal/simd.h>
#include <crypto/internal/skcipher.h>
#include <linux/kernel.h>
#include <linux/module.h>
@@ -35,7 +33,6 @@ asmlinkage void chacha_4block_xor_avx512vl(u32 *state, u8 *dst, const u8 *src,
asmlinkage void chacha_8block_xor_avx512vl(u32 *state, u8 *dst, const u8 *src,
unsigned int len, int nrounds);

-static __ro_after_init DEFINE_STATIC_KEY_FALSE(chacha_use_simd);
static __ro_after_init DEFINE_STATIC_KEY_FALSE(chacha_use_avx2);
static __ro_after_init DEFINE_STATIC_KEY_FALSE(chacha_use_avx512vl);

@@ -123,23 +120,15 @@ static void chacha_dosimd(u32 *state, u8 *dst, const u8 *src,

void hchacha_block_arch(const u32 *state, u32 *stream, int nrounds)
{
- if (!static_branch_likely(&chacha_use_simd) || !crypto_simd_usable()) {
- hchacha_block_generic(state, stream, nrounds);
- } else {
- kernel_fpu_begin();
- hchacha_block_ssse3(state, stream, nrounds);
- kernel_fpu_end();
- }
+ kernel_fpu_begin();
+ hchacha_block_ssse3(state, stream, nrounds);
+ kernel_fpu_end();
}
EXPORT_SYMBOL(hchacha_block_arch);

void chacha_crypt_arch(u32 *state, u8 *dst, const u8 *src, unsigned int bytes,
int nrounds)
{
- if (!static_branch_likely(&chacha_use_simd) || !crypto_simd_usable() ||
- bytes <= CHACHA_BLOCK_SIZE)
- return chacha_crypt_generic(state, dst, src, bytes, nrounds);
-
do {
unsigned int todo = min_t(unsigned int, bytes, SZ_4K);

@@ -171,18 +160,11 @@ static int chacha_simd_stream_xor(struct skcipher_request *req,
if (nbytes < walk.total)
nbytes = round_down(nbytes, walk.stride);

- if (!static_branch_likely(&chacha_use_simd) ||
- !crypto_simd_usable()) {
- chacha_crypt_generic(state, walk.dst.virt.addr,
- walk.src.virt.addr, nbytes,
- ctx->nrounds);
- } else {
- kernel_fpu_begin();
- chacha_dosimd(state, walk.dst.virt.addr,
- walk.src.virt.addr, nbytes,
- ctx->nrounds);
- kernel_fpu_end();
- }
+ kernel_fpu_begin();
+ chacha_dosimd(state, walk.dst.virt.addr,
+ walk.src.virt.addr, nbytes,
+ ctx->nrounds);
+ kernel_fpu_end();
err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
}

@@ -207,13 +189,9 @@ static int xchacha_simd(struct skcipher_request *req)

chacha_init(state, ctx->key, req->iv);

- if (req->cryptlen > CHACHA_BLOCK_SIZE && crypto_simd_usable()) {
- kernel_fpu_begin();
- hchacha_block_ssse3(state, subctx.key, ctx->nrounds);
- kernel_fpu_end();
- } else {
- hchacha_block_generic(state, subctx.key, ctx->nrounds);
- }
+ kernel_fpu_begin();
+ hchacha_block_ssse3(state, subctx.key, ctx->nrounds);
+ kernel_fpu_end();
subctx.nrounds = ctx->nrounds;

memcpy(&real_iv[0], req->iv + 24, 8);
@@ -275,8 +253,6 @@ static int __init chacha_simd_mod_init(void)
if (!boot_cpu_has(X86_FEATURE_SSSE3))
return 0;

- static_branch_enable(&chacha_use_simd);
-
if (boot_cpu_has(X86_FEATURE_AVX) &&
boot_cpu_has(X86_FEATURE_AVX2) &&
cpu_has_xfeatures(XFEATURE_MASK_SSE | XFEATURE_MASK_YMM, NULL)) {
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt