From: Eric Biggers <ebiggers@xxxxxxxxxx> Improve some of the comments in aes-xts-avx-x86_64.S. Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> --- arch/x86/crypto/aes-xts-avx-x86_64.S | 31 ++++++++++++++++++---------- 1 file changed, 20 insertions(+), 11 deletions(-) diff --git a/arch/x86/crypto/aes-xts-avx-x86_64.S b/arch/x86/crypto/aes-xts-avx-x86_64.S index ca69e6480cb6..903b894e5f48 100644 --- a/arch/x86/crypto/aes-xts-avx-x86_64.S +++ b/arch/x86/crypto/aes-xts-avx-x86_64.S @@ -341,13 +341,18 @@ .endif .endm // Do one step in computing the next set of tweaks using the VPCLMULQDQ method // (the same method _next_tweakvec uses for VL > 16). This means multiplying -// each tweak by x^(4*VL/16) independently. Since 4*VL/16 is a multiple of 8 -// when VL > 16 (which it is here), the needed shift amounts are byte-aligned, -// which allows the use of vpsrldq and vpslldq to do 128-bit wide shifts. +// each tweak by x^(4*VL/16) independently. +// +// Since 4*VL/16 is a multiple of 8 when VL > 16 (which it is here), the needed +// shift amounts are byte-aligned, which allows the use of vpsrldq and vpslldq +// to do 128-bit wide shifts. The 128-bit left shift (vpslldq) saves +// instructions directly. The 128-bit right shift (vpsrldq) performs better +// than a 64-bit right shift on Intel CPUs in the context where it is used here, +// because it runs on a different execution port from the AES instructions. .macro _tweak_step_pclmul i .if \i == 0 vpsrldq $(128 - 4*VL/16) / 8, TWEAK0, NEXT_TWEAK0 .elseif \i == 2 vpsrldq $(128 - 4*VL/16) / 8, TWEAK1, NEXT_TWEAK1 @@ -378,11 +383,11 @@ // _tweak_step does one step of the computation of the next set of tweaks from // TWEAK[0-3]. To complete all steps, this is invoked with increasing values of // \i that include at least 0 through 19, then 1000 which signals the last step. // // This is used to interleave the computation of the next set of tweaks with the -// AES en/decryptions, which increases performance in some cases. +// AES en/decryptions, which increases performance in some cases. Clobbers V5. .macro _tweak_step i .if VL == 16 _tweak_step_mulx \i .else _tweak_step_pclmul \i @@ -415,13 +420,14 @@ // easy to do AES-128 and AES-192 by skipping irrelevant rounds at the // beginning. Skipping rounds at the end doesn't work as well because // the last round needs different instructions. // // An alternative approach would be to roll up all the round loops. We - // don't do that because it isn't compatible with caching the round keys - // in registers which we do when possible (see below), and also because - // it seems unwise to rely *too* heavily on the CPU's branch predictor. + // don't do that because (a) it isn't compatible with caching the round + // keys in registers which we do when possible (see below), (b) we + // interleave the AES rounds with the XTS tweak computation, and (c) it + // seems unwise to rely *too* heavily on the CPU's branch predictor. lea OFFS-16(KEY, KEYLEN64, 4), KEY // If all 32 SIMD registers are available, cache all the round keys. .if USE_AVX10 cmp $24, KEYLEN @@ -482,11 +488,11 @@ .endm // Do a single round of AES en/decryption on the blocks in registers V0-V3, // using the same key for all blocks. The round key is loaded from the // appropriate register or memory location for round \i. In addition, does two -// steps of the computation of the next set of tweaks. May clobber V4. +// steps of the computation of the next set of tweaks. May clobber V4 and V5. .macro _vaes_4x enc, last, i .if USE_AVX10 _tweak_step (2*(\i-5)) _vaes \enc, \last, KEY\i, V0 _vaes \enc, \last, KEY\i, V1 @@ -725,10 +731,13 @@ jmp .Ldone\@ .endm // void aes_xts_encrypt_iv(const struct crypto_aes_ctx *tweak_key, // u8 iv[AES_BLOCK_SIZE]); +// +// Encrypt |iv| using the AES key |tweak_key| to get the first tweak. Assumes +// that the CPU supports AES-NI and AVX, but not necessarily VAES or AVX10. SYM_TYPED_FUNC_START(aes_xts_encrypt_iv) .set TWEAK_KEY, %rdi .set IV, %rsi .set KEYLEN, %eax .set KEYLEN64, %rax @@ -755,13 +764,13 @@ SYM_TYPED_FUNC_START(aes_xts_encrypt_iv) SYM_FUNC_END(aes_xts_encrypt_iv) // Below are the actual AES-XTS encryption and decryption functions, // instantiated from the above macro. They all have the following prototype: // -// void (*xts_asm_func)(const struct crypto_aes_ctx *key, -// const u8 *src, u8 *dst, unsigned int len, -// u8 tweak[AES_BLOCK_SIZE]); +// void (*xts_crypt_func)(const struct crypto_aes_ctx *key, +// const u8 *src, u8 *dst, unsigned int len, +// u8 tweak[AES_BLOCK_SIZE]); // // |key| is the data key. |tweak| contains the next tweak; the encryption of // the original IV with the tweak key was already done. This function supports // incremental computation, but |len| must always be >= 16 (AES_BLOCK_SIZE), and // |len| must be a multiple of 16 except on the last call. If |len| is a -- 2.47.1
