crypto: x86/chacha20 - Add a 8-block AVX-512VL variant
This variant is similar to the AVX2 version, but benefits from the AVX-512 rotate instructions and the additional registers, so it can operate without any data on the stack. It uses ymm registers only to avoid the massive core throttling on Skylake-X platforms. Nontheless does it bring a ~30% speed improvement compared to the AVX2 variant for random encryption lengths. The AVX2 version uses "rep movsb" for partial block XORing via the stack. With AVX-512, the new "vmovdqu8" can do this much more efficiently. The associated "kmov" instructions to work with dynamic masks is not part of the AVX-512VL instruction set, hence we depend on AVX-512BW as well. Given that the major AVX-512VL architectures provide AVX-512BW and this extension does not affect core clocking, this seems to be no problem at least for now. Signed-off-by:Martin Willi <martin@strongswan.org> Signed-off-by:
Herbert Xu <herbert@gondor.apana.org.au>
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