Re: [dpdk-dev] [EXT] [PATCH 5/6] build: add option for armv8 crypto extension

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

> On Apr 15, 2019, at 1:13 PM, Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com> wrote:
> 
> >>>> Subject: [EXT] [PATCH 5/6] build: add option for armv8 crypto
> >>>> extension
> >>>>
> >>>> CONFIG_RTE_MACHINE="armv8a"
> >>>> +CONFIG_RTE_ENABLE_ARMV8_CRYPTO=y
> >>>
> >>> This approach is not scalable. Even, it is not good for BlueField as
> >>> you you need to maintain two images.
> >>>
> >>> Unlike other CPU flags, arm64's crypto cpu flag is really _optional_.
> >>> Access to crypto instructions is always at under runtime check.
> >>> See the following in rte_armv8_pmd.c
> >>>
> >>>
> >>>    /* Check CPU for support for AES instruction set */
> >>>    if (!rte_cpu_get_flag_enabled(RTE_CPUFLAG_AES)) {
> >>>        ARMV8_CRYPTO_LOG_ERR(
> >>>            "AES instructions not supported by CPU");
> >>>        return -EFAULT;
> >>>    }
> >>>
> >>>    /* Check CPU for support for SHA instruction set */
> >>>    if (!rte_cpu_get_flag_enabled(RTE_CPUFLAG_SHA1) ||
> >>>        !rte_cpu_get_flag_enabled(RTE_CPUFLAG_SHA2)) {
> >>>        ARMV8_CRYPTO_LOG_ERR(
> >>>            "SHA1/SHA2 instructions not supported by CPU");
> >>>        return -EFAULT;
> >>>    }
> >>>
> >>> So In order to avoid one more config flags specific to armv8 in
> >>> meson and makefile build infra And avoid the need for 6/6 patch.
> >>> IMO, # Introduce optional CPU flag scheme in eal. Treat armv8 crypto
> >>> as optional flag # Skip the eal init check for optional flag.
> >>>
> >>> Do you see any issues with that approach?
> >>
> >> I also thought about that approach and that was my number 1 priority.
> >> But, I had one question came to my mind. Maybe, arm people can
> >> confirm it. Is it 100% guaranteed that compiler never makes use of
> >> any of crypto instructions even if there's no specific asm/intrinsic
> >> code?  The crypto extension has aes, pmull,
> >> sha1 and sha2. In case of rte_memcpy() for x86, for example, compiler
> >> may optimize code using avx512f instructions even though it is
> >> written specifically with avx2 intrinsics (__mm256_*) unless avx512f is
> disabled.
> >>
> >> If a complier expert in arm (or anyone else) confirm it is completely
> >> **optional**, then I'd love to take that approach for sure.
> >>
> >> Copied dpdk-on-arm ML.
> >>
> > I do not know the answer, will have to check with the compiler team. I will get
> back on this.
> 
> Any update yet?
Currently, enabling 'crypto' flag will generate the crypto instructions only when crypto intrinsics are used. However, when 'sha3' (part of 8.2 crypto) flag is enabled, compiler can generate 3-way exclusive OR instructions beyond the intrinsics. Compiler team cannot provide a guarantee that other crypto instructions will not be used beyond the intrinsics.

The current suggestion is to use GNU indirect function [1] or similar. I am not sure on GNU indirect function portability.

[1] https://willnewton.name/2013/07/02/using-gnu-indirect-functions/

> 
> Thanks
> Yongseok