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

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

> >> 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.

> 
> Thanks,
> Yongseok
>