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

[Yongseok Koh <yskoh@mellanox.com>]

On Fri, May 03, 2019 at 03:54:09AM +0000, Honnappa Nagarahalli wrote:
> > >>> 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
> > >
> > > The default image is 8.1 spec and except octeontx2 every other SoC is
> I am not following this. I think the default image is 8.0.
> 
> > > 8.1 and For octeotx2 crypto is supported. If so, Should we worry this case?
> I assume we all are talking about the distro/binary portable build. IMO, we should not just look at the existing SoCs.
> The CPU specific builds have the freedom to compile as per their corresponding support.
> 
> > 
> > Right, it sounds to me that we can disable the option without having the new
> > config flag until such instructions get needed. According to gcc-8 release note
> > [1], currently '+crypto' implies '+aes' and '+sha2' while '+sha3' and '+sm4' are
> > newly introduced. Given that armv8 crypto PMD uses external binary of
> > Marvell. I don't see any reason to enable '+crypto'. How about simply disable
> > it from armv8 build configs?
> I think it should be fine. But, this alone is not enough. The run time
> detection of the crypto feature and hooking up the correct pointers needs to
> be added.

Like Jerin pointed out above, armv8 cryptodev already has runtime check of
cpuflags. If there's no support, it returns error. Unless we need a fallback
function with non-crypto instructions instead of returning error, I don't think
such hookup of func pointers are needed.

> > diff --git a/config/arm/meson.build b/config/arm/meson.build index
> > 7fa6ed3105..abc8cf346c 100644
> > --- a/config/arm/meson.build
> > +++ b/config/arm/meson.build
> > @@ -74,7 +74,7 @@ flags_octeontx2_extra = [
> >         ['RTE_USE_C11_MEM_MODEL', true]]
> > 
> >  machine_args_generic = [
> > -       ['default', ['-march=armv8-a+crc+crypto']],
> > +       ['default', ['-march=armv8-a+crc']],
> >         ['native', ['-march=native']],
> >         ['0xd03', ['-mcpu=cortex-a53']],
> >         ['0xd04', ['-mcpu=cortex-a35']], diff --git
> > a/mk/machine/armv8a/rte.vars.mk b/mk/machine/armv8a/rte.vars.mk index
> > 8252efbb7b..5e3ffc3adf 100644
> > --- a/mk/machine/armv8a/rte.vars.mk
> > +++ b/mk/machine/armv8a/rte.vars.mk
> > @@ -28,4 +28,4 @@
> >  # CPU_LDFLAGS =
> >  # CPU_ASFLAGS =
> > 
> > -MACHINE_CFLAGS += -march=armv8-a+crc+crypto
> > +MACHINE_CFLAGS += -march=armv8-a+crc
> > 
> > 
> > [1] https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.gnu.org%2Fgcc-8%2Fchanges.html&amp;data=02%7C01%7Cyskoh%40mellanox.com%7C5cd398e4cf1e45c1755a08d6cf7b0091%7Ca652971c7d2e4d9ba6a4d149256f461b%7C0%7C0%7C636924524543262594&amp;sdata=4m4S2VQUVBMLYqpxmeLoAPqAcKGm9u1Wo5R7oE2CK94%3D&amp;reserved=0
> > 
> > Thanks,
> > Yongseok
> > 
> > >> enabled, compiler can generate 3-way exclusive OR instructions beyond
> > >> the intrinsics.
> > >
> > > The very same problem will be applicable for Linux kernel too for
> > distribution binary case.
> > > If the above statement is true about 8.2 crypto and crypto generation
> > > without Intrinsics then we need to see how linux kernel handling that
> > > and align our solution based on that.
> Yes, the compiler team cited Linux kernel example, I have not verified it myself.
> 
> > >
> > >> 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
> > >
> > > Not sure how it helps? If we know the compiler is generating a
> > > specific function With crypto instruction then we can generate
> > > _alternative_ function for the same With hwcap?.How do we know which
> > > function compiler using compiler instructions?
> This feature is similar to using function pointers and choosing which function
> pointer to use at run time. If this feature is used, the function pointer to
> use is decided during dynamic linking stage.

I think what Jerin meant was about the case where compiler can generate crypto
instructions beyond intrinsics/asm like sha3 for 3-way exclusive OR
instructions. In this case, such function pointer can't help as we can't know
how compiler generates such instructions.

> Either ways, we need to have 2 sets of crypto PMD drivers. One that implements
> the actual functionality using crypto intrinsics/assembly. Only, this code
> needs to be compiled with '+crypto'. Second driver that implements just stubs
> and returns error. This code will be compiled without '+crypto'. At run time,
> depending on the HWCAP, the correct driver/function pointers need to be hooked
> up.

Like I mentioned above, it may not be necessary. armv8 cryptodev links external
library, which is compiled separately (out of dpdk) with crypto support and we
don't have/need a fallback but returns error if no crypto support in runtime.

> > >> sure on GNU indirect function portability.
> > >
> > > We are using HWCAP scheme, So we may not need the very exact GNU
> > > indirect scheme to fix the issue.
> Agree, using indirect functions is not a must.
> 
> > >
> > >>
> > >> [1]
> > >> https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwil
> > >> lnewton.name%2F2013%2F07%2F02%2Fusing-gnu-indirect-
> > functions%2F&amp;d
> > >>
> > ata=02%7C01%7Cyskoh%40mellanox.com%7Cda8fb7ed03e7406ded8908d6c
> > ee6d759
> > >> %7Ca652971c7d2e4d9ba6a4d149256f461b%7C0%7C0%7C63692388818
> > 9316743&amp;
> > >>
> > sdata=x5XNd5WZ3EtiprPMiFzaskvigX8K0AoXA2w%2BKiN156c%3D&amp;res
> > erved=0