linux-kernel - Re: [PATCH 07/15] s390/crc32: expose CRC32 functions through lib

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Message-ID: <20241021104007.6950-E-hca@linux.ibm.com>
Date: Mon, 21 Oct 2024 12:40:07 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: Eric Biggers <ebiggers@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-crypto@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-mips@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        loongarch@...ts.linux.dev, sparclinux@...r.kernel.org, x86@...nel.org,
        Hendrik Brueckner <brueckner@...ux.ibm.com>
Subject: Re: [PATCH 07/15] s390/crc32: expose CRC32 functions through lib

On Sun, Oct 20, 2024 at 05:29:27PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> Move the s390 CRC32 assembly code into the lib directory and wire it up
> to the library interface.  This allows it to be used without going
> through the crypto API.  It remains usable via the crypto API too via
> the shash algorithms that use the library interface.  Thus all the
> arch-specific "shash" code becomes unnecessary and is removed.
> 
> Note: to see the diff from arch/s390/crypto/crc32-vx.c to
> arch/s390/lib/crc32-glue.c, view this commit with 'git show -M10'.
> 
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> ---
>  arch/s390/Kconfig                      |   1 +
>  arch/s390/configs/debug_defconfig      |   1 -
>  arch/s390/configs/defconfig            |   1 -
>  arch/s390/crypto/Kconfig               |  12 -
>  arch/s390/crypto/Makefile              |   2 -
>  arch/s390/crypto/crc32-vx.c            | 306 -------------------------
>  arch/s390/lib/Makefile                 |   3 +
>  arch/s390/lib/crc32-glue.c             |  82 +++++++
>  arch/s390/{crypto => lib}/crc32-vx.h   |   0
>  arch/s390/{crypto => lib}/crc32be-vx.c |   0
>  arch/s390/{crypto => lib}/crc32le-vx.c |   0
>  11 files changed, 86 insertions(+), 322 deletions(-)
>  delete mode 100644 arch/s390/crypto/crc32-vx.c
>  create mode 100644 arch/s390/lib/crc32-glue.c
>  rename arch/s390/{crypto => lib}/crc32-vx.h (100%)
>  rename arch/s390/{crypto => lib}/crc32be-vx.c (100%)
>  rename arch/s390/{crypto => lib}/crc32le-vx.c (100%)

...

> -static int __init crc_vx_mod_init(void)
> -{
> -	return crypto_register_shashes(crc32_vx_algs,
> -				       ARRAY_SIZE(crc32_vx_algs));
> -}
> -
> -static void __exit crc_vx_mod_exit(void)
> -{
> -	crypto_unregister_shashes(crc32_vx_algs, ARRAY_SIZE(crc32_vx_algs));
> -}
> -
> -module_cpu_feature_match(S390_CPU_FEATURE_VXRS, crc_vx_mod_init);

What makes sure that all of the code is available automatically if the
CPU supports the instructions like before? I can see that all CRC32
related config options support also module build options.

Before this patch, this module and hence the fast crc32 variants were
loaded automatically when required CPU features were present.
Right now I don't how this is happening with this series.

> -MODULE_ALIAS_CRYPTO("crc32");
> -MODULE_ALIAS_CRYPTO("crc32-vx");
> -MODULE_ALIAS_CRYPTO("crc32c");
> -MODULE_ALIAS_CRYPTO("crc32c-vx");

...

> +static int __init crc32_s390_init(void)
> +{
> +	if (cpu_have_feature(S390_CPU_FEATURE_VXRS))
> +		static_branch_enable(&have_vxrs);
> +	return 0;
> +}
> +arch_initcall(crc32_s390_init);

I guess this should be changed to:

module_cpu_feature_match(S390_CPU_FEATURE_VXRS, ...);

Which would make at least the library functions available if cpu
features are present. But this looks only like a partial solution of
the above described problem.

But maybe I'm missing something.