Re: [PATCH] lib/crc: make the CPU feature static keys __ro_after_init

[Eric Biggers <ebiggers@kernel.org>]

On Thu, Apr 17, 2025 at 02:53:18PM +0200, Heiko Carstens wrote:
> On Sun, Apr 13, 2025 at 08:43:50AM -0700, Eric Biggers wrote:
> > From: Eric Biggers <ebiggers@google.com>
> > 
> > All of the CRC library's CPU feature static_keys are initialized by
> > initcalls and never change afterwards, so there's no need for them to be
> > in the regular .data section.  Put them in .data..ro_after_init instead.
> > 
> > Signed-off-by: Eric Biggers <ebiggers@google.com>
> > ---
> > 
> > I'm planning to take this via the crc tree.
> > 
> >  arch/arm/lib/crc-t10dif-glue.c       | 4 ++--
> >  arch/arm/lib/crc32-glue.c            | 4 ++--
> >  arch/arm64/lib/crc-t10dif-glue.c     | 4 ++--
> >  arch/loongarch/lib/crc32-loongarch.c | 2 +-
> >  arch/mips/lib/crc32-mips.c           | 2 +-
> >  arch/powerpc/lib/crc-t10dif-glue.c   | 2 +-
> >  arch/powerpc/lib/crc32-glue.c        | 2 +-
> >  arch/s390/lib/crc32-glue.c           | 2 +-
> 
> 
> Acked-by: Heiko Carstens <hca@linux.ibm.com> # s390
> 
> I just realized that we can get rid of the static key in the s390
> piece and end up with slightly better code. Could you add the patch
> below to your tree, please? If this would go via the s390 tree this
> would result in a merge conflict, which is unnecessary.
> 
> From 6c4c0ca6fe87e43acf6192f1afc0a6346db994f4 Mon Sep 17 00:00:00 2001
> From: Heiko Carstens <hca@linux.ibm.com>
> Date: Thu, 17 Apr 2025 14:30:56 +0200
> Subject: [PATCH] s390/crc32: Remove have_vxrs static key
> 
> Replace the have_vxrs static key with a cpu_has_vx() call.  cpu_has_vx()
> resolves into a compile time constant (true) if the kernel is compiled for
> z13 or newer. Otherwise it generates an unconditional one instruction
> branch, which is patched based on CPU alternatives.
> 
> In any case the generated code is at least as good as before and avoids
> static key handling.
> 
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
> ---
>  arch/s390/lib/crc32-glue.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)

Thanks!  Applied to
https://web.git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/log/?h=crc-next

- Eric