[PATCH] crypto: arm64/sha256 - fix build when CONFIG_PREEMPT_VOLUNTARY=y

[Ard Biesheuvel]

On Wed, 7 May 2025 at 19:09, Eric Biggers <ebiggers at kernel.org> wrote:
>
> From: Eric Biggers <ebiggers at google.com>
>
> Fix the build of sha256-ce.S when CONFIG_PREEMPT_VOLUNTARY=y by passing
> the correct label to the cond_yield macro.  Also adjust the code to
> execute only one branch instruction when CONFIG_PREEMPT_VOLUNTARY=n.
>
> Fixes: 6e36be511d28 ("crypto: arm64/sha256 - implement library instead of shash")
> Reported-by: kernel test robot <lkp at intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202505071811.yYpLUbav-lkp@intel.com/
> Signed-off-by: Eric Biggers <ebiggers at google.com>
> ---
>  arch/arm64/lib/crypto/sha256-ce.S | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/lib/crypto/sha256-ce.S b/arch/arm64/lib/crypto/sha256-ce.S
> index a8461d6dad634..f3e21c6d87d2e 100644
> --- a/arch/arm64/lib/crypto/sha256-ce.S
> +++ b/arch/arm64/lib/crypto/sha256-ce.S
> @@ -121,14 +121,15 @@ CPU_LE(   rev32           v19.16b, v19.16b        )
>
>         /* update state */
>         add             dgav.4s, dgav.4s, dg0v.4s
>         add             dgbv.4s, dgbv.4s, dg1v.4s
>
> +       /* return early if voluntary preemption is needed */
> +       cond_yield      1f, x5, x6
> +

This will yield needlessly when the condition hits during the final iteration.

>         /* handled all input blocks? */
> -       cbz             x2, 1f
> -       cond_yield      3f, x5, x6
> -       b               0b
> +       cbnz            x2, 0b
>
>         /* store new state */
>  1:     st1             {dgav.4s, dgbv.4s}, [x0]
>         mov             x0, x2
>         ret
>
> base-commit: 20e9579f11b6cbdf0556d9cd85a0aa7653caf341
> --
> 2.49.0
>