Re: [PATCH v12 04/29] arm64/sve: Factor virtualizable VL discovery out of SVE specific code

[Fuad Tabba <fuad.tabba@linux.dev>]

Hi Mark,

On Thu, 9 Jul 2026 at 19:40, Mark Brown <broonie@kernel.org> wrote:
>
> In preparation for reuising it for SME pull the code for discovering the
> maximum virtualizable vector length out of sve_setup() into a separate
> function.
>
> Signed-off-by: Mark Brown <broonie@kernel.org>
> ---
>  arch/arm64/kernel/fpsimd.c | 41 ++++++++++++++++++++++++-----------------
>  1 file changed, 24 insertions(+), 17 deletions(-)
>
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index dc1ad10e39a2..5c156e2a47ea 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -1114,6 +1114,29 @@ int vec_verify_vq_map(enum vec_type type)
>         return 0;
>  }
>
> +static int vec_virtualisable_vl(struct vl_info *info)
> +{
> +       DECLARE_BITMAP(partial_only_map, SVE_VQ_MAX);
> +       unsigned long b_min_partial, b_max_virt;
> +
> +       bitmap_andnot(partial_only_map, info->vq_partial_map, info->vq_map,
> +                     SVE_VQ_MAX);
> +       b_min_partial = find_last_bit(partial_only_map, SVE_VQ_MAX);
> +
> +       /* All implemented VLs are virtualisable */
> +       if (b_min_partial >= SVE_VQ_MAX)
> +               return info->max_vl;
> +
> +       b_max_virt = find_next_bit(info->vq_map, SVE_VQ_MAX, b_min_partial);
> +
> +       /* No implemented VLs are virtualisable */
> +       if (b_max_virt >= SVE_VQ_MAX)
> +               return 0;

nit: this is a reimplementation rather than a straight move, the
no-virtualisable case returns 0 (and drops the WARN_ON) where
sve_setup() returned SVE_VQ_MIN. No change for SVE (that case isn't
architecturally possible), and 0 is correct for the SME case this
helper now also serves. Might be worth a word in the changelog, since
"pull ... into a separate function" reads as pure code motion.

Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>

Cheers,
/fuad



> +
> +       /* At least one virtualisable VL exists */
> +       return sve_vl_from_vq(__bit_to_vq(b_max_virt));
> +}
> +
>  void cpu_enable_sve(const struct arm64_cpu_capabilities *__always_unused p)
>  {
>         write_sysreg(read_sysreg(CPACR_EL1) | CPACR_EL1_ZEN_EL1EN, CPACR_EL1);
> @@ -1125,8 +1148,6 @@ void cpu_enable_sve(const struct arm64_cpu_capabilities *__always_unused p)
>  void __init sve_setup(void)
>  {
>         struct vl_info *info = &vl_info[ARM64_VEC_SVE];
> -       DECLARE_BITMAP(tmp_map, SVE_VQ_MAX);
> -       unsigned long b;
>         int max_bit;
>
>         if (!system_supports_sve())
> @@ -1149,21 +1170,7 @@ void __init sve_setup(void)
>          */
>         set_sve_default_vl(find_supported_vector_length(ARM64_VEC_SVE, 64));
>
> -       bitmap_andnot(tmp_map, info->vq_partial_map, info->vq_map,
> -                     SVE_VQ_MAX);
> -
> -       b = find_last_bit(tmp_map, SVE_VQ_MAX);
> -       if (b >= SVE_VQ_MAX)
> -               /* No non-virtualisable VLs found */
> -               info->max_virtualisable_vl = SVE_VQ_MAX;
> -       else if (WARN_ON(b == SVE_VQ_MAX - 1))
> -               /* No virtualisable VLs?  This is architecturally forbidden. */
> -               info->max_virtualisable_vl = SVE_VQ_MIN;
> -       else /* b + 1 < SVE_VQ_MAX */
> -               info->max_virtualisable_vl = sve_vl_from_vq(__bit_to_vq(b + 1));
> -
> -       if (info->max_virtualisable_vl > info->max_vl)
> -               info->max_virtualisable_vl = info->max_vl;
> +       info->max_virtualisable_vl = vec_virtualisable_vl(info);
>
>         pr_info("%s: maximum available vector length %u bytes per vector\n",
>                 info->name, info->max_vl);
>
> --
> 2.47.3
>