Re: [PATCH v2] arm64/signal: Clean up SVE/SME feature checking inconsistency

[Will Deacon <will@kernel.org>]

On Fri, Jun 24, 2022 at 02:44:14PM +0100, Mark Brown wrote:
> Currently when restoring signal state we check to see if SVE is supported
> in restore_sigframe() but check to see if SVE is supported inside
> restore_sve_fpsimd_context(). This makes no real difference since SVE is
> always supported in systems with SME but looks a bit untidy and makes
> things slightly harder to follow, move the SVE check next to the SME one
> in restore_sve_fpsimd_context().
> 
> Signed-off-by: Mark Brown <broonie@kernel.org>
> ---
> 
> v2:
>  - Add a stub restore_sve_fpsimd_context() to hopefully fix an
>    allnoconfig issue, I can't reproduce locally.
> 
>  arch/arm64/kernel/signal.c | 19 +++++++++++--------
>  1 file changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
> index b0980fbb6bc7..6b6a79806e82 100644
> --- a/arch/arm64/kernel/signal.c
> +++ b/arch/arm64/kernel/signal.c
> @@ -280,6 +280,9 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user)
>  
>  		vl = task_get_sme_vl(current);
>  	} else {
> +		if (!system_supports_sve())
> +			return -EINVAL;
> +
>  		vl = task_get_sve_vl(current);
>  	}
>  
> @@ -342,9 +345,13 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user)
>  
>  #else /* ! CONFIG_ARM64_SVE */
>  
> -/* Turn any non-optimised out attempts to use these into a link error: */
> +static int restore_sve_fpsimd_context(struct user_ctxs *user)
> +{
> +	return 0;
> +}

Given that this should never be called, should we return an error instead
of 0 (or possibly even WARN/BUG)?

Will

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