Re: [PATCH] arm64/fpsimd: signal: Forbid non-streaming SVE payload on SME-only systems

[Mark Rutland <mark.rutland@arm.com>]

On Thu, Oct 01, 2026 at 03:25:03PM +0100, Mark Brown wrote:
> On Thu, Oct 01, 2026 at 02:08:36PM +0100, Mark Rutland wrote:
> > @@ -443,19 +444,33 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user)
> 
> >  	} else {
> >  		/*
> > -		 * A SME only system use SVE for streaming mode so can
> > -		 * have a SVE formatted context with a zero VL and no
> > -		 * payload data.
> > +		 * Non-streaming SVE state may be preserved without an SVE
> > +		 * payload, in which case all state is saved in the FPSIMD
> > +		 * context.
> > +		 *
> > +		 * On SME-only systems, non-streaming (FPSIMD-only) state is
> > +		 * always preserved without an SVE payload, and with VL==0. On
> > +		 * such systems, only accept non-streaming state without an SVE
> > +		 * payload.
> >  		 */
> > -		if (!system_supports_sve() && !system_supports_sme())
> > +		if (!system_supports_sve() && !fpsimd_only)
> >  			return -EINVAL;
> 
> This means that this function will now accept a FPSIMD only SVE context
> on systems with neither SVE nor SME, but that check was redundant since
> we already reject anything with SVE magic in parse_user_sigframe() on
> such systems and should never get here anyway.

Yes. The commit message explained that:

  As parse_user_sigframe() rejects SVE signal frames when neither SVE
  nor SME are supported, it isn't necessary for
  restore_sve_fpsimd_context() to handle the case where neither are
  supported.

> Reviewed-by: Mark Brown <broonie@kernel.org>

Thanks.

Mark.