[PATCH] arm64: Document boot requirements for FEAT_SME_FA64

[Will Deacon]

On Mon, Oct 25, 2021 at 01:48:22PM +0100, Mark Brown wrote:
> The EAC1 release of the SME specification adds the FA64 feature which
> requires enablement at higher ELs before lower ELs can use it. Document
> what we require from higher ELs in our boot requirements.
> 
> Signed-off-by: Mark Brown <broonie at kernel.org>
> ---
>  Documentation/arm64/booting.rst | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/Documentation/arm64/booting.rst b/Documentation/arm64/booting.rst
> index 3f9d86557c5e..0047d3b42d5c 100644
> --- a/Documentation/arm64/booting.rst
> +++ b/Documentation/arm64/booting.rst
> @@ -340,6 +340,16 @@ Before jumping into the kernel, the following conditions must be met:
>      - SMCR_EL2.LEN must be initialised to the same value for all CPUs the
>        kernel will execute on.
>  
> +  For CPUs with the Scalable Matrix Extension FA64 feature (FEAT_SME_FA64)
> +
> +  - If EL3 is present:
> +
> +    - SMCR_EL3.FA64 (bit 31) must be initialised to to 0b1.
> +
> + - If the kernel is entered at EL1 and EL2 is present:
> +
> +    - SMCR_EL2.FA64 (bit 31) must be initialised to to 0b1.

"to to"

With the second bullet, does that mean KVM is in violation of our own
documentation?

Will