[PATCH v2 1/4] arm64: Document requirements for fine grained traps at boot

[Marc Zyngier]

On Thu, 01 Apr 2021 19:09:39 +0100,
Mark Brown <broonie at kernel.org> wrote:
> 
> The arm64 FEAT_FGT extension introduces a set of traps to EL2 for accesses
> to small sets of registers and instructions from EL1 and EL0, access to
> which is controlled by EL3.  Require access to it so that it is
> available to us in future and so that we can ensure these traps are
> disabled during boot.
> 
> Signed-off-by: Mark Brown <broonie at kernel.org>
> ---
>  Documentation/arm64/booting.rst | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/Documentation/arm64/booting.rst b/Documentation/arm64/booting.rst
> index 7552dbc1cc54..92ec0bea1af5 100644
> --- a/Documentation/arm64/booting.rst
> +++ b/Documentation/arm64/booting.rst
> @@ -270,6 +270,12 @@ Before jumping into the kernel, the following conditions must be met:
>        having 0b1 set for the corresponding bit for each of the auxiliary
>        counters present.
>  
> +  For CPUs with the Fine Grained Traps (FEAT_FGT) extension present:
> +
> +  - If EL3 is present and the kernel is entered at EL2:
> +
> +    - SCR_EL3.FGTEn (bit 27) must be initialised to 0b1.
> +
>  The requirements described above for CPU mode, caches, MMUs, architected
>  timers, coherency and system registers apply to all CPUs.  All CPUs must
>  enter the kernel in the same exception level.

Acked-by: Marc Zyngier <maz at kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.