# Re: \[PATCH 5/5\] arm64: Document the requirement for SCR\_EL3.HCE

- From: Catalin Marinas \<catalin.marinas@arm.com\>
- Date: 2021-08-24 10:49:08 
- List: linux-arm-kernel
- Page: https://ratatoskr.run/linux-arm-kernel/2021/08/1486873
- Thread: https://ratatoskr.run/linux-arm-kernel/2021/08/1476373/t.md

```text
On Thu, Aug 12, 2021 at 08:02:13PM +0100, Marc Zyngier wrote:
> It is amazing that we never documented this absolutely basic
> requirement: if you boot the kernel at EL2, you'd better
> enable the HVC instruction from EL3.
> 
> Really, just do it.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  Documentation/arm64/booting.rst | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/Documentation/arm64/booting.rst b/Documentation/arm64/booting.rst
> index a9192e7a231b..6c729d0c4bc2 100644
> --- a/Documentation/arm64/booting.rst
> +++ b/Documentation/arm64/booting.rst
> @@ -212,6 +212,11 @@ Before jumping into the kernel, the following conditions must be met:
>    - The value of SCR_EL3.FIQ must be the same as the one present at boot
>      time whenever the kernel is executing.
>  
> +  For all systems:
> +  - If EL3 is present and the kernel is entered at EL2:
> +
> +    - SCR_EL3.HCE (bit 8) must be initialised to 0b1.
> +
>    For systems with a GICv3 interrupt controller to be used in v3 mode:
>    - If EL3 is present:

I'll queue this patch only for now.

A nitpick, I think we should move "For all systems" and "If EL3 is
present..." above the lines describing the SCR_EL3.FIQ requirement (I
can make the change locally).

-- 
Catalin

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