[PATCH 2/2] arm64: document that pending SErrors are not allowed at kernel entry

[mark.rutland@arm.com (Mark Rutland)]

On Fri, Jul 01, 2016 at 05:01:31PM +0200, Ard Biesheuvel wrote:
> Our current strategy to deal with pending SErrors at boot is to panic.
> So let's mention in our boot protocol documentation that no SErrors
> should be pending when handing over to the kernel.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  Documentation/arm64/booting.txt | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/arm64/booting.txt b/Documentation/arm64/booting.txt
> index 8d0df62c3fe0..75dcfead1a0c 100644
> --- a/Documentation/arm64/booting.txt
> +++ b/Documentation/arm64/booting.txt
> @@ -154,8 +154,9 @@ Before jumping into the kernel, the following conditions must be met:
>    x3 = 0 (reserved for future use)
>  
>  - CPU mode
> -  All forms of interrupts must be masked in PSTATE.DAIF (Debug, SError,
> -  IRQ and FIQ).
> +  All forms of exceptions must be masked in PSTATE.DAIF (Debug, SError,
> +  IRQ and FIQ), and any pending SError exceptions must be taken by the
> +  boot loader or firmware before handing over to the kernel.

That can be read to mean that a loader should silently swallow SError,
which isn't quite what we want (that no SError ever occurs). I don't
have a better wording to suggest, unfortunately. :/

As with patch 1, I'm not sure what this means for CPER and friends.

Thanks,
Mark.

>    The CPU must be in either EL2 (RECOMMENDED in order to have access to
>    the virtualisation extensions) or non-secure EL1.
>  
> -- 
> 2.7.4
>