Re: [Xen-devel] [PATCH 1/2] xen: arm64: doc: Add the requirement that SCR_EL3.HCE is enabled

[Julien Grall <julien.grall@xxxxxxx>]

(CC REST maintainers)

Hello Dirk,

Please CC the relevant maintainers for this patch. You can use 
scripts/get_maintainers.pl for this purpose.
On 19/04/16 06:59, Dirk Behme wrote:
> On ARM64 Linux the HVC instruction is used to trap into Xen. As this
> can be set only at EL3, i.e. outside from Xen, document this boot
> requirement.
>
> Signed-off-by: Dirk Behme <dirk.behme@xxxxxxxxxxxx>
> ---
>   docs/misc/arm/booting.txt | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/docs/misc/arm/booting.txt b/docs/misc/arm/booting.txt
> index 9802e5e..ffc9029 100644
> --- a/docs/misc/arm/booting.txt
> +++ b/docs/misc/arm/booting.txt
> @@ -23,6 +23,10 @@ The exceptions to this on 32-bit ARM are as follows:
>
>   There are no exception on 64-bit ARM.
>
> +On ARM64 Linux it has to be ensured that the Secure Configuration
> +Register has the HVC instructions enabled at EL1 and above
> +(SCR_EL3.HCE == 1).
The requirement is the same for ARM32 (SCR.HCE == 1).

I would create a specific section in this documentation to list what the 
firmware should do in EL3 before starting Xen.
In addition to this patch, I would add a check in Xen to make sure the 
Hyp calls have been enabled by the firmware.
Regards,

> +
>   [1] linux/Documentation/arm/Booting
>   Latest version: 
> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm/Booting
--
Julien Grall

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