Re: [PATCH v2 4/4] xen/arm: mpu: Implement a dummy enable_secondary_cpu_mm

[Julien Grall <julien@xxxxxxx>]

Hi,

On 18/09/2024 19:51, Ayan Kumar Halder wrote:
> Secondary cpus initialization is not yet supported. Thus, we print an
> appropriate message and put the secondary cpus in WFE state.
>
> Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
> ---
> Changes from :-
>
> v1 - 1. NR_CPUS is defined as 1 for MPU
>
> 2. Added a message in enable_secondary_cpu_mm()
>
>   xen/arch/Kconfig              |  1 +
>   xen/arch/arm/arm64/mpu/head.S | 10 ++++++++++
>   2 files changed, 11 insertions(+)
>
> diff --git a/xen/arch/Kconfig b/xen/arch/Kconfig
> index 308ce129a8..8640b7ec8b 100644
> --- a/xen/arch/Kconfig
> +++ b/xen/arch/Kconfig
> @@ -11,6 +11,7 @@ config NR_CPUS
>         default "8" if ARM && RCAR3
>         default "4" if ARM && QEMU
>         default "4" if ARM && MPSOC
> +       default "1" if ARM && MPU
>         default "128" if ARM
>         help
>           Controls the build-time size of various arrays and bitmaps
> diff --git a/xen/arch/arm/arm64/mpu/head.S b/xen/arch/arm/arm64/mpu/head.S
> index ef55c8765c..3dfbbf8879 100644
> --- a/xen/arch/arm/arm64/mpu/head.S
> +++ b/xen/arch/arm/arm64/mpu/head.S
> @@ -168,6 +168,16 @@ FUNC(enable_boot_cpu_mm)
>       b   1b
>   END(enable_boot_cpu_mm)
>   
> +/*
> + * Secondary cpu has not yet been supported on MPU systems. We will block the
> + * secondary cpu bringup at this stage.
Given that NR_CPUS is 1, this should not be reachable. How about the 
following comment:
"We don't yet support secondary CPUs bring-up. Implement a dummy helper 
to please the common code."
> + */
> +ENTRY(enable_secondary_cpu_mm)
> +1:  PRINT("- SMP not enabled yet -\r\n")
You want the print to be outside of the loop. Otherwise, it will spam 
the console in the unlikely case the code is reached.
> +    wfe
> +    b 1b
> +ENDPROC(enable_secondary_cpu_mm)
> +
>   /*
>    * Local variables:
>    * mode: ASM
Cheers,

--
Julien Grall