Re: [Xen-devel] [PATCH 07/17] xen/arm64: head: Rework and document check_cpu_mode()

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 10 Jun 2019, Julien Grall wrote:
> A branch in the success case can be avoided by inverting the branch
> condition. At the same time, remove a pointless comment as Xen can only
> run at EL2.
> 
> Lastly, document the behavior and the main registers usage within the
> function.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

> ---
>  xen/arch/arm/arm64/head.S | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
> index ccd8a1b0a8..87fcd3be6c 100644
> --- a/xen/arch/arm/arm64/head.S
> +++ b/xen/arch/arm/arm64/head.S
> @@ -350,6 +350,13 @@ secondary_switched:
>          b     launch
>  ENDPROC(init_secondary)
>  
> +/*
> + * Check if the CPU has been booted in Hypervisor mode.
> + * This function will never return when the CPU is booted in another mode
> + * than Hypervisor mode.
> + *
> + * Clobbers x0 - x5
> + */
>  check_cpu_mode:
>          PRINT("- Current EL ")
>          mrs   x5, CurrentEL
> @@ -359,15 +366,13 @@ check_cpu_mode:
>          /* Are we in EL2 */
>          cmp   x5, #PSR_MODE_EL2t
>          ccmp  x5, #PSR_MODE_EL2h, #0x4, ne
> -        b.eq  el2 /* Yes */
> -
> +        b.ne  1f /* No */
> +        ret
> +1:
>          /* OK, we're boned. */
>          PRINT("- Xen must be entered in NS EL2 mode -\r\n")
>          PRINT("- Please update the bootloader -\r\n")
>          b fail
> -
> -el2:    PRINT("- Xen starting at EL2 -\r\n")
> -        ret
>  ENDPROC(check_cpu_mode)
>  
>  zero_bss:
> -- 
> 2.11.0
> 

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