Re: [Xen-devel] [PATCH v3 14/28] xen/arm32: head: Rework and document check_cpu_mode()

[Stefano Stabellini <sstabellini@kernel.org>]

On Mon, 12 Aug 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 Hypervisor Mode.
> 
> Lastly, document the behavior and the main registers usage within the
> function.
> 
> Signed-off-by: Julien Grall <julien.grall@arm.com>

Already provided by reviewed-by last time

> ---
>     Changes in v2:
>         - Patch added
> ---
>  xen/arch/arm/arm32/head.S | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
> index 4285f76463..c7b4fe4cd4 100644
> --- a/xen/arch/arm/arm32/head.S
> +++ b/xen/arch/arm/arm32/head.S
> @@ -206,6 +206,16 @@ secondary_switched:
>          b     launch
>  ENDPROC(init_secondary)
>  
> +/*
> + * Check if the CPU supports virtualization extensions and has been booted
> + * in Hypervisor mode.
> + *
> + * This function will never return when the CPU doesn't support
> + * virtualization extensions or is booted in another mode than
> + * Hypervisor mode.
> + *
> + * Clobbers r0 - r3
> + */
>  check_cpu_mode:
>          /* Check that this CPU has Hyp mode */
>          mrc   CP32(r0, ID_PFR1)
> @@ -220,15 +230,12 @@ check_cpu_mode:
>          mrs   r0, cpsr
>          and   r0, r0, #0x1f          /* Mode is in the low 5 bits of CPSR */
>          teq   r0, #0x1a              /* Hyp Mode? */
> -        beq   hyp
> +        moveq pc, lr                 /* Yes, return */
>  
>          /* OK, we're boned. */
>          PRINT("- Xen must be entered in NS Hyp mode -\r\n")
>          PRINT("- Please update the bootloader -\r\n")
>          b     fail
> -
> -hyp:    PRINT("- Xen starting in Hyp mode -\r\n")
> -        mov   pc, lr
>  ENDPROC(check_cpu_mode)
>  
>  zero_bss:
> -- 
> 2.11.0
> 

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