[PATCH 04/13] arm64: Add new hcall HVC_CALL_FUNC

[Will Deacon]

On Tue, Sep 09, 2014 at 11:49:04PM +0100, Geoff Levand wrote:
> Add the new hcall HVC_CALL_FUNC that allows execution of a function at EL2.
> During CPU reset the CPU must be brought to the exception level it had on
> entry to the kernel.  The HVC_CALL_FUNC hcall will provide the mechanism
> needed for this exception level switch.
> 
> Signed-off-by: Geoff Levand <geoff at infradead.org>
> ---
>  arch/arm64/include/asm/virt.h | 11 +++++++++++
>  arch/arm64/kernel/hyp-stub.S  | 10 ++++++++++
>  2 files changed, 21 insertions(+)

[...]

> diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
> index 9ab5f70..a21cf51 100644
> --- a/arch/arm64/kernel/hyp-stub.S
> +++ b/arch/arm64/kernel/hyp-stub.S
> @@ -75,7 +75,17 @@ el1_sync:
>  1:	cmp	x10, #HVC_SET_VECTORS
>  	b.ne	1f
>  	msr	vbar_el2, x0
> +	b	2f
>  
> +1:	cmp	x10, #HVC_CALL_FUNC
> +	b.ne    1f
> +	mov	x29, lr
> +	mov	lr, x0
> +	mov	x0, x1
> +	mov	x1, x2
> +	mov	x2, x3
> +	blr	lr
> +	mov	lr, x29

Why are you clobbering x29?

Will