[PATCH 3/8] arm64: Add new hcall HVC_CALL_FUNC

[Catalin Marinas]

On Sat, Jan 17, 2015 at 12:23:34AM +0000, Geoff Levand wrote:
> diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> index 99c319c..4f23a48 100644
> --- a/arch/arm64/include/asm/virt.h
> +++ b/arch/arm64/include/asm/virt.h
> @@ -41,6 +41,19 @@
>  
>  #define HVC_CALL_HYP 3
>  
> +/*
> + * HVC_CALL_FUNC - Execute a function at EL2.
> + *
> + * @x0: Physical address of the function to be executed.
> + * @x1: Passed as the first argument to the function.
> + * @x2: Passed as the second argument to the function.
> + * @x3: Passed as the third argument to the function.
> + *
> + * The called function must preserve the contents of register x18.

Can you pick a register that's normally callee saved?

> + */
> +
> +#define HVC_CALL_FUNC 4
> +
>  #ifndef __ASSEMBLY__
>  
>  /*
> diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
> index e3db3fd..b5d36e7 100644
> --- a/arch/arm64/kernel/hyp-stub.S
> +++ b/arch/arm64/kernel/hyp-stub.S
> @@ -66,9 +66,20 @@ el1_sync:
>  	mrs	x0, vbar_el2
>  	b	2f
>  
> -1:	cmp	x18, #HVC_SET_VECTORS
> -	b.ne	2f
> -	msr	vbar_el2, x0
> +1:	cmp     x18, #HVC_SET_VECTORS

This line doesn't seem to have any change, apart from some whitespace.
Or did you want to drop the label?

> +	b.ne    1f
> +	msr     vbar_el2, x0
> +	b       2f
> +
> +1:	cmp     x18, #HVC_CALL_FUNC
> +	b.ne    2f
> +	mov     x18, lr
> +	mov     lr, x0
> +	mov     x0, x1
> +	mov     x1, x2
> +	mov     x2, x3
> +	blr     lr
> +	mov     lr, x18
>  
>  2:	eret
>  ENDPROC(el1_sync)

What is the calling convention for this HVC? You mentioned x18 above but
what about other registers that the called function may corrupt (x18 is
a temporary register, so it's not expected to be callee saved).

-- 
Catalin