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

Mark Rutland
2014-09-15T18:11:01Z

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@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/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> index 894fe53..b217fbc 100644
> --- a/arch/arm64/include/asm/virt.h
> +++ b/arch/arm64/include/asm/virt.h
> @@ -41,6 +41,17 @@
>
> #define HVC_KVM_CALL_HYP 3
>
> +/*
> + * HVC_CALL_FUNC - Execute a function at EL2.
> + *
> + * @x0: Physical address of the funtion to be executed.
> + * @x1: Passed as the first argument to @fn.
> + * @x2: Passed as the second argument to @fn.
> + * @x3: Passed as the third argument to @fn.
> + */
> +
> +#define HVC_CALL_FUNC 4
> +

Can't we use the HVC_KVM_CALL_HYP for this as well? I thought we already
added the code to the stub to do that in the last patch.

Is there a difference between the two that I'm missing?

> #ifndef __ASSEMBLY__
>
> /*
> 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

What's the contract for functions we call through the stub?

If they can use all the caller-saved registers, then we need to stach
the original LR before issuing the HVC. Otherwise we can stash it in
x18 at EL2.

Thanks,
Mark.