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

Will Deacon
2014-09-10T17:07:40Z

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/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