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

[Geoff Levand]

Hi Will,

On Wed, 2014-09-10 at 18:07 +0100, Will Deacon wrote:
> 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?

I can change this to x28, unless you can recommend another?

-Geoff