ARM: HYP/non-sec: migrate stack

The current code that switches into HYP mode doesn't bother to set
up a stack for HYP mode.  This doesn't work for EFI applications
as they expect a usable stack.  Fix this by migrating the stack
pointer from SP_svc to SP_hyp while in Monitor mode.
This restores the stack pointer when we drop into HYP mode.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/arm/cpu/armv7/nonsec_virt.S

@@ -80,6 +80,8 @@ _secure_monitor:
 #ifdef CONFIG_ARMV7_VIRT
 	orreq	r5, r5, #0x100			@ allow HVC instruction
 	moveq	r6, #HYP_MODE			@ Enter the kernel as HYP
+	mrseq	r3, sp_svc
+	msreq	sp_hyp, r3			@ migrate SP
 #endif
 
 	mcr	p15, 0, r5, c1, c1, 0		@ write SCR (with NS bit set)