[PATCH V2 04/13] arm64: Add new hcall HVC_CALL_FUNC

[geoff@infradead.org (Geoff Levand)]

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 | 13 +++++++++++++
 arch/arm64/kernel/hyp-stub.S  | 10 ++++++++++
 2 files changed, 23 insertions(+)

diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
index 894fe53..cc4250c 100644
--- a/arch/arm64/include/asm/virt.h
+++ b/arch/arm64/include/asm/virt.h
@@ -41,6 +41,19 @@
 
 #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 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.
+ */
+
+#define HVC_CALL_FUNC 4
+
 #ifndef __ASSEMBLY__
 
 /*
diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
index 9ab5f70..27d786d 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	x18, lr
+	mov	lr, x0
+	mov	x0, x1
+	mov	x1, x2
+	mov	x2, x3
+	blr	lr
+	mov	lr, x18
 1:
 2:	eret
 ENDPROC(el1_sync)
-- 
1.9.1