arm64: hyp-stub: Define a return value for failed stub calls

Define a standard return value to be returned when a hyp stub
call fails, and make KVM use it for ARM_EXCEPTION_HYP_GONE
(instead of using a KVM-specific value).
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>

arch/arm64/include/asm/kvm_asm.h

@@ -28,7 +28,7 @@
 #define ARM_EXCEPTION_EL1_SERROR  1
 #define ARM_EXCEPTION_TRAP	  2
 /* The hyp-stub will return this for any kvm_call_hyp() call */
-#define ARM_EXCEPTION_HYP_GONE	  3
+#define ARM_EXCEPTION_HYP_GONE	  HVC_STUB_ERR
 
 #define KVM_ARM64_DEBUG_DIRTY_SHIFT	0
 #define KVM_ARM64_DEBUG_DIRTY		(1 << KVM_ARM64_DEBUG_DIRTY_SHIFT)

arch/arm64/include/asm/virt.h

@@ -39,6 +39,9 @@
  */
 #define HVC_SOFT_RESTART 2
 
+/* Error returned when an invalid stub number is passed into x0 */
+#define HVC_STUB_ERR	0xbadca11
+
 #define BOOT_CPU_MODE_EL1	(0xe11)
 #define BOOT_CPU_MODE_EL2	(0xe12)
 

arch/arm64/kernel/hyp-stub.S

@@ -74,7 +74,7 @@ el1_sync:
 	br	x4				// no return
 
 	/* Someone called kvm_call_hyp() against the hyp-stub... */
-3:	mov	x0, #ARM_EXCEPTION_HYP_GONE
+3:	ldr	x0, =HVC_STUB_ERR
 
 9:	eret
 ENDPROC(el1_sync)