KVM: PPC: Book3S HV: Prepare for host using hypervisor doorbells

POWER8 has support for hypervisor doorbell interrupts.  Though the
kernel doesn't use them for IPIs on the powernv platform yet, it
probably will in future, so this makes KVM cope gracefully if a
hypervisor doorbell interrupt arrives while in a guest.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/include/asm/kvm_asm.h

@@ -96,6 +96,7 @@
 #define BOOK3S_INTERRUPT_H_DATA_STORAGE	0xe00
 #define BOOK3S_INTERRUPT_H_INST_STORAGE	0xe20
 #define BOOK3S_INTERRUPT_H_EMUL_ASSIST	0xe40
+#define BOOK3S_INTERRUPT_H_DOORBELL	0xe80
 #define BOOK3S_INTERRUPT_PERFMON	0xf00
 #define BOOK3S_INTERRUPT_ALTIVEC	0xf20
 #define BOOK3S_INTERRUPT_VSX		0xf40

arch/powerpc/kvm/book3s_hv.c

@@ -651,6 +651,7 @@ static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
 		r = RESUME_GUEST;
 		break;
 	case BOOK3S_INTERRUPT_EXTERNAL:
+	case BOOK3S_INTERRUPT_H_DOORBELL:
 		vcpu->stat.ext_intr_exits++;
 		r = RESUME_GUEST;
 		break;

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -1997,10 +1997,17 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_ARCH_207S)
 BEGIN_FTR_SECTION
 	cmpwi	r6, 5			/* privileged doorbell? */
 	beq	0f
+	cmpwi	r6, 3			/* hypervisor doorbell? */
+	beq	3f
 END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 	li	r3, 1			/* anything else, return 1 */
 0:	blr
 
+	/* hypervisor doorbell */
+3:	li	r12, BOOK3S_INTERRUPT_H_DOORBELL
+	li	r3, 1
+	blr
+
 /*
  * Determine what sort of external interrupt is pending (if any).
  * Returns: