diff --git a/arch/powerpc/kvm/book3s_hv_builtin.c b/arch/powerpc/kvm/book3s_hv_builtin.c
index 5f0380d..b476a6a 100644
--- a/arch/powerpc/kvm/book3s_hv_builtin.c
+++ b/arch/powerpc/kvm/book3s_hv_builtin.c
@@ -25,6 +25,7 @@
 #include <asm/xics.h>
 #include <asm/dbell.h>
 #include <asm/cputhreads.h>
+#include <asm/io.h>
 
 #define KVM_CMA_CHUNK_ORDER	18
 
@@ -286,3 +287,86 @@ void kvmhv_commence_exit(int trap)
 
 struct kvmppc_host_rm_ops *kvmppc_host_rm_ops_hv;
 EXPORT_SYMBOL_GPL(kvmppc_host_rm_ops_hv);
+
+/*
+ * Determine what sort of external interrupt is pending (if any).
+ * Returns:
+ *	0 if no interrupt is pending
+ *	1 if an interrupt is pending that needs to be handled by the host
+ *	-1 if there was a guest wakeup IPI (which has now been cleared)
+ */
+
+long kvmppc_read_intr(void)
+{
+	unsigned long xics_phys;
+	u32 h_xirr;
+	__be32 xirr;
+	u32 xisr;
+	u8 host_ipi;
+
+	/* see if a host IPI is pending */
+	host_ipi = local_paca->kvm_hstate.host_ipi;
+	if (host_ipi)
+		return 1;
+
+	/* Now read the interrupt from the ICP */
+	xics_phys = local_paca->kvm_hstate.xics_phys;
+	if (unlikely(!xics_phys))
+		return 1;
+
+	/*
+	 * Save XIRR for later. Since we get control in reverse endian
+	 * on LE systems, save it byte reversed and fetch it back in
+	 * host endian. Note that xirr is the value read from the
+	 * XIRR register, while h_xirr is the host endian version.
+	 */
+	xirr = _lwzcix(xics_phys + XICS_XIRR);
+	h_xirr = be32_to_cpu(xirr);
+	local_paca->kvm_hstate.saved_xirr = h_xirr;
+	xisr = h_xirr & 0xffffff;
+	/*
+	 * Ensure that the store/load complete to guarantee all side
+	 * effects of loading from XIRR has completed
+	 */
+	smp_mb();
+
+	/* if nothing pending in the ICP */
+	if (!xisr)
+		return 0;
+
+	/* We found something in the ICP...
+	 *
+	 * If it is an IPI, clear the MFRR and EOI it.
+	 */
+	if (xisr == XICS_IPI) {
+		_stbcix(xics_phys + XICS_MFRR, 0xff);
+		_stwcix(xics_phys + XICS_XIRR, xirr);
+		/*
+		 * Need to ensure side effects of above stores
+		 * complete before proceeding.
+		 */
+		smp_mb();
+
+		/*
+		 * We need to re-check host IPI now in case it got set in the
+		 * meantime. If it's clear, we bounce the interrupt to the
+		 * guest
+		 */
+		host_ipi = local_paca->kvm_hstate.host_ipi;
+		if (unlikely(host_ipi != 0)) {
+			/* We raced with the host,
+			 * we need to resend that IPI, bummer
+			 */
+			_stbcix(xics_phys + XICS_MFRR, IPI_PRIORITY);
+			/* Let side effects complete */
+			smp_mb();
+			return 1;
+		}
+
+		/* OK, it's an IPI for us */
+		local_paca->kvm_hstate.saved_xirr = 0;
+		return -1;
+	}
+
+	return 1;
+}
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 9756555..dccfa85 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -221,6 +221,13 @@ kvmppc_primary_no_guest:
 	li	r3, 0		/* Don't wake on privileged (OS) doorbell */
 	b	kvm_do_nap
 
+/*
+ * kvm_novcpu_wakeup
+ *	Entered from kvm_start_guest if kvm_hstate.napping is set
+ *	to NAPPING_NOVCPU
+ *		r2 = kernel TOC
+ *		r13 = paca
+ */
 kvm_novcpu_wakeup:
 	ld	r1, HSTATE_HOST_R1(r13)
 	ld	r5, HSTATE_KVM_VCORE(r13)
@@ -230,6 +237,13 @@ kvm_novcpu_wakeup:
 	/* check the wake reason */
 	bl	kvmppc_check_wake_reason
 
+	/*
+	 * Restore volatile registers since we could have called
+	 * a C routine in kvmppc_check_wake_reason.
+	 *	r5 = VCORE
+	 */
+	ld	r5, HSTATE_KVM_VCORE(r13)
+
 	/* see if any other thread is already exiting */
 	lwz	r0, VCORE_ENTRY_EXIT(r5)
 	cmpwi	r0, 0x100
@@ -322,6 +336,11 @@ kvm_start_guest:
 
 	/* Check the wake reason in SRR1 to see why we got here */
 	bl	kvmppc_check_wake_reason
+	/*
+	 * kvmppc_check_wake_reason could invoke a C routine, but we
+	 * have no volatile registers to restore when we return.
+	 */
+
 	cmpdi	r3, 0
 	bge	kvm_no_guest
 
@@ -881,6 +900,7 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
 	cmpwi	r3, 512		/* 1 microsecond */
 	blt	hdec_soon
 
+deliver_guest_interrupt:
 	ld	r6, VCPU_CTR(r4)
 	ld	r7, VCPU_XER(r4)
 
@@ -895,7 +915,6 @@ kvmppc_cede_reentry:		/* r4 = vcpu, r13 = paca */
 	mtspr	SPRN_SRR0, r6
 	mtspr	SPRN_SRR1, r7
 
-deliver_guest_interrupt:
 	/* r11 = vcpu->arch.msr & ~MSR_HV */
 	rldicl	r11, r11, 63 - MSR_HV_LG, 1
 	rotldi	r11, r11, 1 + MSR_HV_LG
@@ -1155,10 +1174,36 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
 	 * set, we know the host wants us out so let's do it now
 	 */
 	bl	kvmppc_read_intr
+
+	/*
+	 * Restore the active volatile registers after returning from
+	 * a C function.
+	 */
+	ld	r9, HSTATE_KVM_VCPU(r13)
+	li	r12, BOOK3S_INTERRUPT_EXTERNAL
+
+	/*
+	 * kvmppc_read_intr return codes:
+	 *
+	 * Exit to host (r3 > 0)
+	 *   1 An interrupt is pending that needs to be handled by the host
+	 *     Exit guest and return to host by branching to guest_exit_cont
+	 *
+	 * Before returning to guest, we check if any CPU is heading out
+	 * to the host and if so, we head out also. If no CPUs are heading
+	 * check return values <= 0.
+	 *
+	 * Return to guest (r3 <= 0)
+	 *  0 No external interrupt is pending
+	 * -1 A guest wakeup IPI (which has now been cleared)
+	 *    In either case, we return to guest to deliver any pending
+	 *    guest interrupts.
+	 */
+
 	cmpdi	r3, 0
 	bgt	guest_exit_cont
 
-	/* Check if any CPU is heading out to the host, if so head out too */
+	/* Return code <= 0 */
 4:	ld	r5, HSTATE_KVM_VCORE(r13)
 	lwz	r0, VCORE_ENTRY_EXIT(r5)
 	cmpwi	r0, 0x100
@@ -2213,10 +2258,20 @@ END_FTR_SECTION_IFSET(CPU_FTR_TM)
 	ld	r29, VCPU_GPR(R29)(r4)
 	ld	r30, VCPU_GPR(R30)(r4)
 	ld	r31, VCPU_GPR(R31)(r4)
- 
+
 	/* Check the wake reason in SRR1 to see why we got here */
 	bl	kvmppc_check_wake_reason
 
+	/*
+	 * Restore volatile registers since we could have called a
+	 * C routine in kvmppc_check_wake_reason
+	 *	r4 = VCPU
+	 * r3 tells us whether we need to return to host or not
+	 * WARNING: it gets checked further down:
+	 * should not modify r3 until this check is done.
+	 */
+	ld	r4, HSTATE_KVM_VCPU(r13)
+
 	/* clear our bit in vcore->napping_threads */
 34:	ld	r5,HSTATE_KVM_VCORE(r13)
 	lbz	r7,HSTATE_PTID(r13)
@@ -2230,7 +2285,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_TM)
 	li	r0,0
 	stb	r0,HSTATE_NAPPING(r13)
 
-	/* See if the wake reason means we need to exit */
+	/* See if the wake reason saved in r3 means we need to exit */
 	stw	r12, VCPU_TRAP(r4)
 	mr	r9, r4
 	cmpdi	r3, 0
@@ -2300,7 +2355,9 @@ machine_check_realmode:
  *
  * Also sets r12 to the interrupt vector for any interrupt that needs
  * to be handled now by the host (0x500 for external interrupt), or zero.
- * Modifies r0, r6, r7, r8.
+ * Modifies all volatile registers (since it may call a C function).
+ * This routine calls kvmppc_read_intr, a C function, if an external
+ * interrupt is pending.
  */
 kvmppc_check_wake_reason:
 	mfspr	r6, SPRN_SRR1
@@ -2310,8 +2367,7 @@ FTR_SECTION_ELSE
 	rlwinm	r6, r6, 45-31, 0xe	/* P7 wake reason field is 3 bits */
 ALT_FTR_SECTION_END_IFSET(CPU_FTR_ARCH_207S)
 	cmpwi	r6, 8			/* was it an external interrupt? */
-	li	r12, BOOK3S_INTERRUPT_EXTERNAL
-	beq	kvmppc_read_intr	/* if so, see what it was */
+	beq	7f			/* if so, see what it was */
 	li	r3, 0
 	li	r12, 0
 	cmpwi	r6, 6			/* was it the decrementer? */
@@ -2350,83 +2406,17 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 	li	r3, 1
 	blr
 
-/*
- * Determine what sort of external interrupt is pending (if any).
- * Returns:
- *	0 if no interrupt is pending
- *	1 if an interrupt is pending that needs to be handled by the host
- *	-1 if there was a guest wakeup IPI (which has now been cleared)
- * Modifies r0, r6, r7, r8, returns value in r3.
- */
-kvmppc_read_intr:
-	/* see if a host IPI is pending */
-	li	r3, 1
-	lbz	r0, HSTATE_HOST_IPI(r13)
-	cmpwi	r0, 0
-	bne	1f
-
-	/* Now read the interrupt from the ICP */
-	ld	r6, HSTATE_XICS_PHYS(r13)
-	li	r7, XICS_XIRR
-	cmpdi	r6, 0
-	beq-	1f
-	lwzcix	r0, r6, r7
-	/*
-	 * Save XIRR for later. Since we get in in reverse endian on LE
-	 * systems, save it byte reversed and fetch it back in host endian.
-	 */
-	li	r3, HSTATE_SAVED_XIRR
-	STWX_BE	r0, r3, r13
-#ifdef __LITTLE_ENDIAN__
-	lwz	r3, HSTATE_SAVED_XIRR(r13)
-#else
-	mr	r3, r0
-#endif
-	rlwinm.	r3, r3, 0, 0xffffff
-	sync
-	beq	1f			/* if nothing pending in the ICP */
-
-	/* We found something in the ICP...
-	 *
-	 * If it's not an IPI, stash it in the PACA and return to
-	 * the host, we don't (yet) handle directing real external
-	 * interrupts directly to the guest
-	 */
-	cmpwi	r3, XICS_IPI		/* if there is, is it an IPI? */
-	bne	42f
-
-	/* It's an IPI, clear the MFRR and EOI it */
-	li	r3, 0xff
-	li	r8, XICS_MFRR
-	stbcix	r3, r6, r8		/* clear the IPI */
-	stwcix	r0, r6, r7		/* EOI it */
-	sync
-
-	/* We need to re-check host IPI now in case it got set in the
-	 * meantime. If it's clear, we bounce the interrupt to the
-	 * guest
-	 */
-	lbz	r0, HSTATE_HOST_IPI(r13)
-	cmpwi	r0, 0
-	bne-	43f
-
-	/* OK, it's an IPI for us */
-	li	r12, 0
-	li	r3, -1
-1:	blr
-
-42:	/* It's not an IPI and it's for the host. We saved a copy of XIRR in
-	 * the PACA earlier, it will be picked up by the host ICP driver
-	 */
-	li	r3, 1
-	b	1b
-
-43:	/* We raced with the host, we need to resend that IPI, bummer */
-	li	r0, IPI_PRIORITY
-	stbcix	r0, r6, r8		/* set the IPI */
-	sync
-	li	r3, 1
-	b	1b
+	/* external interrupt - create a stack frame so we can call C */
+7:	mflr	r0
+	std	r0, PPC_LR_STKOFF(r1)
+	stdu	r1, -PPC_MIN_STKFRM(r1)
+	bl	kvmppc_read_intr
+	nop
+	li	r12, BOOK3S_INTERRUPT_EXTERNAL
+	ld	r0, PPC_MIN_STKFRM+PPC_LR_STKOFF(r1)
+	addi	r1, r1, PPC_MIN_STKFRM
+	mtlr	r0
+	blr
 
 /*
  * Save away FP, VMX and VSX registers.
