diff --git a/arch/powerpc/include/asm/kvm_book3s_asm.h b/arch/powerpc/include/asm/kvm_book3s_asm.h
index 1f2f5b6..88609b2 100644
--- a/arch/powerpc/include/asm/kvm_book3s_asm.h
+++ b/arch/powerpc/include/asm/kvm_book3s_asm.h
@@ -79,6 +79,9 @@ struct kvmppc_host_state {
 	u8 napping;
 
 #ifdef CONFIG_KVM_BOOK3S_64_HV
+	u8 hwthread_req;
+	u8 hwthread_state;
+
 	struct kvm_vcpu *kvm_vcpu;
 	struct kvmppc_vcore *kvm_vcore;
 	unsigned long xics_phys;
@@ -122,4 +125,9 @@ struct kvmppc_book3s_shadow_vcpu {
 
 #endif /*__ASSEMBLY__ */
 
+/* Values for kvm_state */
+#define KVM_HWTHREAD_IN_KERNEL	0
+#define KVM_HWTHREAD_IN_NAP	1
+#define KVM_HWTHREAD_IN_KVM	2
+
 #endif /* __ASM_KVM_BOOK3S_ASM_H__ */
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index a24f2c0..7133290 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -554,6 +554,8 @@ int main(void)
 	HSTATE_FIELD(HSTATE_IN_GUEST, in_guest);
 	HSTATE_FIELD(HSTATE_RESTORE_HID5, restore_hid5);
 	HSTATE_FIELD(HSTATE_NAPPING, napping);
+	HSTATE_FIELD(HSTATE_HWTHREAD_REQ, hwthread_req);
+	HSTATE_FIELD(HSTATE_HWTHREAD_STATE, hwthread_state);
 
 #ifdef CONFIG_KVM_BOOK3S_64_HV
 	HSTATE_FIELD(HSTATE_KVM_VCPU, kvm_vcpu);
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 8bea120..e9bd8a2 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -62,11 +62,13 @@ BEGIN_FTR_SECTION
 	GET_PACA(r13)
 
 #ifdef CONFIG_KVM_BOOK3S_64_HV
-	lbz	r0,PACAPROCSTART(r13)
-	cmpwi	r0,0x80
-	bne	1f
-	li	r0,1
-	stb	r0,PACAPROCSTART(r13)
+	li	r0,KVM_HWTHREAD_IN_KERNEL
+	stb	r0,HSTATE_HWTHREAD_STATE(r13)
+	/* Order setting hwthread_state vs. testing hwthread_req */
+	sync
+	lbz	r0,HSTATE_HWTHREAD_REQ(r13)
+	cmpwi	r0,0
+	beq	1f
 	b	kvm_start_guest
 1:
 #endif
diff --git a/arch/powerpc/kernel/idle_power7.S b/arch/powerpc/kernel/idle_power7.S
index fcdff19..95eb8c5 100644
--- a/arch/powerpc/kernel/idle_power7.S
+++ b/arch/powerpc/kernel/idle_power7.S
@@ -15,6 +15,7 @@
 #include <asm/ppc_asm.h>
 #include <asm/asm-offsets.h>
 #include <asm/ppc-opcode.h>
+#include <asm/kvm_book3s_asm.h>
 
 #undef DEBUG
 
@@ -64,6 +65,12 @@ _GLOBAL(power7_idle)
 	std	r9,_MSR(r1)
 	std	r1,PACAR1(r13)
 
+#ifdef CONFIG_KVM_BOOK3S_64_HV
+	/* Tell KVM we're napping */
+	li	r4,KVM_HWTHREAD_IN_NAP
+	stb	r4,HSTATE_HWTHREAD_STATE(r13)
+#endif
+
 	/* Magic NAP mode enter sequence */
 	std	r0,0(r1)
 	ptesync
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index d386b61..1a5aa51 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -568,6 +568,45 @@ static void kvmppc_remove_runnable(struct kvmppc_vcore *vc,
 	list_del(&vcpu->arch.run_list);
 }
 
+static int kvmppc_grab_hwthread(int cpu)
+{
+	struct paca_struct *tpaca;
+	long timeout = 1000;
+
+	tpaca = &paca[cpu];
+
+	/* Ensure the thread won't go into the kernel if it wakes */
+	tpaca->kvm_hstate.hwthread_req = 1;
+
+	/*
+	 * If the thread is already executing in the kernel (e.g. handling
+	 * a stray interrupt), wait for it to get back to nap mode.
+	 * The smp_mb() is to ensure that our setting of hwthread_req
+	 * is visible before we look at hwthread_state, so if this
+	 * races with the code at system_reset_pSeries and the thread
+	 * misses our setting of hwthread_req, we are sure to see its
+	 * setting of hwthread_state, and vice versa.
+	 */
+	smp_mb();
+	while (tpaca->kvm_hstate.hwthread_state == KVM_HWTHREAD_IN_KERNEL) {
+		if (--timeout <= 0) {
+			pr_err("KVM: couldn't grab cpu %d\n", cpu);
+			return -EBUSY;
+		}
+		udelay(1);
+	}
+	return 0;
+}
+
+static void kvmppc_release_hwthread(int cpu)
+{
+	struct paca_struct *tpaca;
+
+	tpaca = &paca[cpu];
+	tpaca->kvm_hstate.hwthread_req = 0;
+	tpaca->kvm_hstate.kvm_vcpu = NULL;
+}
+
 static void kvmppc_start_thread(struct kvm_vcpu *vcpu)
 {
 	int cpu;
@@ -587,8 +626,7 @@ static void kvmppc_start_thread(struct kvm_vcpu *vcpu)
 	smp_wmb();
 #if defined(CONFIG_PPC_ICP_NATIVE) && defined(CONFIG_SMP)
 	if (vcpu->arch.ptid) {
-		tpaca->cpu_start = 0x80;
-		wmb();
+		kvmppc_grab_hwthread(cpu);
 		xics_wake_cpu(cpu);
 		++vc->n_woken;
 	}
@@ -638,7 +676,7 @@ static int kvmppc_run_core(struct kvmppc_vcore *vc)
 	struct kvm_vcpu *vcpu, *vcpu0, *vnext;
 	long ret;
 	u64 now;
-	int ptid;
+	int ptid, i;
 
 	/* don't start if any threads have a signal pending */
 	list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list)
@@ -685,12 +723,17 @@ static int kvmppc_run_core(struct kvmppc_vcore *vc)
 	vc->napping_threads = 0;
 	list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list)
 		kvmppc_start_thread(vcpu);
+	/* Grab any remaining hw threads so they can't go into the kernel */
+	for (i = ptid; i < threads_per_core; ++i)
+		kvmppc_grab_hwthread(vc->pcpu + i);
 
 	preempt_disable();
 	spin_unlock(&vc->lock);
 
 	kvm_guest_enter();
 	__kvmppc_vcore_entry(NULL, vcpu0);
+	for (i = 0; i < threads_per_core; ++i)
+		kvmppc_release_hwthread(vc->pcpu + i);
 
 	spin_lock(&vc->lock);
 	/* disable sending of IPIs on virtual external irqs */
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index b70bf22..d595033 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -26,6 +26,7 @@
 #include <asm/hvcall.h>
 #include <asm/asm-offsets.h>
 #include <asm/exception-64s.h>
+#include <asm/kvm_book3s_asm.h>
 
 /*****************************************************************************
  *                                                                           *
@@ -82,6 +83,7 @@ _GLOBAL(kvmppc_hv_entry_trampoline)
 
 #define XICS_XIRR		4
 #define XICS_QIRR		0xc
+#define XICS_IPI		2	/* interrupt source # for IPIs */
 
 /*
  * We come in here when wakened from nap mode on a secondary hw thread.
@@ -94,26 +96,54 @@ kvm_start_guest:
 	subi	r1,r1,STACK_FRAME_OVERHEAD
 	ld	r2,PACATOC(r13)
 
-	/* were we napping due to cede? */
-	lbz	r0,HSTATE_NAPPING(r13)
-	cmpwi	r0,0
-	bne	kvm_end_cede
+	li	r0,KVM_HWTHREAD_IN_KVM
+	stb	r0,HSTATE_HWTHREAD_STATE(r13)
 
-	/* get vcpu pointer */
-	ld	r4, HSTATE_KVM_VCPU(r13)
+	/* NV GPR values from power7_idle() will no longer be valid */
+	li	r0,1
+	stb	r0,PACA_NAPSTATELOST(r13)
 
-	/* We got here with an IPI; clear it */
-	ld	r5, HSTATE_XICS_PHYS(r13)
-	li	r0, 0xff
-	li	r6, XICS_QIRR
-	li	r7, XICS_XIRR
-	lwzcix	r8, r5, r7		/* ack the interrupt */
+	/* get vcpu pointer, NULL if we have no vcpu to run */
+	ld	r4,HSTATE_KVM_VCPU(r13)
+	cmpdi	cr1,r4,0
+
+	/* Check the wake reason in SRR1 to see why we got here */
+	mfspr	r3,SPRN_SRR1
+	rlwinm	r3,r3,44-31,0x7		/* extract wake reason field */
+	cmpwi	r3,4			/* was it an external interrupt? */
+	bne	27f
+
+	/*
+	 * External interrupt - for now assume it is an IPI, since we
+	 * should never get any other interrupts sent to offline threads.
+	 * Only do this for secondary threads.
+	 */
+	beq	cr1,25f
+	lwz	r3,VCPU_PTID(r4)
+	cmpwi	r3,0
+	beq	27f
+25:	ld	r5,HSTATE_XICS_PHYS(r13)
+	li	r0,0xff
+	li	r6,XICS_QIRR
+	li	r7,XICS_XIRR
+	lwzcix	r8,r5,r7		/* get and ack the interrupt */
 	sync
-	stbcix	r0, r5, r6		/* clear it */
-	stwcix	r8, r5, r7		/* EOI it */
+	clrldi.	r9,r8,40		/* get interrupt source ID. */
+	beq	27f			/* none there? */
+	cmpwi	r9,XICS_IPI
+	bne	26f
+	stbcix	r0,r5,r6		/* clear IPI */
+26:	stwcix	r8,r5,r7		/* EOI the interrupt */
 
-	/* NV GPR values from power7_idle() will no longer be valid */
-	stb	r0, PACA_NAPSTATELOST(r13)
+27:	/* XXX should handle hypervisor maintenance interrupts etc. here */
+
+	/* if we have no vcpu to run, go back to sleep */
+	beq	cr1,kvm_no_guest
+
+	/* were we napping due to cede? */
+	lbz	r0,HSTATE_NAPPING(r13)
+	cmpwi	r0,0
+	bne	kvm_end_cede
 
 .global kvmppc_hv_entry
 kvmppc_hv_entry:
@@ -1445,8 +1475,8 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_206)
 	 * Take a nap until a decrementer or external interrupt occurs,
 	 * with PECE1 (wake on decr) and PECE0 (wake on external) set in LPCR
 	 */
-	li	r0,0x80
-	stb	r0,PACAPROCSTART(r13)
+	li	r0,1
+	stb	r0,HSTATE_HWTHREAD_REQ(r13)
 	mfspr	r5,SPRN_LPCR
 	ori	r5,r5,LPCR_PECE0 | LPCR_PECE1
 	mtspr	SPRN_LPCR,r5
@@ -1463,26 +1493,7 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_206)
 kvm_end_cede:
 	/* Woken by external or decrementer interrupt */
 	ld	r1, HSTATE_HOST_R1(r13)
-	ld	r2, PACATOC(r13)
 
-	/* If we're a secondary thread and we got here by an IPI, ack it */
-	ld	r4,HSTATE_KVM_VCPU(r13)
-	lwz	r3,VCPU_PTID(r4)
-	cmpwi	r3,0
-	beq	27f
-	mfspr	r3,SPRN_SRR1
-	rlwinm	r3,r3,44-31,0x7		/* extract wake reason field */
-	cmpwi	r3,4			/* was it an external interrupt? */
-	bne	27f
-	ld	r5, HSTATE_XICS_PHYS(r13)
-	li	r0,0xff
-	li	r6,XICS_QIRR
-	li	r7,XICS_XIRR
-	lwzcix	r8,r5,r7		/* ack the interrupt */
-	sync
-	stbcix	r0,r5,r6		/* clear it */
-	stwcix	r8,r5,r7		/* EOI it */
-27:
 	/* load up FP state */
 	bl	kvmppc_load_fp
 
@@ -1580,12 +1591,17 @@ secondary_nap:
 	stwcx.	r3, 0, r4
 	bne	51b
 
+kvm_no_guest:
+	li	r0, KVM_HWTHREAD_IN_NAP
+	stb	r0, HSTATE_HWTHREAD_STATE(r13)
+	li	r0, 0
+	std	r0, HSTATE_KVM_VCPU(r13)
+
 	li	r3, LPCR_PECE0
 	mfspr	r4, SPRN_LPCR
 	rlwimi	r4, r3, 0, LPCR_PECE0 | LPCR_PECE1
 	mtspr	SPRN_LPCR, r4
 	isync
-	li	r0, 0
 	std	r0, HSTATE_SCRATCH0(r13)
 	ptesync
 	ld	r0, HSTATE_SCRATCH0(r13)
