diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index f1d0bbc..d2068bb 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -369,6 +369,14 @@ struct kvmppc_slb {
 	u8 base_page_size;	/* MMU_PAGE_xxx */
 };
 
+/* Struct used to accumulate timing information in HV real mode code */
+struct kvmhv_tb_accumulator {
+	u64	seqcount;	/* used to synchronize access, also count * 2 */
+	u64	tb_total;	/* total time in timebase ticks */
+	u64	tb_min;		/* min time */
+	u64	tb_max;		/* max time */
+};
+
 # ifdef CONFIG_PPC_FSL_BOOK3E
 #define KVMPPC_BOOKE_IAC_NUM	2
 #define KVMPPC_BOOKE_DAC_NUM	2
@@ -657,6 +665,19 @@ struct kvm_vcpu_arch {
 
 	u32 emul_inst;
 #endif
+
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+	struct kvmhv_tb_accumulator *cur_activity;	/* What we're timing */
+	u64	cur_tb_start;			/* when it started */
+	struct kvmhv_tb_accumulator rm_entry;	/* real-mode entry code */
+	struct kvmhv_tb_accumulator rm_intr;	/* real-mode intr handling */
+	struct kvmhv_tb_accumulator rm_exit;	/* real-mode exit code */
+	struct kvmhv_tb_accumulator guest_time;	/* guest execution */
+	struct kvmhv_tb_accumulator cede_time;	/* time napping inside guest */
+
+	struct dentry *debugfs_dir;
+	struct dentry *debugfs_timings;
+#endif /* CONFIG_KVM_BOOK3S_HV_EXIT_TIMING */
 };
 
 #define VCPU_FPR(vcpu, i)	(vcpu)->arch.fp.fpr[i][TS_FPROFFSET]
diff --git a/arch/powerpc/include/asm/time.h b/arch/powerpc/include/asm/time.h
index 03cbada..10fc784 100644
--- a/arch/powerpc/include/asm/time.h
+++ b/arch/powerpc/include/asm/time.h
@@ -211,5 +211,8 @@ extern void secondary_cpu_time_init(void);
 
 DECLARE_PER_CPU(u64, decrementers_next_tb);
 
+/* Convert timebase ticks to nanoseconds */
+unsigned long long tb_to_ns(unsigned long long tb_ticks);
+
 #endif /* __KERNEL__ */
 #endif /* __POWERPC_TIME_H */
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 4717859..3fea721 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -459,6 +459,19 @@ int main(void)
 	DEFINE(VCPU_SPRG2, offsetof(struct kvm_vcpu, arch.shregs.sprg2));
 	DEFINE(VCPU_SPRG3, offsetof(struct kvm_vcpu, arch.shregs.sprg3));
 #endif
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+	DEFINE(VCPU_TB_RMENTRY, offsetof(struct kvm_vcpu, arch.rm_entry));
+	DEFINE(VCPU_TB_RMINTR, offsetof(struct kvm_vcpu, arch.rm_intr));
+	DEFINE(VCPU_TB_RMEXIT, offsetof(struct kvm_vcpu, arch.rm_exit));
+	DEFINE(VCPU_TB_GUEST, offsetof(struct kvm_vcpu, arch.guest_time));
+	DEFINE(VCPU_TB_CEDE, offsetof(struct kvm_vcpu, arch.cede_time));
+	DEFINE(VCPU_CUR_ACTIVITY, offsetof(struct kvm_vcpu, arch.cur_activity));
+	DEFINE(VCPU_ACTIVITY_START, offsetof(struct kvm_vcpu, arch.cur_tb_start));
+	DEFINE(TAS_SEQCOUNT, offsetof(struct kvmhv_tb_accumulator, seqcount));
+	DEFINE(TAS_TOTAL, offsetof(struct kvmhv_tb_accumulator, tb_total));
+	DEFINE(TAS_MIN, offsetof(struct kvmhv_tb_accumulator, tb_min));
+	DEFINE(TAS_MAX, offsetof(struct kvmhv_tb_accumulator, tb_max));
+#endif
 	DEFINE(VCPU_SHARED_SPRG3, offsetof(struct kvm_vcpu_arch_shared, sprg3));
 	DEFINE(VCPU_SHARED_SPRG4, offsetof(struct kvm_vcpu_arch_shared, sprg4));
 	DEFINE(VCPU_SHARED_SPRG5, offsetof(struct kvm_vcpu_arch_shared, sprg5));
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 2d7b33f..56f4484 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -608,6 +608,12 @@ void arch_suspend_enable_irqs(void)
 }
 #endif
 
+unsigned long long tb_to_ns(unsigned long long ticks)
+{
+	return mulhdu(ticks, tb_to_ns_scale) << tb_to_ns_shift;
+}
+EXPORT_SYMBOL_GPL(tb_to_ns);
+
 /*
  * Scheduler clock - returns current time in nanosec units.
  *
diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
index 11850f3..2963e4d 100644
--- a/arch/powerpc/kvm/Kconfig
+++ b/arch/powerpc/kvm/Kconfig
@@ -110,6 +110,20 @@ config KVM_BOOK3S_64_PR
 	  processor, including emulating 32-bit processors on a 64-bit
 	  host.
 
+config KVM_BOOK3S_HV_EXIT_TIMING
+	bool "Detailed timing for hypervisor real-mode code"
+	depends on KVM_BOOK3S_HV_POSSIBLE && DEBUG_FS
+	---help---
+	  Calculate time taken for each vcpu in the real-mode guest entry,
+	  exit, and interrupt handling code, plus time spent in the guest
+	  and in nap mode due to idle (cede) while other threads are still
+	  in the guest.  The total, minimum and maximum times in nanoseconds
+	  together with the number of executions are reported in debugfs in
+	  kvm/vm#/vcpu#/timings.  The overhead is of the order of 30 - 40
+	  ns per exit on POWER8.
+
+	  If unsure, say N.
+
 config KVM_BOOKE_HV
 	bool
 
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index cb54d90..c7b18ac 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1423,6 +1423,154 @@ static struct kvmppc_vcore *kvmppc_vcore_create(struct kvm *kvm, int core)
 	return vcore;
 }
 
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+static struct debugfs_timings_element {
+	const char *name;
+	size_t offset;
+} timings[] = {
+	{"rm_entry",	offsetof(struct kvm_vcpu, arch.rm_entry)},
+	{"rm_intr",	offsetof(struct kvm_vcpu, arch.rm_intr)},
+	{"rm_exit",	offsetof(struct kvm_vcpu, arch.rm_exit)},
+	{"guest",	offsetof(struct kvm_vcpu, arch.guest_time)},
+	{"cede",	offsetof(struct kvm_vcpu, arch.cede_time)},
+};
+
+#define N_TIMINGS	(sizeof(timings) / sizeof(timings[0]))
+
+struct debugfs_timings_state {
+	struct kvm_vcpu	*vcpu;
+	unsigned int	buflen;
+	char		buf[N_TIMINGS * 100];
+};
+
+static int debugfs_timings_open(struct inode *inode, struct file *file)
+{
+	struct kvm_vcpu *vcpu = inode->i_private;
+	struct debugfs_timings_state *p;
+
+	p = kzalloc(sizeof(*p), GFP_KERNEL);
+	if (!p)
+		return -ENOMEM;
+
+	kvm_get_kvm(vcpu->kvm);
+	p->vcpu = vcpu;
+	file->private_data = p;
+
+	return nonseekable_open(inode, file);
+}
+
+static int debugfs_timings_release(struct inode *inode, struct file *file)
+{
+	struct debugfs_timings_state *p = file->private_data;
+
+	kvm_put_kvm(p->vcpu->kvm);
+	kfree(p);
+	return 0;
+}
+
+static ssize_t debugfs_timings_read(struct file *file, char __user *buf,
+				    size_t len, loff_t *ppos)
+{
+	struct debugfs_timings_state *p = file->private_data;
+	struct kvm_vcpu *vcpu = p->vcpu;
+	char *s, *buf_end;
+	struct kvmhv_tb_accumulator tb;
+	u64 count;
+	loff_t pos;
+	ssize_t n;
+	int i, loops;
+	bool ok;
+
+	if (!p->buflen) {
+		s = p->buf;
+		buf_end = s + sizeof(p->buf);
+		for (i = 0; i < N_TIMINGS; ++i) {
+			struct kvmhv_tb_accumulator *acc;
+
+			acc = (struct kvmhv_tb_accumulator *)
+				((unsigned long)vcpu + timings[i].offset);
+			ok = false;
+			for (loops = 0; loops < 1000; ++loops) {
+				count = acc->seqcount;
+				if (!(count & 1)) {
+					smp_rmb();
+					tb = *acc;
+					smp_rmb();
+					if (count == acc->seqcount) {
+						ok = true;
+						break;
+					}
+				}
+				udelay(1);
+			}
+			if (!ok)
+				snprintf(s, buf_end - s, "%s: stuck\n",
+					timings[i].name);
+			else
+				snprintf(s, buf_end - s,
+					"%s: %llu %llu %llu %llu\n",
+					timings[i].name, count / 2,
+					tb_to_ns(tb.tb_total),
+					tb_to_ns(tb.tb_min),
+					tb_to_ns(tb.tb_max));
+			s += strlen(s);
+		}
+		p->buflen = s - p->buf;
+	}
+
+	pos = *ppos;
+	if (pos >= p->buflen)
+		return 0;
+	if (len > p->buflen - pos)
+		len = p->buflen - pos;
+	n = copy_to_user(buf, p->buf + pos, len);
+	if (n) {
+		if (n == len)
+			return -EFAULT;
+		len -= n;
+	}
+	*ppos = pos + len;
+	return len;
+}
+
+static ssize_t debugfs_timings_write(struct file *file, const char __user *buf,
+				     size_t len, loff_t *ppos)
+{
+	return -EACCES;
+}
+
+static const struct file_operations debugfs_timings_ops = {
+	.owner	 = THIS_MODULE,
+	.open	 = debugfs_timings_open,
+	.release = debugfs_timings_release,
+	.read	 = debugfs_timings_read,
+	.write	 = debugfs_timings_write,
+	.llseek	 = generic_file_llseek,
+};
+
+/* Create a debugfs directory for the vcpu */
+static void debugfs_vcpu_init(struct kvm_vcpu *vcpu, unsigned int id)
+{
+	char buf[16];
+	struct kvm *kvm = vcpu->kvm;
+
+	snprintf(buf, sizeof(buf), "vcpu%u", id);
+	if (IS_ERR_OR_NULL(kvm->arch.debugfs_dir))
+		return;
+	vcpu->arch.debugfs_dir = debugfs_create_dir(buf, kvm->arch.debugfs_dir);
+	if (IS_ERR_OR_NULL(vcpu->arch.debugfs_dir))
+		return;
+	vcpu->arch.debugfs_timings =
+		debugfs_create_file("timings", 0444, vcpu->arch.debugfs_dir,
+				    vcpu, &debugfs_timings_ops);
+}
+
+#else /* CONFIG_KVM_BOOK3S_HV_EXIT_TIMING */
+static void debugfs_vcpu_init(struct kvm_vcpu *vcpu, unsigned int id)
+{
+}
+#endif /* CONFIG_KVM_BOOK3S_HV_EXIT_TIMING */
+
 static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm,
 						   unsigned int id)
 {
@@ -1492,6 +1640,8 @@ static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm,
 	vcpu->arch.cpu_type = KVM_CPU_3S_64;
 	kvmppc_sanity_check(vcpu);
 
+	debugfs_vcpu_init(vcpu, id);
+
 	return vcpu;
 
 free_vcpu:
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index e9c3cb5..ee6ba4c 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -225,7 +225,13 @@ kvm_novcpu_wakeup:
 	/* Got an IPI but other vcpus aren't yet exiting, must be a latecomer */
 	ld	r4, HSTATE_KVM_VCPU(r13)
 	cmpdi	r4, 0
-	bne	kvmppc_got_guest
+	beq	kvmppc_primary_no_guest
+
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+	addi	r3, r4, VCPU_TB_RMENTRY
+	bl	kvmhv_start_timing
+#endif
+	b	kvmppc_got_guest
 
 kvm_novcpu_exit:
 	b	hdec_soon
@@ -376,6 +382,14 @@ kvmppc_hv_entry:
 	li	r6, KVM_GUEST_MODE_HOST_HV
 	stb	r6, HSTATE_IN_GUEST(r13)
 
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+	/* Store initial timestamp */
+	cmpdi	r4, 0
+	beq	1f
+	addi	r3, r4, VCPU_TB_RMENTRY
+	bl	kvmhv_start_timing
+1:
+#endif
 	/* Clear out SLB */
 	li	r6,0
 	slbmte	r6,r6
@@ -880,6 +894,12 @@ fast_guest_return:
 	li	r9, KVM_GUEST_MODE_GUEST_HV
 	stb	r9, HSTATE_IN_GUEST(r13)
 
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+	/* Accumulate timing */
+	addi	r3, r4, VCPU_TB_GUEST
+	bl	kvmhv_accumulate_time
+#endif
+
 	/* Enter guest */
 
 BEGIN_FTR_SECTION
@@ -917,6 +937,23 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
 	hrfid
 	b	.
 
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+secondary_too_late:
+	cmpdi	r4, 0
+	beq	11f
+	addi	r3, r4, VCPU_TB_RMEXIT
+	bl	kvmhv_accumulate_time
+11:	b	kvmhv_switch_to_host
+
+hdec_soon:
+	ld	r4, HSTATE_KVM_VCPU(r13)
+	cmpdi	r4, 0
+	beq	12f
+	addi	r3, r4, VCPU_TB_RMEXIT
+	bl	kvmhv_accumulate_time
+12:	b	kvmhv_do_exit
+#endif
+
 /******************************************************************************
  *                                                                            *
  *                               Exit code                                    *
@@ -1002,6 +1039,16 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
 
 	stw	r12,VCPU_TRAP(r9)
 
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+	addi	r3, r9, VCPU_TB_RMINTR
+	mr	r4, r9
+	bl	kvmhv_accumulate_time
+	ld	r5, VCPU_GPR(R5)(r9)
+	ld	r6, VCPU_GPR(R6)(r9)
+	ld	r7, VCPU_GPR(R7)(r9)
+	ld	r8, VCPU_GPR(R8)(r9)
+#endif
+
 	/* Save HEIR (HV emulation assist reg) in emul_inst
 	   if this is an HEI (HV emulation interrupt, e40) */
 	li	r3,KVM_INST_FETCH_FAILED
@@ -1072,6 +1119,11 @@ guest_exit_cont:		/* r9 = vcpu, r12 = trap, r13 = paca */
 	cmpwi	r12, BOOK3S_INTERRUPT_MACHINE_CHECK
 	beq	machine_check_realmode
 mc_cont:
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+	addi	r3, r9, VCPU_TB_RMEXIT
+	mr	r4, r9
+	bl	kvmhv_accumulate_time
+#endif
 
 	/* Save guest CTRL register, set runlatch to 1 */
 6:	mfspr	r6,SPRN_CTRLF
@@ -1416,7 +1468,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 	slbia
 	ptesync
 
-hdec_soon:			/* r12 = trap, r13 = paca */
+#ifndef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+hdec_soon:
+#endif
+kvmhv_do_exit:			/* r12 = trap, r13 = paca */
 	/*
 	 * POWER7/POWER8 guest -> host partition switch code.
 	 * We don't have to lock against tlbies but we do
@@ -1475,7 +1530,10 @@ hdec_soon:			/* r12 = trap, r13 = paca */
 	addi	r6,r6,PACA_SIZE
 	bne	42b
 
+#ifndef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
 secondary_too_late:
+#endif
+kvmhv_switch_to_host:
 	/* Secondary threads wait for primary to do partition switch */
 43:	ld	r5,HSTATE_KVM_VCORE(r13)
 	ld	r4,VCORE_KVM(r5)	/* pointer to struct kvm */
@@ -1561,6 +1619,15 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 1:	addi	r8,r8,16
 	.endr
 
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+	/* Finish timing, if we have a vcpu */
+	ld	r4, HSTATE_KVM_VCPU(r13)
+	cmpdi	r4, 0
+	li	r3, 0
+	beq	2f
+	bl	kvmhv_accumulate_time
+2:
+#endif
 	/* Unset guest mode */
 	li	r0, KVM_GUEST_MODE_NONE
 	stb	r0, HSTATE_IN_GUEST(r13)
@@ -2068,6 +2135,12 @@ _GLOBAL(kvmppc_h_cede)
 	/* save FP state */
 	bl	kvmppc_save_fp
 
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+	ld	r4, HSTATE_KVM_VCPU(r13)
+	addi	r3, r4, VCPU_TB_CEDE
+	bl	kvmhv_accumulate_time
+#endif
+
 	/*
 	 * Take a nap until a decrementer or external or doobell interrupt
 	 * occurs, with PECE1, PECE0 and PECEDP set in LPCR. Also clear the
@@ -2108,6 +2181,11 @@ kvm_end_cede:
 	/* Woken by external or decrementer interrupt */
 	ld	r1, HSTATE_HOST_R1(r13)
 
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+	addi	r3, r4, VCPU_TB_RMINTR
+	bl	kvmhv_accumulate_time
+#endif
+
 	/* load up FP state */
 	bl	kvmppc_load_fp
 
@@ -2428,3 +2506,50 @@ kvmppc_fix_pmao:
 	mtspr	SPRN_PMC6, r3
 	isync
 	blr
+
+#ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
+/*
+ * Start timing an activity
+ * r3 = pointer to time accumulation struct, r4 = vcpu
+ */
+kvmhv_start_timing:
+	mftb	r5
+	std	r3, VCPU_CUR_ACTIVITY(r4)
+	std	r5, VCPU_ACTIVITY_START(r4)
+	blr
+
+/*
+ * Accumulate time to one activity and start another.
+ * r3 = pointer to new time accumulation struct, r4 = vcpu
+ */
+kvmhv_accumulate_time:
+	ld	r5, VCPU_CUR_ACTIVITY(r4)
+	ld	r6, VCPU_ACTIVITY_START(r4)
+	std	r3, VCPU_CUR_ACTIVITY(r4)
+	mftb	r7
+	std	r7, VCPU_ACTIVITY_START(r4)
+	cmpdi	r5, 0
+	beqlr
+	subf	r3, r6, r7
+	ld	r8, TAS_SEQCOUNT(r5)
+	cmpdi	r8, 0
+	addi	r8, r8, 1
+	std	r8, TAS_SEQCOUNT(r5)
+	lwsync
+	ld	r7, TAS_TOTAL(r5)
+	add	r7, r7, r3
+	std	r7, TAS_TOTAL(r5)
+	ld	r6, TAS_MIN(r5)
+	ld	r7, TAS_MAX(r5)
+	beq	3f
+	cmpd	r3, r6
+	bge	1f
+3:	std	r3, TAS_MIN(r5)
+1:	cmpd	r3, r7
+	ble	2f
+	std	r3, TAS_MAX(r5)
+2:	lwsync
+	addi	r8, r8, 1
+	std	r8, TAS_SEQCOUNT(r5)
+	blr
+#endif
