Initial import

1 files changed, 849 insertions, 0 deletions

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
new file mode 100644
index 000000000..943562006
--- /dev/null
+++ b/arch/x86/kernel/kvm.c
@@ -0,0 +1,849 @@
+/*
+ * KVM paravirt_ops implementation
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ * Copyright (C) 2007, Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
+ * Copyright IBM Corporation, 2007
+ *   Authors: Anthony Liguori <aliguori@us.ibm.com>
+ */
+
+#include <linux/context_tracking.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/kvm_para.h>
+#include <linux/cpu.h>
+#include <linux/mm.h>
+#include <linux/highmem.h>
+#include <linux/hardirq.h>
+#include <linux/notifier.h>
+#include <linux/reboot.h>
+#include <linux/hash.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/kprobes.h>
+#include <linux/debugfs.h>
+#include <linux/nmi.h>
+#include <asm/timer.h>
+#include <asm/cpu.h>
+#include <asm/traps.h>
+#include <asm/desc.h>
+#include <asm/tlbflush.h>
+#include <asm/idle.h>
+#include <asm/apic.h>
+#include <asm/apicdef.h>
+#include <asm/hypervisor.h>
+#include <asm/kvm_guest.h>
+
+static int kvmapf = 1;
+
+static int parse_no_kvmapf(char *arg)
+{
+        kvmapf = 0;
+        return 0;
+}
+
+early_param("no-kvmapf", parse_no_kvmapf);
+
+static int steal_acc = 1;
+static int parse_no_stealacc(char *arg)
+{
+        steal_acc = 0;
+        return 0;
+}
+
+early_param("no-steal-acc", parse_no_stealacc);
+
+static int kvmclock_vsyscall = 1;
+static int parse_no_kvmclock_vsyscall(char *arg)
+{
+        kvmclock_vsyscall = 0;
+        return 0;
+}
+
+early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall);
+
+static DEFINE_PER_CPU(struct kvm_vcpu_pv_apf_data, apf_reason) __aligned(64);
+static DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
+static int has_steal_clock = 0;
+
+/*
+ * No need for any "IO delay" on KVM
+ */
+static void kvm_io_delay(void)
+{
+}
+
+#define KVM_TASK_SLEEP_HASHBITS 8
+#define KVM_TASK_SLEEP_HASHSIZE (1<<KVM_TASK_SLEEP_HASHBITS)
+
+struct kvm_task_sleep_node {
+	struct hlist_node link;
+	wait_queue_head_t wq;
+	u32 token;
+	int cpu;
+	bool halted;
+};
+
+static struct kvm_task_sleep_head {
+	spinlock_t lock;
+	struct hlist_head list;
+} async_pf_sleepers[KVM_TASK_SLEEP_HASHSIZE];
+
+static struct kvm_task_sleep_node *_find_apf_task(struct kvm_task_sleep_head *b,
+						  u32 token)
+{
+	struct hlist_node *p;
+
+	hlist_for_each(p, &b->list) {
+		struct kvm_task_sleep_node *n =
+			hlist_entry(p, typeof(*n), link);
+		if (n->token == token)
+			return n;
+	}
+
+	return NULL;
+}
+
+void kvm_async_pf_task_wait(u32 token)
+{
+	u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS);
+	struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
+	struct kvm_task_sleep_node n, *e;
+	DEFINE_WAIT(wait);
+
+	rcu_irq_enter();
+
+	spin_lock(&b->lock);
+	e = _find_apf_task(b, token);
+	if (e) {
+		/* dummy entry exist -> wake up was delivered ahead of PF */
+		hlist_del(&e->link);
+		kfree(e);
+		spin_unlock(&b->lock);
+
+		rcu_irq_exit();
+		return;
+	}
+
+	n.token = token;
+	n.cpu = smp_processor_id();
+	n.halted = is_idle_task(current) || preempt_count() > 1;
+	init_waitqueue_head(&n.wq);
+	hlist_add_head(&n.link, &b->list);
+	spin_unlock(&b->lock);
+
+	for (;;) {
+		if (!n.halted)
+			prepare_to_wait(&n.wq, &wait, TASK_UNINTERRUPTIBLE);
+		if (hlist_unhashed(&n.link))
+			break;
+
+		if (!n.halted) {
+			local_irq_enable();
+			schedule();
+			local_irq_disable();
+		} else {
+			/*
+			 * We cannot reschedule. So halt.
+			 */
+			rcu_irq_exit();
+			native_safe_halt();
+			rcu_irq_enter();
+			local_irq_disable();
+		}
+	}
+	if (!n.halted)
+		finish_wait(&n.wq, &wait);
+
+	rcu_irq_exit();
+	return;
+}
+EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait);
+
+static void apf_task_wake_one(struct kvm_task_sleep_node *n)
+{
+	hlist_del_init(&n->link);
+	if (n->halted)
+		smp_send_reschedule(n->cpu);
+	else if (waitqueue_active(&n->wq))
+		wake_up(&n->wq);
+}
+
+static void apf_task_wake_all(void)
+{
+	int i;
+
+	for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++) {
+		struct hlist_node *p, *next;
+		struct kvm_task_sleep_head *b = &async_pf_sleepers[i];
+		spin_lock(&b->lock);
+		hlist_for_each_safe(p, next, &b->list) {
+			struct kvm_task_sleep_node *n =
+				hlist_entry(p, typeof(*n), link);
+			if (n->cpu == smp_processor_id())
+				apf_task_wake_one(n);
+		}
+		spin_unlock(&b->lock);
+	}
+}
+
+void kvm_async_pf_task_wake(u32 token)
+{
+	u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS);
+	struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
+	struct kvm_task_sleep_node *n;
+
+	if (token == ~0) {
+		apf_task_wake_all();
+		return;
+	}
+
+again:
+	spin_lock(&b->lock);
+	n = _find_apf_task(b, token);
+	if (!n) {
+		/*
+		 * async PF was not yet handled.
+		 * Add dummy entry for the token.
+		 */
+		n = kzalloc(sizeof(*n), GFP_ATOMIC);
+		if (!n) {
+			/*
+			 * Allocation failed! Busy wait while other cpu
+			 * handles async PF.
+			 */
+			spin_unlock(&b->lock);
+			cpu_relax();
+			goto again;
+		}
+		n->token = token;
+		n->cpu = smp_processor_id();
+		init_waitqueue_head(&n->wq);
+		hlist_add_head(&n->link, &b->list);
+	} else
+		apf_task_wake_one(n);
+	spin_unlock(&b->lock);
+	return;
+}
+EXPORT_SYMBOL_GPL(kvm_async_pf_task_wake);
+
+u32 kvm_read_and_reset_pf_reason(void)
+{
+	u32 reason = 0;
+
+	if (__this_cpu_read(apf_reason.enabled)) {
+		reason = __this_cpu_read(apf_reason.reason);
+		__this_cpu_write(apf_reason.reason, 0);
+	}
+
+	return reason;
+}
+EXPORT_SYMBOL_GPL(kvm_read_and_reset_pf_reason);
+NOKPROBE_SYMBOL(kvm_read_and_reset_pf_reason);
+
+dotraplinkage void
+do_async_page_fault(struct pt_regs *regs, unsigned long error_code)
+{
+	enum ctx_state prev_state;
+
+	switch (kvm_read_and_reset_pf_reason()) {
+	default:
+		trace_do_page_fault(regs, error_code);
+		break;
+	case KVM_PV_REASON_PAGE_NOT_PRESENT:
+		/* page is swapped out by the host. */
+		prev_state = exception_enter();
+		exit_idle();
+		kvm_async_pf_task_wait((u32)read_cr2());
+		exception_exit(prev_state);
+		break;
+	case KVM_PV_REASON_PAGE_READY:
+		rcu_irq_enter();
+		exit_idle();
+		kvm_async_pf_task_wake((u32)read_cr2());
+		rcu_irq_exit();
+		break;
+	}
+}
+NOKPROBE_SYMBOL(do_async_page_fault);
+
+static void __init paravirt_ops_setup(void)
+{
+	pv_info.name = "KVM";
+
+	/*
+	 * KVM isn't paravirt in the sense of paravirt_enabled.  A KVM
+	 * guest kernel works like a bare metal kernel with additional
+	 * features, and paravirt_enabled is about features that are
+	 * missing.
+	 */
+	pv_info.paravirt_enabled = 0;
+
+	if (kvm_para_has_feature(KVM_FEATURE_NOP_IO_DELAY))
+		pv_cpu_ops.io_delay = kvm_io_delay;
+
+#ifdef CONFIG_X86_IO_APIC
+	no_timer_check = 1;
+#endif
+}
+
+static void kvm_register_steal_time(void)
+{
+	int cpu = smp_processor_id();
+	struct kvm_steal_time *st = &per_cpu(steal_time, cpu);
+
+	if (!has_steal_clock)
+		return;
+
+	memset(st, 0, sizeof(*st));
+
+	wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | KVM_MSR_ENABLED));
+	pr_info("kvm-stealtime: cpu %d, msr %llx\n",
+		cpu, (unsigned long long) slow_virt_to_phys(st));
+}
+
+static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED;
+
+static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
+{
+	/**
+	 * This relies on __test_and_clear_bit to modify the memory
+	 * in a way that is atomic with respect to the local CPU.
+	 * The hypervisor only accesses this memory from the local CPU so
+	 * there's no need for lock or memory barriers.
+	 * An optimization barrier is implied in apic write.
+	 */
+	if (__test_and_clear_bit(KVM_PV_EOI_BIT, this_cpu_ptr(&kvm_apic_eoi)))
+		return;
+	apic_write(APIC_EOI, APIC_EOI_ACK);
+}
+
+void kvm_guest_cpu_init(void)
+{
+	if (!kvm_para_available())
+		return;
+
+	if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF) && kvmapf) {
+		u64 pa = slow_virt_to_phys(this_cpu_ptr(&apf_reason));
+
+#ifdef CONFIG_PREEMPT
+		pa |= KVM_ASYNC_PF_SEND_ALWAYS;
+#endif
+		wrmsrl(MSR_KVM_ASYNC_PF_EN, pa | KVM_ASYNC_PF_ENABLED);
+		__this_cpu_write(apf_reason.enabled, 1);
+		printk(KERN_INFO"KVM setup async PF for cpu %d\n",
+		       smp_processor_id());
+	}
+
+	if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) {
+		unsigned long pa;
+		/* Size alignment is implied but just to make it explicit. */
+		BUILD_BUG_ON(__alignof__(kvm_apic_eoi) < 4);
+		__this_cpu_write(kvm_apic_eoi, 0);
+		pa = slow_virt_to_phys(this_cpu_ptr(&kvm_apic_eoi))
+			| KVM_MSR_ENABLED;
+		wrmsrl(MSR_KVM_PV_EOI_EN, pa);
+	}
+
+	if (has_steal_clock)
+		kvm_register_steal_time();
+}
+
+static void kvm_pv_disable_apf(void)
+{
+	if (!__this_cpu_read(apf_reason.enabled))
+		return;
+
+	wrmsrl(MSR_KVM_ASYNC_PF_EN, 0);
+	__this_cpu_write(apf_reason.enabled, 0);
+
+	printk(KERN_INFO"Unregister pv shared memory for cpu %d\n",
+	       smp_processor_id());
+}
+
+static void kvm_pv_guest_cpu_reboot(void *unused)
+{
+	/*
+	 * We disable PV EOI before we load a new kernel by kexec,
+	 * since MSR_KVM_PV_EOI_EN stores a pointer into old kernel's memory.
+	 * New kernel can re-enable when it boots.
+	 */
+	if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
+		wrmsrl(MSR_KVM_PV_EOI_EN, 0);
+	kvm_pv_disable_apf();
+	kvm_disable_steal_time();
+}
+
+static int kvm_pv_reboot_notify(struct notifier_block *nb,
+				unsigned long code, void *unused)
+{
+	if (code == SYS_RESTART)
+		on_each_cpu(kvm_pv_guest_cpu_reboot, NULL, 1);
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block kvm_pv_reboot_nb = {
+	.notifier_call = kvm_pv_reboot_notify,
+};
+
+static u64 kvm_steal_clock(int cpu)
+{
+	u64 steal;
+	struct kvm_steal_time *src;
+	int version;
+
+	src = &per_cpu(steal_time, cpu);
+	do {
+		version = src->version;
+		rmb();
+		steal = src->steal;
+		rmb();
+	} while ((version & 1) || (version != src->version));
+
+	return steal;
+}
+
+void kvm_disable_steal_time(void)
+{
+	if (!has_steal_clock)
+		return;
+
+	wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
+}
+
+#ifdef CONFIG_SMP
+static void __init kvm_smp_prepare_boot_cpu(void)
+{
+	kvm_guest_cpu_init();
+	native_smp_prepare_boot_cpu();
+	kvm_spinlock_init();
+}
+
+static void kvm_guest_cpu_online(void *dummy)
+{
+	kvm_guest_cpu_init();
+}
+
+static void kvm_guest_cpu_offline(void *dummy)
+{
+	kvm_disable_steal_time();
+	if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
+		wrmsrl(MSR_KVM_PV_EOI_EN, 0);
+	kvm_pv_disable_apf();
+	apf_task_wake_all();
+}
+
+static int kvm_cpu_notify(struct notifier_block *self, unsigned long action,
+			  void *hcpu)
+{
+	int cpu = (unsigned long)hcpu;
+	switch (action) {
+	case CPU_ONLINE:
+	case CPU_DOWN_FAILED:
+	case CPU_ONLINE_FROZEN:
+		smp_call_function_single(cpu, kvm_guest_cpu_online, NULL, 0);
+		break;
+	case CPU_DOWN_PREPARE:
+	case CPU_DOWN_PREPARE_FROZEN:
+		smp_call_function_single(cpu, kvm_guest_cpu_offline, NULL, 1);
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block kvm_cpu_notifier = {
+        .notifier_call  = kvm_cpu_notify,
+};
+#endif
+
+static void __init kvm_apf_trap_init(void)
+{
+	set_intr_gate(14, async_page_fault);
+}
+
+void __init kvm_guest_init(void)
+{
+	int i;
+
+	if (!kvm_para_available())
+		return;
+
+	paravirt_ops_setup();
+	register_reboot_notifier(&kvm_pv_reboot_nb);
+	for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++)
+		spin_lock_init(&async_pf_sleepers[i].lock);
+	if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF))
+		x86_init.irqs.trap_init = kvm_apf_trap_init;
+
+	if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
+		has_steal_clock = 1;
+		pv_time_ops.steal_clock = kvm_steal_clock;
+	}
+
+	if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
+		apic_set_eoi_write(kvm_guest_apic_eoi_write);
+
+	if (kvmclock_vsyscall)
+		kvm_setup_vsyscall_timeinfo();
+
+#ifdef CONFIG_SMP
+	smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
+	register_cpu_notifier(&kvm_cpu_notifier);
+#else
+	kvm_guest_cpu_init();
+#endif
+
+	/*
+	 * Hard lockup detection is enabled by default. Disable it, as guests
+	 * can get false positives too easily, for example if the host is
+	 * overcommitted.
+	 */
+	hardlockup_detector_disable();
+}
+
+static noinline uint32_t __kvm_cpuid_base(void)
+{
+	if (boot_cpu_data.cpuid_level < 0)
+		return 0;	/* So we don't blow up on old processors */
+
+	if (cpu_has_hypervisor)
+		return hypervisor_cpuid_base("KVMKVMKVM\0\0\0", 0);
+
+	return 0;
+}
+
+static inline uint32_t kvm_cpuid_base(void)
+{
+	static int kvm_cpuid_base = -1;
+
+	if (kvm_cpuid_base == -1)
+		kvm_cpuid_base = __kvm_cpuid_base();
+
+	return kvm_cpuid_base;
+}
+
+bool kvm_para_available(void)
+{
+	return kvm_cpuid_base() != 0;
+}
+EXPORT_SYMBOL_GPL(kvm_para_available);
+
+unsigned int kvm_arch_para_features(void)
+{
+	return cpuid_eax(kvm_cpuid_base() | KVM_CPUID_FEATURES);
+}
+
+static uint32_t __init kvm_detect(void)
+{
+	return kvm_cpuid_base();
+}
+
+const struct hypervisor_x86 x86_hyper_kvm __refconst = {
+	.name			= "KVM",
+	.detect			= kvm_detect,
+	.x2apic_available	= kvm_para_available,
+};
+EXPORT_SYMBOL_GPL(x86_hyper_kvm);
+
+static __init int activate_jump_labels(void)
+{
+	if (has_steal_clock) {
+		static_key_slow_inc(&paravirt_steal_enabled);
+		if (steal_acc)
+			static_key_slow_inc(&paravirt_steal_rq_enabled);
+	}
+
+	return 0;
+}
+arch_initcall(activate_jump_labels);
+
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+
+/* Kick a cpu by its apicid. Used to wake up a halted vcpu */
+static void kvm_kick_cpu(int cpu)
+{
+	int apicid;
+	unsigned long flags = 0;
+
+	apicid = per_cpu(x86_cpu_to_apicid, cpu);
+	kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid);
+}
+
+enum kvm_contention_stat {
+	TAKEN_SLOW,
+	TAKEN_SLOW_PICKUP,
+	RELEASED_SLOW,
+	RELEASED_SLOW_KICKED,
+	NR_CONTENTION_STATS
+};
+
+#ifdef CONFIG_KVM_DEBUG_FS
+#define HISTO_BUCKETS	30
+
+static struct kvm_spinlock_stats
+{
+	u32 contention_stats[NR_CONTENTION_STATS];
+	u32 histo_spin_blocked[HISTO_BUCKETS+1];
+	u64 time_blocked;
+} spinlock_stats;
+
+static u8 zero_stats;
+
+static inline void check_zero(void)
+{
+	u8 ret;
+	u8 old;
+
+	old = READ_ONCE(zero_stats);
+	if (unlikely(old)) {
+		ret = cmpxchg(&zero_stats, old, 0);
+		/* This ensures only one fellow resets the stat */
+		if (ret == old)
+			memset(&spinlock_stats, 0, sizeof(spinlock_stats));
+	}
+}
+
+static inline void add_stats(enum kvm_contention_stat var, u32 val)
+{
+	check_zero();
+	spinlock_stats.contention_stats[var] += val;
+}
+
+
+static inline u64 spin_time_start(void)
+{
+	return sched_clock();
+}
+
+static void __spin_time_accum(u64 delta, u32 *array)
+{
+	unsigned index;
+
+	index = ilog2(delta);
+	check_zero();
+
+	if (index < HISTO_BUCKETS)
+		array[index]++;
+	else
+		array[HISTO_BUCKETS]++;
+}
+
+static inline void spin_time_accum_blocked(u64 start)
+{
+	u32 delta;
+
+	delta = sched_clock() - start;
+	__spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
+	spinlock_stats.time_blocked += delta;
+}
+
+static struct dentry *d_spin_debug;
+static struct dentry *d_kvm_debug;
+
+struct dentry *kvm_init_debugfs(void)
+{
+	d_kvm_debug = debugfs_create_dir("kvm-guest", NULL);
+	if (!d_kvm_debug)
+		printk(KERN_WARNING "Could not create 'kvm' debugfs directory\n");
+
+	return d_kvm_debug;
+}
+
+static int __init kvm_spinlock_debugfs(void)
+{
+	struct dentry *d_kvm;
+
+	d_kvm = kvm_init_debugfs();
+	if (d_kvm == NULL)
+		return -ENOMEM;
+
+	d_spin_debug = debugfs_create_dir("spinlocks", d_kvm);
+
+	debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
+
+	debugfs_create_u32("taken_slow", 0444, d_spin_debug,
+		   &spinlock_stats.contention_stats[TAKEN_SLOW]);
+	debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
+		   &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
+
+	debugfs_create_u32("released_slow", 0444, d_spin_debug,
+		   &spinlock_stats.contention_stats[RELEASED_SLOW]);
+	debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
+		   &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
+
+	debugfs_create_u64("time_blocked", 0444, d_spin_debug,
+			   &spinlock_stats.time_blocked);
+
+	debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
+		     spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
+
+	return 0;
+}
+fs_initcall(kvm_spinlock_debugfs);
+#else  /* !CONFIG_KVM_DEBUG_FS */
+static inline void add_stats(enum kvm_contention_stat var, u32 val)
+{
+}
+
+static inline u64 spin_time_start(void)
+{
+	return 0;
+}
+
+static inline void spin_time_accum_blocked(u64 start)
+{
+}
+#endif  /* CONFIG_KVM_DEBUG_FS */
+
+struct kvm_lock_waiting {
+	struct arch_spinlock *lock;
+	__ticket_t want;
+};
+
+/* cpus 'waiting' on a spinlock to become available */
+static cpumask_t waiting_cpus;
+
+/* Track spinlock on which a cpu is waiting */
+static DEFINE_PER_CPU(struct kvm_lock_waiting, klock_waiting);
+
+__visible void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
+{
+	struct kvm_lock_waiting *w;
+	int cpu;
+	u64 start;
+	unsigned long flags;
+	__ticket_t head;
+
+	if (in_nmi())
+		return;
+
+	w = this_cpu_ptr(&klock_waiting);
+	cpu = smp_processor_id();
+	start = spin_time_start();
+
+	/*
+	 * Make sure an interrupt handler can't upset things in a
+	 * partially setup state.
+	 */
+	local_irq_save(flags);
+
+	/*
+	 * The ordering protocol on this is that the "lock" pointer
+	 * may only be set non-NULL if the "want" ticket is correct.
+	 * If we're updating "want", we must first clear "lock".
+	 */
+	w->lock = NULL;
+	smp_wmb();
+	w->want = want;
+	smp_wmb();
+	w->lock = lock;
+
+	add_stats(TAKEN_SLOW, 1);
+
+	/*
+	 * This uses set_bit, which is atomic but we should not rely on its
+	 * reordering gurantees. So barrier is needed after this call.
+	 */
+	cpumask_set_cpu(cpu, &waiting_cpus);
+
+	barrier();
+
+	/*
+	 * Mark entry to slowpath before doing the pickup test to make
+	 * sure we don't deadlock with an unlocker.
+	 */
+	__ticket_enter_slowpath(lock);
+
+	/* make sure enter_slowpath, which is atomic does not cross the read */
+	smp_mb__after_atomic();
+
+	/*
+	 * check again make sure it didn't become free while
+	 * we weren't looking.
+	 */
+	head = READ_ONCE(lock->tickets.head);
+	if (__tickets_equal(head, want)) {
+		add_stats(TAKEN_SLOW_PICKUP, 1);
+		goto out;
+	}
+
+	/*
+	 * halt until it's our turn and kicked. Note that we do safe halt
+	 * for irq enabled case to avoid hang when lock info is overwritten
+	 * in irq spinlock slowpath and no spurious interrupt occur to save us.
+	 */
+	if (arch_irqs_disabled_flags(flags))
+		halt();
+	else
+		safe_halt();
+
+out:
+	cpumask_clear_cpu(cpu, &waiting_cpus);
+	w->lock = NULL;
+	local_irq_restore(flags);
+	spin_time_accum_blocked(start);
+}
+PV_CALLEE_SAVE_REGS_THUNK(kvm_lock_spinning);
+
+/* Kick vcpu waiting on @lock->head to reach value @ticket */
+static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
+{
+	int cpu;
+
+	add_stats(RELEASED_SLOW, 1);
+	for_each_cpu(cpu, &waiting_cpus) {
+		const struct kvm_lock_waiting *w = &per_cpu(klock_waiting, cpu);
+		if (READ_ONCE(w->lock) == lock &&
+		    READ_ONCE(w->want) == ticket) {
+			add_stats(RELEASED_SLOW_KICKED, 1);
+			kvm_kick_cpu(cpu);
+			break;
+		}
+	}
+}
+
+/*
+ * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
+ */
+void __init kvm_spinlock_init(void)
+{
+	if (!kvm_para_available())
+		return;
+	/* Does host kernel support KVM_FEATURE_PV_UNHALT? */
+	if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
+		return;
+
+	pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
+	pv_lock_ops.unlock_kick = kvm_unlock_kick;
+}
+
+static __init int kvm_spinlock_init_jump(void)
+{
+	if (!kvm_para_available())
+		return 0;
+	if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
+		return 0;
+
+	static_key_slow_inc(&paravirt_ticketlocks_enabled);
+	printk(KERN_INFO "KVM setup paravirtual spinlock\n");
+
+	return 0;
+}
+early_initcall(kvm_spinlock_init_jump);
+
+#endif	/* CONFIG_PARAVIRT_SPINLOCKS */