1 files changed, 353 insertions, 0 deletions
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
new file mode 100644
index 000000000..956374c1e
--- /dev/null
+++ b/arch/x86/xen/spinlock.c
@@ -0,0 +1,353 @@
+/*
+ * Split spinlock implementation out into its own file, so it can be
+ * compiled in a FTRACE-compatible way.
+ */
+#include <linux/kernel_stat.h>
+#include <linux/spinlock.h>
+#include <linux/debugfs.h>
+#include <linux/log2.h>
+#include <linux/gfp.h>
+#include <linux/slab.h>
+
+#include <asm/paravirt.h>
+
+#include <xen/interface/xen.h>
+#include <xen/events.h>
+
+#include "xen-ops.h"
+#include "debugfs.h"
+
+enum xen_contention_stat {
+	TAKEN_SLOW,
+	TAKEN_SLOW_PICKUP,
+	TAKEN_SLOW_SPURIOUS,
+	RELEASED_SLOW,
+	RELEASED_SLOW_KICKED,
+	NR_CONTENTION_STATS
+};
+
+
+#ifdef CONFIG_XEN_DEBUG_FS
+#define HISTO_BUCKETS	30
+static struct xen_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 = 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 xen_contention_stat var, u32 val)
+{
+	check_zero();
+	spinlock_stats.contention_stats[var] += val;
+}
+
+static inline u64 spin_time_start(void)
+{
+	return xen_clocksource_read();
+}
+
+static void __spin_time_accum(u64 delta, u32 *array)
+{
+	unsigned 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 = xen_clocksource_read() - start;
+
+	__spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
+	spinlock_stats.time_blocked += delta;
+}
+#else  /* !CONFIG_XEN_DEBUG_FS */
+static inline void add_stats(enum xen_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_XEN_DEBUG_FS */
+
+struct xen_lock_waiting {
+	struct arch_spinlock *lock;
+	__ticket_t want;
+};
+
+static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
+static DEFINE_PER_CPU(char *, irq_name);
+static DEFINE_PER_CPU(struct xen_lock_waiting, lock_waiting);
+static cpumask_t waiting_cpus;
+
+static bool xen_pvspin = true;
+__visible void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
+{
+	int irq = __this_cpu_read(lock_kicker_irq);
+	struct xen_lock_waiting *w = this_cpu_ptr(&lock_waiting);
+	int cpu = smp_processor_id();
+	u64 start;
+	__ticket_t head;
+	unsigned long flags;
+
+	/* If kicker interrupts not initialized yet, just spin */
+	if (irq == -1)
+		return;
+
+	start = spin_time_start();
+
+	/*
+	 * Make sure an interrupt handler can't upset things in a
+	 * partially setup state.
+	 */
+	local_irq_save(flags);
+	/*
+	 * We don't really care if we're overwriting some other
+	 * (lock,want) pair, as that would mean that we're currently
+	 * in an interrupt context, and the outer context had
+	 * interrupts enabled.  That has already kicked the VCPU out
+	 * of xen_poll_irq(), so it will just return spuriously and
+	 * retry with newly setup (lock,want).
+	 *
+	 * 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;
+
+	/* This uses set_bit, which atomic and therefore a barrier */
+	cpumask_set_cpu(cpu, &waiting_cpus);
+	add_stats(TAKEN_SLOW, 1);
+
+	/* clear pending */
+	xen_clear_irq_pending(irq);
+
+	/* Only check lock once pending cleared */
+	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;
+	}
+
+	/* Allow interrupts while blocked */
+	local_irq_restore(flags);
+
+	/*
+	 * If an interrupt happens here, it will leave the wakeup irq
+	 * pending, which will cause xen_poll_irq() to return
+	 * immediately.
+	 */
+
+	/* Block until irq becomes pending (or perhaps a spurious wakeup) */
+	xen_poll_irq(irq);
+	add_stats(TAKEN_SLOW_SPURIOUS, !xen_test_irq_pending(irq));
+
+	local_irq_save(flags);
+
+	kstat_incr_irq_this_cpu(irq);
+out:
+	cpumask_clear_cpu(cpu, &waiting_cpus);
+	w->lock = NULL;
+
+	local_irq_restore(flags);
+
+	spin_time_accum_blocked(start);
+}
+PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning);
+
+static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next)
+{
+	int cpu;
+
+	add_stats(RELEASED_SLOW, 1);
+
+	for_each_cpu(cpu, &waiting_cpus) {
+		const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu);
+
+		/* Make sure we read lock before want */
+		if (READ_ONCE(w->lock) == lock &&
+		    READ_ONCE(w->want) == next) {
+			add_stats(RELEASED_SLOW_KICKED, 1);
+			xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
+			break;
+		}
+	}
+}
+
+static irqreturn_t dummy_handler(int irq, void *dev_id)
+{
+	BUG();
+	return IRQ_HANDLED;
+}
+
+void xen_init_lock_cpu(int cpu)
+{
+	int irq;
+	char *name;
+
+	if (!xen_pvspin)
+		return;
+
+	WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
+	     cpu, per_cpu(lock_kicker_irq, cpu));
+
+	name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
+	irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
+				     cpu,
+				     dummy_handler,
+				     IRQF_PERCPU|IRQF_NOBALANCING,
+				     name,
+				     NULL);
+
+	if (irq >= 0) {
+		disable_irq(irq); /* make sure it's never delivered */
+		per_cpu(lock_kicker_irq, cpu) = irq;
+		per_cpu(irq_name, cpu) = name;
+	}
+
+	printk("cpu %d spinlock event irq %d\n", cpu, irq);
+}
+
+void xen_uninit_lock_cpu(int cpu)
+{
+	if (!xen_pvspin)
+		return;
+
+	unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
+	per_cpu(lock_kicker_irq, cpu) = -1;
+	kfree(per_cpu(irq_name, cpu));
+	per_cpu(irq_name, cpu) = NULL;
+}
+
+
+/*
+ * Our init of PV spinlocks is split in two init functions due to us
+ * using paravirt patching and jump labels patching and having to do
+ * all of this before SMP code is invoked.
+ *
+ * The paravirt patching needs to be done _before_ the alternative asm code
+ * is started, otherwise we would not patch the core kernel code.
+ */
+void __init xen_init_spinlocks(void)
+{
+
+	if (!xen_pvspin) {
+		printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
+		return;
+	}
+	printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
+	pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
+	pv_lock_ops.unlock_kick = xen_unlock_kick;
+}
+
+/*
+ * While the jump_label init code needs to happend _after_ the jump labels are
+ * enabled and before SMP is started. Hence we use pre-SMP initcall level
+ * init. We cannot do it in xen_init_spinlocks as that is done before
+ * jump labels are activated.
+ */
+static __init int xen_init_spinlocks_jump(void)
+{
+	if (!xen_pvspin)
+		return 0;
+
+	if (!xen_domain())
+		return 0;
+
+	static_key_slow_inc(&paravirt_ticketlocks_enabled);
+	return 0;
+}
+early_initcall(xen_init_spinlocks_jump);
+
+static __init int xen_parse_nopvspin(char *arg)
+{
+	xen_pvspin = false;
+	return 0;
+}
+early_param("xen_nopvspin", xen_parse_nopvspin);
+
+#ifdef CONFIG_XEN_DEBUG_FS
+
+static struct dentry *d_spin_debug;
+
+static int __init xen_spinlock_debugfs(void)
+{
+	struct dentry *d_xen = xen_init_debugfs();
+
+	if (d_xen == NULL)
+		return -ENOMEM;
+
+	if (!xen_pvspin)
+		return 0;
+
+	d_spin_debug = debugfs_create_dir("spinlocks", d_xen);
+
+	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("taken_slow_spurious", 0444, d_spin_debug,
+			   &spinlock_stats.contention_stats[TAKEN_SLOW_SPURIOUS]);
+
+	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(xen_spinlock_debugfs);
+
+#endif	/* CONFIG_XEN_DEBUG_FS */