v4.19.13 snapshot.
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
new file mode 100644
index 0000000..717b484
--- /dev/null
+++ b/arch/x86/xen/spinlock.c
@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * 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 <linux/atomic.h>
+
+#include <asm/paravirt.h>
+#include <asm/qspinlock.h>
+
+#include <xen/interface/xen.h>
+#include <xen/events.h>
+
+#include "xen-ops.h"
+#include "debugfs.h"
+
+static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
+static DEFINE_PER_CPU(char *, irq_name);
+static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest);
+static bool xen_pvspin = true;
+
+static void xen_qlock_kick(int cpu)
+{
+ int irq = per_cpu(lock_kicker_irq, cpu);
+
+ /* Don't kick if the target's kicker interrupt is not initialized. */
+ if (irq == -1)
+ return;
+
+ xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
+}
+
+/*
+ * Halt the current CPU & release it back to the host
+ */
+static void xen_qlock_wait(u8 *byte, u8 val)
+{
+ int irq = __this_cpu_read(lock_kicker_irq);
+ atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest);
+
+ /* If kicker interrupts not initialized yet, just spin */
+ if (irq == -1 || in_nmi())
+ return;
+
+ /* Detect reentry. */
+ atomic_inc(nest_cnt);
+
+ /* If irq pending already and no nested call clear it. */
+ if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) {
+ xen_clear_irq_pending(irq);
+ } else if (READ_ONCE(*byte) == val) {
+ /* Block until irq becomes pending (or a spurious wakeup) */
+ xen_poll_irq(irq);
+ }
+
+ atomic_dec(nest_cnt);
+}
+
+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) {
+ if (cpu == 0)
+ static_branch_disable(&virt_spin_lock_key);
+ 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;
+}
+
+PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
+
+/*
+ * 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)
+{
+
+ /* Don't need to use pvqspinlock code if there is only 1 vCPU. */
+ if (num_possible_cpus() == 1)
+ xen_pvspin = false;
+
+ if (!xen_pvspin) {
+ printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
+ return;
+ }
+ printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
+
+ __pv_init_lock_hash();
+ pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
+ pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
+ pv_lock_ops.wait = xen_qlock_wait;
+ pv_lock_ops.kick = xen_qlock_kick;
+ pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
+}
+
+static __init int xen_parse_nopvspin(char *arg)
+{
+ xen_pvspin = false;
+ return 0;
+}
+early_param("xen_nopvspin", xen_parse_nopvspin);
+