text: // 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 <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 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);
  
  	/* If kicker interrupts not initialized yet, just spin */
  	if (irq == -1)
  		return;
  
  	/* clear pending */
  	xen_clear_irq_pending(irq);
  	barrier();
  
  	/*
  	 * We check the byte value after clearing pending IRQ to make sure
  	 * that we won't miss a wakeup event because of the clearing.
  	 *
  	 * The sync_clear_bit() call in xen_clear_irq_pending() is atomic.
  	 * So it is effectively a memory barrier for x86.
  	 */
  	if (READ_ONCE(*byte) != val)
  		return;
  
  	/*
  	 * 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);
  }
  
  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)
  {
  
  	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);
  
  