#include <linux/hardirq.h>
  
  #include <asm/x86_init.h>
  
  #include <xen/interface/xen.h>
  #include <xen/interface/sched.h>
  #include <xen/interface/vcpu.h>
  #include <xen/features.h>
  #include <xen/events.h>
  
  #include <asm/xen/hypercall.h>
  #include <asm/xen/hypervisor.h>
  
  #include "xen-ops.h"
  
  /*
   * Force a proper event-channel callback from Xen after clearing the
   * callback mask. We do this in a very simple manner, by making a call
   * down into Xen. The pending flag will be checked by Xen on return.
   */
  void xen_force_evtchn_callback(void)
  {
  	(void)HYPERVISOR_xen_version(0, NULL);
  }
  
  asmlinkage unsigned long xen_save_fl(void)
  {
  	struct vcpu_info *vcpu;
  	unsigned long flags;
  
  	vcpu = this_cpu_read(xen_vcpu);
  
  	/* flag has opposite sense of mask */
  	flags = !vcpu->evtchn_upcall_mask;
  
  	/* convert to IF type flag
  	   -0 -> 0x00000000
  	   -1 -> 0xffffffff
  	*/
  	return (-flags) & X86_EFLAGS_IF;
  }
  PV_CALLEE_SAVE_REGS_THUNK(xen_save_fl);
  
  __visible void xen_restore_fl(unsigned long flags)
  {
  	struct vcpu_info *vcpu;
  
  	/* convert from IF type flag */
  	flags = !(flags & X86_EFLAGS_IF);
  
  	/* See xen_irq_enable() for why preemption must be disabled. */
  	preempt_disable();
  	vcpu = this_cpu_read(xen_vcpu);
  	vcpu->evtchn_upcall_mask = flags;
  
  	if (flags == 0) {
  		barrier(); /* unmask then check (avoid races) */
  		if (unlikely(vcpu->evtchn_upcall_pending))
  			xen_force_evtchn_callback();
  		preempt_enable();
  	} else
  		preempt_enable_no_resched();
  }
  PV_CALLEE_SAVE_REGS_THUNK(xen_restore_fl);
  
  asmlinkage void xen_irq_disable(void)
  {
  	/* There's a one instruction preempt window here.  We need to
  	   make sure we're don't switch CPUs between getting the vcpu
  	   pointer and updating the mask. */
  	preempt_disable();
  	this_cpu_read(xen_vcpu)->evtchn_upcall_mask = 1;
  	preempt_enable_no_resched();
  }
  PV_CALLEE_SAVE_REGS_THUNK(xen_irq_disable);
  
  asmlinkage void xen_irq_enable(void)
  {
  	struct vcpu_info *vcpu;
  
  	/*
  	 * We may be preempted as soon as vcpu->evtchn_upcall_mask is
  	 * cleared, so disable preemption to ensure we check for
  	 * events on the VCPU we are still running on.
  	 */
  	preempt_disable();
  
  	vcpu = this_cpu_read(xen_vcpu);
  	vcpu->evtchn_upcall_mask = 0;
  
  	/* Doesn't matter if we get preempted here, because any
  	   pending event will get dealt with anyway. */
  
  	barrier(); /* unmask then check (avoid races) */
  	if (unlikely(vcpu->evtchn_upcall_pending))
  		xen_force_evtchn_callback();
  
  	preempt_enable();
  }
  PV_CALLEE_SAVE_REGS_THUNK(xen_irq_enable);
  
  static void xen_safe_halt(void)
  {
  	/* Blocking includes an implicit local_irq_enable(). */
  	if (HYPERVISOR_sched_op(SCHEDOP_block, NULL) != 0)
  		BUG();
  }
  
  static void xen_halt(void)
  {
  	if (irqs_disabled())
  		HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL);
  	else
  		xen_safe_halt();
  }
  
  static const struct pv_irq_ops xen_irq_ops __initconst = {
  	.save_fl = PV_CALLEE_SAVE(xen_save_fl),
  	.restore_fl = PV_CALLEE_SAVE(xen_restore_fl),
  	.irq_disable = PV_CALLEE_SAVE(xen_irq_disable),
  	.irq_enable = PV_CALLEE_SAVE(xen_irq_enable),
  
  	.safe_halt = xen_safe_halt,
  	.halt = xen_halt,
  #ifdef CONFIG_X86_64
  	.adjust_exception_frame = xen_adjust_exception_frame,
  #endif
  };
  
  void __init xen_init_irq_ops(void)
  {
  	/* For PVH we use default pv_irq_ops settings. */
  	if (!xen_feature(XENFEAT_hvm_callback_vector))
  		pv_irq_ops = xen_irq_ops;
  	x86_init.irqs.intr_init = xen_init_IRQ;
  }