Xen Guest中断简介

Xen Guest中断简介(转载注明出处，所有内容均为Superymk原创，版权归作者所有)

• 在Xen 3.4.2中，Xen Guest中断包括硬件中断和软中断（Soft IRQ）两种，在硬件虚拟化中，前者的分发在陷入Xen Hypervisor后由其负责，后者的话其实是在调用Xen Hypervisor中的一些函数，只能算模拟
• 与前者功能相关的文件是arch\x86\vmx\Vmx.c文件中的vmx_vmexit_handler函数，后者则是arch\x86\irq.c 文件的do_IRQ函数，翻翻就可以看到，在xen中，Timer Interrupt和UART的一些中断都是软件中断。

Xen Guest中断拦截试验

• 在做context switch相关的实验中要注意，对于中断，既要处理外部中断又要处理异常，其效果也就是整个idt表都要hook住。
• 附上一些代码关键point

在vmx_vmexit_handler函数中

 switch ( exit_reason )
    {
    case EXIT_REASON_EXCEPTION_NMI:
    {
        /*
         * We don't set the software-interrupt exiting (INT n).
         * (1) We can get an exception (e.g. #PG) in the guest, or
         * (2) NMI
         */
        unsigned int intr_info, vector;

        intr_info = __vmread(VM_EXIT_INTR_INFO);
        BUG_ON(!(intr_info & INTR_INFO_VALID_MASK));

        vector = intr_info & INTR_INFO_VECTOR_MASK;

		//[Superymk] Add hook_idt //<---------------------------Key Point
		if(hook_idt)
		{
			joan_dprintk("Int:%d\n", vector);
		}
		//[Superymk] Add finished
        /*
         * Re-set the NMI shadow if vmexit caused by a guest IRET fault (see 3B
         * 25.7.1.2, "Resuming Guest Software after Handling an Exception").
         * (NB. If we emulate this IRET for any reason, we should re-clear!)
         */

在do_IRQ函数中

 spin_lock(&desc->lock);
    desc->handler->ack(vector);

    if ( likely(desc->status & IRQ_GUEST) )
    {       
　　　　 //[Superymk] Add hook_idt //<---------------------------Key Point
	if(hook_idt)
	{
		joan_dprintk("Int:%d\n", vector);
	}
	//[Superymk] Add finished
        irq_enter();
        __do_IRQ_guest(vector);
        irq_exit();
        spin_unlock(&desc->lock);
        return;
    }

    desc->status &= ~IRQ_REPLAY;
    desc->status |= IRQ_PENDING;

    /*
     * Since we set PENDING, if another processor is handling a different 
     * instance of this same irq, the other processor will take care of it.
     */
    if ( desc->status & (IRQ_DISABLED | IRQ_INPROGRESS) )
        goto out;

    desc->status |= IRQ_INPROGRESS;

    action = desc->action;
    while ( desc->status & IRQ_PENDING )
    {
 　　　　//[Superymk] Add hook_idt //<---------------------------Key Point
	if(hook_idt)
	{
		joan_dprintk("Int:%d\n", vector);
	}
	//[Superymk] Add finished
        desc->status &= ~IRQ_PENDING;  
        irq_enter();
        spin_unlock_irq(&desc->lock);
        action->handler(vector_to_irq(vector), action->dev_id, regs);
        spin_lock_irq(&desc->lock);
        irq_exit();
    }

• 之所以都在irq_enter()外修改，是因为尽量缩短IRQ的处理时间。（它们需要在高特权级别下运行，未核实irq_enter()是否会提升IRQL）