Subject: Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable

From: Jeremy Fitzhardinge <[email-masked]>
Date: Tue, 20 Mar 2007 09:31:58 -0700

Linus Torvalds wrote:
> On Tue, 20 Mar 2007, Eric W. Biederman wrote:
>   
>> If that is the case.  In the normal kernel what would
>> the "the oops, we got an interrupt code do?"
>> I assume it would leave interrupts disabled when it returns?
>> Like we currently do with the delayed disable of normal interrupts?
>>     
>
> Yeah, disable interrupts, and set a flag that the fake "sti" can test, and 
> just return without doing anything.
>
> (You may or may not also need to do extra work to Ack the hardware 
> interrupt etc, which may be irq-controller specific. Once the CPU has 
> accepted the interrupt, you may not be able to just leave it dangling)
>   

So it would be something like:

    pda.intr_mask = 1;		/* disable interrupts */
    ...
    pda.intr_mask = 0;		/* enable interrupts */
    if (xchg(&pda.intr_pending, 0))	/* check pending */
    	asm("sti");		/* was pending; isr left cpu interrupts masked */

and in the interrupt handler:

    if (pda.intr_mask) {
    	pda.intr_pending = 1;
    	regs->eflags &= ~IF;
    	maybe_ack_interrupt_controller();
    	iret

    }

?

    J