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

Jeremy Fitzhardinge
2007-03-20T16:32:06Z

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