RE: [Xen-devel] [PATCH]: Really disable pirq's

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

Not sure if the change is a bit over-kill, since enable_pirq is has void
return type, while startup_pirq is "int" return type, with possibility
to fail.

For example, in following situation, the startup_pirq may fail : 1) when
startup_pirq again, fail to get free port, 2) if another domain try to
bind the pirq with BIND_PIRQ_WILL_SHARE cleared (like to probing, will
it happen?) between the shutdown_pirq/startup_pirq sequence.

-- Yunhong Jiang

xen-devel-bounces@xxxxxxxxxxxxxxxxxxx <> wrote:
> All,
>     I have a laptop here that has some interrupt trouble,
> unrelated to Xen (I
> believe it's a bug in the ACPI tables, but I digress).  On the
bare-metal
> kernel, if 999,900 out of 100,000 interrupts go
> un-acknowledged to a particular
> interrupt line, the kernel disables that interrupt line.  In
> the Xen kernel, the
> same logic applies.  However, when the Xen kernel goes to
> disable the physical
> interrupt, it only masks out the event channel:
> 
> static void disable_pirq(unsigned int irq)
> {
>        int evtchn = evtchn_from_irq(irq);
> 
>        if (VALID_EVTCHN(evtchn))
>                mask_evtchn(evtchn);
> }
> 
> And at this point, *all* interrupts on the affected machine
> seem to stop, not
> just this physical IRQ line.  I believe the problem is that
> when we go to
> disable a PIRQ, we actually need to get the HV to mask it out
> on the IOAPIC.
> This patch does exactly that; on disable_pirq(), we actually
> just call out to
> shutdown_pirq(), which ends up hypercalling and getting the HV
> to mask out the
> interrupt.  On the other side, I needed to modify
> enable_pirq() to call out to
> startup_pirq(), so that it would actually allocate the event channel.
> 
> With this patch in place, the affected laptop no longer hangs
> up when the kernel
> decides to disable that particular interrupt line.
> 
> Signed-off-by: Chris Lalancette <clalance@xxxxxxxxxx>

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