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xen: Find an unbound irq number in reverse order (high to low).

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In earlier Xen Linux kernels, the IRQ mapping was a straight 1:1 and the
find_unbound_irq started looking around 256 for open IRQs and up. IRQs
from 0 to 255 were reserved for PCI devices.  Previous to this patch,
the 'find_unbound_irq'  started looking at get_nr_hw_irqs() number.
For privileged  domain where the ACPI information is available that
returns the upper-bound of what the GSIs. For non-privileged PV domains,
where ACPI is no-existent the get_nr_hw_irqs() reports the IRQ_LEGACY (16).
With PCI passthrough enabled, and with PCI cards that have IRQs pinned
to a higher number than 16 we collide with previously allocated IRQs.
Specifically the PCI IRQs collide with the IPI's for Xen functions
(as they are allocated earlier).
For example:

00:00.11 USB Controller: ATI Technologies Inc SB700 USB OHCI1 Controller (prog-if 10 [OHCI])
	...
	Interrupt: pin A routed to IRQ 18

[root@localhost ~]# cat /proc/interrupts | head
           CPU0       CPU1       CPU2
 16:      38186          0          0   xen-dyn-virq      timer0
 17:        149          0          0   xen-dyn-ipi       spinlock0
 18:        962          0          0   xen-dyn-ipi       resched0

and when the USB controller is loaded, the kernel reports:
IRQ handler type mismatch for IRQ 18
current handler: resched0

One way to fix this is to reverse the logic when looking for un-used
IRQ numbers and start with the highest available number. With that,
we would get:

           CPU0       CPU1       CPU2
... snip ..
292:         35          0          0   xen-dyn-ipi       callfunc0
293:       3992          0          0   xen-dyn-ipi       resched0
294:        224          0          0   xen-dyn-ipi       spinlock0
295:      57183          0          0   xen-dyn-virq      timer0
NMI:          0          0          0   Non-maskable interrupts
.. snip ..

And interrupts for PCI cards are now accessible.

This patch also includes the fix, found by Ian Campbell, titled
"xen: fix off-by-one error in find_unbound_irq."

[v2: Added an explanation in the code]
[v3: Rebased on top of tip/irq/core]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
This commit is contained in:
Konrad Rzeszutek Wilk 2010-10-18 10:49:10 -04:00
parent 3b32f574a0
commit 3a69e9165a
1 changed files with 20 additions and 5 deletions
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25
drivers/xen/events.c
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@ -368,8 +368,13 @@ static int find_unbound_irq(void)
{
struct irq_data *data;
int irq, res;
int start = get_nr_hw_irqs();
for (irq = 0; irq < nr_irqs; irq++) {
if (start == nr_irqs)
goto no_irqs;
/* nr_irqs is a magic value. Must not use it.*/
for (irq = nr_irqs-1; irq > start; irq--) {
data = irq_get_irq_data(irq);
/* only 0->15 have init'd desc; handle irq > 16 */
if (!data)
@ -382,8 +387,8 @@ static int find_unbound_irq(void)
return irq;
}
if (irq == nr_irqs)
panic("No available IRQ to bind to: increase nr_irqs!\n");
if (irq == start)
goto no_irqs;
res = irq_alloc_desc_at(irq, 0);
@ -391,6 +396,9 @@ static int find_unbound_irq(void)
return -1;
return irq;
no_irqs:
panic("No available IRQ to bind to: increase nr_irqs!\n");
}
static bool identity_mapped_irq(unsigned irq)
@ -544,8 +552,15 @@ static int find_irq_by_gsi(unsigned gsi)
return -1;
}
/*
* Allocate a physical irq, along with a vector. We don't assign an
/* xen_allocate_irq might allocate irqs from the top down, as a
* consequence don't assume that the irq number returned has a low value
* or can be used as a pirq number unless you know otherwise.
*
* One notable exception is when xen_allocate_irq is called passing an
* hardware gsi as argument, in that case the irq number returned
* matches the gsi number passed as first argument.
* Note: We don't assign an
* event channel until the irq actually started up. Return an
* existing irq if we've already got one for the gsi.
*/