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."
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
drivers/xen/events.c | 13 ++++++++++---
1 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index e1bd0be..385734f 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -370,7 +370,11 @@ static int find_unbound_irq(void)
struct irq_desc *desc;
int start = get_nr_hw_irqs();
- for (irq = start; 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--) {
desc = irq_to_desc(irq);
/* only 0->15 have init'd desc; handle irq > 16 */
if (desc == NULL)
@@ -383,8 +387,8 @@ static int find_unbound_irq(void)
break;
}
- if (irq == nr_irqs)
- panic("No available IRQ to bind to: increase nr_irqs!\n");
+ if (irq == start)
+ goto no_irqs;
desc = irq_to_desc_alloc_node(irq, 0);
if (WARN_ON(desc == NULL))
@@ -393,6 +397,9 @@ static int find_unbound_irq(void)
dynamic_irq_init_keep_chip_data(irq);
return irq;
+
+no_irqs:
+ panic("No available IRQ to bind to: increase nr_irqs!\n");
}
static bool identity_mapped_irq(unsigned irq)
--
1.7.0.4
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