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authorKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2010-10-18 10:49:10 -0400
committerKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2010-10-18 10:49:10 -0400
commit3a69e9165a271b026c7149886b96ab0cc2e9a36b (patch)
tree9a51f952039745feee23d21b3b6b3834aabeef0c
parent3b32f574a032bb5c93957317bd4ce5c3397d5a7b (diff)
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xen: Find an unbound irq number in reverse order (high to low).
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>
-rw-r--r--drivers/xen/events.c25
1 files changed, 20 insertions, 5 deletions
diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 1e39908d02f..bab5ac18fe0 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -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.
*/