From 3a69e9165a271b026c7149886b96ab0cc2e9a36b Mon Sep 17 00:00:00 2001 From: Konrad Rzeszutek Wilk Date: Mon, 18 Oct 2010 10:49:10 -0400 Subject: 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 Signed-off-by: Jeremy Fitzhardinge --- drivers/xen/events.c | 25 ++++++++++++++++++++----- 1 file changed, 20 insertions(+), 5 deletions(-) (limited to 'drivers/xen/events.c') diff --git a/drivers/xen/events.c b/drivers/xen/events.c index 1e39908d02f9..bab5ac18fe0e 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. */ -- cgit v1.2.3-55-g7522