Re: [Xen-devel] [PATCH v2] [Bugfix] x86/apic: Fix xen IRQ allocation failure caused by commit b81975eade8c

[David Vrabel <david.vrabel@citrix.com>]

On 12/01/15 13:39, Jiang Liu wrote:
> Commit b81975eade8c ("x86, irq: Clean up irqdomain transition code")
> breaks xen IRQ allocation because xen_smp_prepare_cpus() doesn't invoke
> setup_IO_APIC(), so no irqdomains created for IOAPICs and
> mp_map_pin_to_irq() fails at the very beginning.
> 
> Enhance xen_smp_prepare_cpus() to call setup_IO_APIC() to initialize
> irqdomain for IOAPICs.

Having Xen call setup_IO_APIC() to initialize the irq domains then having to
add special cases to it is just wrong.

The bits of init deferred by mp_register_apic() are also deferred to
two different places which looks odd.

What about something like the following (untested) patch?

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 3f5f604..e180680 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -253,8 +253,10 @@ int __init arch_early_ioapic_init(void)
 	if (!nr_legacy_irqs())
 		io_apic_irqs = ~0UL;
 
-	for_each_ioapic(i)
+	for_each_ioapic(i) {
+		BUG_ON(mp_irqdomain_create(ioapic));
 		alloc_ioapic_saved_registers(i);
+	}
 
 	/*
 	 * For legacy IRQ's, start with assigning irq0 to irq15 to
@@ -2379,8 +2381,6 @@ void __init setup_IO_APIC(void)
 	io_apic_irqs = nr_legacy_irqs() ? ~PIC_IRQS : ~0UL;
 
 	apic_printk(APIC_VERBOSE, "ENABLING IO-APIC IRQs\n");
-	for_each_ioapic(ioapic)
-		BUG_ON(mp_irqdomain_create(ioapic));
 
 	/*
          * Set up IO-APIC IRQ routing.
@@ -2929,7 +2929,8 @@ int mp_register_ioapic(int id, u32 address, u32 gsi_base,
 	/*
 	 * If mp_register_ioapic() is called during early boot stage when
 	 * walking ACPI/SFI/DT tables, it's too early to create irqdomain,
-	 * we are still using bootmem allocator. So delay it to setup_IO_APIC().
+	 * we are still using bootmem allocator. So delay it to
+	 * arch_early_ioapic_init().
 	 */
 	if (hotplug) {
 		if (mp_irqdomain_create(idx)) {

> --- a/arch/x86/kernel/apic/io_apic.c
> +++ b/arch/x86/kernel/apic/io_apic.c
> @@ -2369,6 +2381,15 @@ static void ioapic_destroy_irqdomain(int idx)
>  	ioapics[idx].pin_info = NULL;
>  }
>  
> +static void setup_IO_APIC_IDs(void)
> +{
> +	if (xen_domain())
> +		return;

This would have to xen_pv_domain().

David