[PATCH 07/12] x86/io-apic: fix usage of setup_ioapic_dest()

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Attempt to clarify the purpose of setup_ioapic_dest(), as the comment ahead
of it is outdated, and looks to be a verbatim copy from Linux from one of
the code imports.

The function serves two purposes: shuffling the interrupts across CPUs
after SMP bringup or re-assigning all interrupts to CPU#0 if no IRQ
balancing is set at run time.  However the function won't perform any of
those functions correctly, as it was unconditionally using
desc->arch.cpu_mask as the target CPU mask for interrupts (which is the
current target anyway).

Fix by adding a new `shuffle` parameter that's used to signal whether the
function is intended to balance interrupts across CPUs, or to re-assign all
interrupts to the BSP.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
I couldn't find a specific Fixes tag to use here, I think this has been
broken all along.
---
 xen/arch/x86/include/asm/irq.h    |  2 +-
 xen/arch/x86/io_apic.c            | 13 +++++++------
 xen/arch/x86/platform_hypercall.c |  2 +-
 xen/arch/x86/smpboot.c            |  3 ++-
 4 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/include/asm/irq.h b/xen/arch/x86/include/asm/irq.h
index 7315150b66b4..df7b48c8653e 100644
--- a/xen/arch/x86/include/asm/irq.h
+++ b/xen/arch/x86/include/asm/irq.h
@@ -137,7 +137,7 @@ int i8259A_resume(void);
 void enable_IO_APIC(void);
 void setup_IO_APIC(void);
 void disable_IO_APIC(void);
-void setup_ioapic_dest(void);
+void setup_ioapic_dest(bool shuffle);
 vmask_t *io_apic_get_used_vector_map(unsigned int irq);
 
 extern unsigned int io_apic_irqs;
diff --git a/xen/arch/x86/io_apic.c b/xen/arch/x86/io_apic.c
index 3c59bf0e15da..19960d291c47 100644
--- a/xen/arch/x86/io_apic.c
+++ b/xen/arch/x86/io_apic.c
@@ -717,12 +717,14 @@ static int __init find_isa_irq_apic(int irq, int type)
 static int pin_2_irq(int idx, int apic, int pin);
 
 /*
- * This function currently is only a helper for the i386 smp boot process 
where 
- * we need to reprogram the ioredtbls to cater for the cpus which have come 
online
- * so mask in all cases should simply be TARGET_CPUS
+ * This function serves two different purposes: shuffling the IO-APIC
+ * interrupts across CPUs after SMP bringup, or re-assigning all interrupts to
+ * the BSP if IRQ balancing is disabled at runtime.  Such functional
+ * distinction is signaled by the `shuffle` parameter.
  */
-void /*__init*/ setup_ioapic_dest(void)
+void setup_ioapic_dest(bool shuffle)
 {
+    const cpumask_t *mask = shuffle ? TARGET_CPUS : cpumask_of(0);
     int pin, ioapic, irq, irq_entry;
 
     if (skip_ioapic_setup)
@@ -740,8 +742,7 @@ void /*__init*/ setup_ioapic_dest(void)
             desc = irq_to_desc(irq);
 
             spin_lock_irqsave(&desc->lock, flags);
-            BUG_ON(!cpumask_intersects(desc->arch.cpu_mask, &cpu_online_map));
-            set_ioapic_affinity_irq(desc, desc->arch.cpu_mask);
+            set_ioapic_affinity_irq(desc, mask);
             spin_unlock_irqrestore(&desc->lock, flags);
         }
     }
diff --git a/xen/arch/x86/platform_hypercall.c 
b/xen/arch/x86/platform_hypercall.c
index 79bb99e0b602..22fd65a6aa7e 100644
--- a/xen/arch/x86/platform_hypercall.c
+++ b/xen/arch/x86/platform_hypercall.c
@@ -337,7 +337,7 @@ ret_t do_platform_op(
         case QUIRK_NOIRQBALANCING:
             printk("Platform quirk -- Disabling IRQ balancing/affinity.\n");
             opt_noirqbalance = 1;
-            setup_ioapic_dest();
+            setup_ioapic_dest(false);
             break;
         case QUIRK_IOAPIC_BAD_REGSEL:
             dprintk(XENLOG_WARNING,
diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 69cc9bbc6e2c..55ea62d7d67f 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -1433,7 +1433,8 @@ void __init smp_cpus_done(void)
         check_nmi_watchdog();
     }
 
-    setup_ioapic_dest();
+    if ( !opt_noirqbalance )
+        setup_ioapic_dest(true);
 
     mtrr_save_state();
     mtrr_aps_sync_end();
-- 
2.51.0