[PATCH] x86_64 irq: Safely cleanup an irq after moving it.

The problem:  After moving an interrupt when is it safe to teardown
the data structures for receiving the interrupt at the old location?

With a normal pci device it is possible to issue a read to a device
to flush all posted writes.  This does not work for the oldest ioapics
because they are on a 3-wire apic bus which is a completely different
data path.  For some more modern ioapics when everything is using
front side bus delivery you can flush interrupts by simply issuing a
read to the ioapic.  For other modern ioapics emperical testing has
shown that this does not work.

So it appears the only reliable way to know the last of the irqs from an
ioapic have been received from before the ioapic was reprogrammed is to
received the first irq from the ioapic from after it was reprogrammed.

Once we know the last irq message has been received from an ioapic
into a local apic we then need to know that irq message has been
processed through the local apics.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/x86_64/kernel/i8259.c b/arch/x86_64/kernel/i8259.c
index 45d85630196a..21d95b747437 100644
--- a/arch/x86_64/kernel/i8259.c
+++ b/arch/x86_64/kernel/i8259.c
@@ -450,6 +450,7 @@ void spurious_interrupt(void);
 void error_interrupt(void);
 void reschedule_interrupt(void);
 void call_function_interrupt(void);
+void irq_move_cleanup_interrupt(void);
 void invalidate_interrupt0(void);
 void invalidate_interrupt1(void);
 void invalidate_interrupt2(void);
@@ -537,7 +538,10 @@ void __init init_IRQ(void)
 
         /* IPI for generic function call */
         set_intr_gate(CALL_FUNCTION_VECTOR, call_function_interrupt);
-#endif  
+
+        /* Low priority IPI to cleanup after moving an irq */
+        set_intr_gate(IRQ_MOVE_CLEANUP_VECTOR, irq_move_cleanup_interrupt);
+#endif
         set_intr_gate(THERMAL_APIC_VECTOR, thermal_interrupt);
         set_intr_gate(THRESHOLD_APIC_VECTOR, threshold_interrupt);