[patch] x64: Avoid irq_chip mask/unmask in fixup_irqs for interrupt-remapping

[Suresh Siddha <suresh.b.siddha@intel.com>]

From: Suresh Siddha <suresh.b.siddha@intel.com>
Subject: x64: Avoid irq_chip mask/unmask in fixup_irqs for interrupt-remapping

In the presence of interrupt-remapping, irqs will be migrated in the
process context and we don't do (and there is no need to) irq_chip mask/unmask
while migrating the interrupt.

Similarly fix the fixup_irqs() that get called during cpu offline and avoid
calling irq_chip mask/unmask for irqs that are ok to be migrated in the
process context.

While we didn't observe any race condition with the existing code,
this change takes complete advantage of interrupt-remapping in
the newer generation platforms and avoids any potential HW lockup's
(that often worry Eric :)

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
---

diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
index 977d8b4..82265a5 100644
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -95,7 +95,7 @@ void fixup_irqs(void)
 			affinity = cpu_all_mask;
 		}
 
-		if (desc->chip->mask)
+		if (!(desc->status & IRQ_MOVE_PCNTXT) && desc->chip->mask)
 			desc->chip->mask(irq);
 
 		if (desc->chip->set_affinity)
@@ -103,7 +103,7 @@ void fixup_irqs(void)
 		else if (!(warned++))
 			set_affinity = 0;
 
-		if (desc->chip->unmask)
+		if (!(desc->status & IRQ_MOVE_PCNTXT) && desc->chip->unmask)
 			desc->chip->unmask(irq);
 
 		spin_unlock(&desc->lock);