[tip:x86/apic] iommu, x86: Avoid migrating VT-d posted interrupts

[tip-bot for Feng Wu <tipbot@zytor.com>]

Commit-ID:  d75f152fc389cdd73a6c17f1247fce9052fd579c
Gitweb:     http://git.kernel.org/tip/d75f152fc389cdd73a6c17f1247fce9052fd579c
Author:     Feng Wu <feng.wu@intel.com>
AuthorDate: Tue, 9 Jun 2015 13:20:33 +0800
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 12 Jun 2015 11:33:52 +0200

iommu, x86: Avoid migrating VT-d posted interrupts

When the interrupt is configured in posted mode, the destination of
the interrupt is set in the Posted-Interrupts Descriptor and the
migration of these interrupts happens during vCPU scheduling.

We still update the cached irte, which will be used when changing back
to remapping mode, but we avoid writing the table entry as this would
overwrite the posted mode entry.

Signed-off-by: Feng Wu <feng.wu@intel.com>
Reviewed-by: Jiang Liu <jiang.liu@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: David Woodhouse <David.Woodhouse@intel.com>
Acked-by: Joerg Roedel <joro@8bytes.org>
Cc: iommu@lists.linux-foundation.org
Cc: dwmw2@infradead.org
Link: http://lkml.kernel.org/r/1433827237-3382-7-git-send-email-feng.wu@intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 drivers/iommu/intel_irq_remapping.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel_irq_remapping.c b/drivers/iommu/intel_irq_remapping.c
index 68bce0a..3bcb459 100644
--- a/drivers/iommu/intel_irq_remapping.c
+++ b/drivers/iommu/intel_irq_remapping.c
@@ -1003,7 +1003,10 @@ intel_ir_set_affinity(struct irq_data *data, const struct cpumask *mask,
 	 */
 	irte->vector = cfg->vector;
 	irte->dest_id = IRTE_DEST(cfg->dest_apicid);
-	modify_irte(&ir_data->irq_2_iommu, irte);
+
+	/* Update the hardware only if the interrupt is in remapped mode. */
+	if (ir_data->irq_2_iommu.mode == IRQ_REMAPPING)
+		modify_irte(&ir_data->irq_2_iommu, irte);
 
 	/*
 	 * After this point, all the interrupts will start arriving