linux-kernel - [v9 5/9] iommu, x86: No need to migrating irq for VT-d Posted-Interrupts

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Message-Id: <1433482974-14614-6-git-send-email-feng.wu@intel.com>
Date:	Fri,  5 Jun 2015 13:42:50 +0800
From:	Feng Wu <feng.wu@...el.com>
To:	joro@...tes.org, dwmw2@...radead.org, tglx@...utronix.de
Cc:	jiang.liu@...ux.intel.com, iommu@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, Feng Wu <feng.wu@...el.com>
Subject: [v9 5/9] iommu, x86: No need to migrating irq for VT-d Posted-Interrupts

We don't need to migrate the irqs for VT-d Posted-Interrupts here.
When 'pst' is set in IRTE, the associated irq will be posted to
guests instead of interrupt remapping. The destination of the
interrupt is set in Posted-Interrupts Descriptor, and the migration
happens during vCPU scheduling.

However, we still update the cached irte here, which can be used
when changing back to remapping mode.

Signed-off-by: Feng Wu <feng.wu@...el.com>
Reviewed-by: Jiang Liu <jiang.liu@...ux.intel.com>
Acked-by: David Woodhouse <David.Woodhouse@...el.com>
---
 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 028d628..c30845a 100644
--- a/drivers/iommu/intel_irq_remapping.c
+++ b/drivers/iommu/intel_irq_remapping.c
@@ -1002,7 +1002,10 @@ 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
-- 
2.1.0

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