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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 <>
Reviewed-by: Jiang Liu <>
Acked-by: David Woodhouse <>
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

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