VT-d: posted interrupts require interrupt remapping

Initially I had just noticed the unnecessary indirection in the call
from pi_update_irte(). The generic wrapper having an iommu_intremap
conditional made me look at the setup code though. So first of all
enforce the necessary dependency.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 6c54663786
master date: 2019-04-09 15:12:07 +0200

xen/drivers/passthrough/vtd/intremap.c

@@ -988,7 +988,8 @@ int pi_update_irte(const struct pi_desc *pi_desc, const struct pirq *pirq,
     spin_unlock_irq(&desc->lock);
 
     ASSERT(pcidevs_locked());
-    return iommu_update_ire_from_msi(msi_desc, &msi_desc->msg);
+
+    return msi_msg_write_remap_rte(msi_desc, &msi_desc->msg);
 
  unlock_out:
     spin_unlock_irq(&desc->lock);

xen/drivers/passthrough/vtd/iommu.c

@@ -2342,7 +2342,7 @@ int __init intel_vtd_setup(void)
          * not supported, since we count on this feature to
          * atomically update 16-byte IRTE in posted format.
          */
-        if ( !cap_intr_post(iommu->cap) || !cpu_has_cx16 )
+        if ( !cap_intr_post(iommu->cap) || !iommu_intremap || !cpu_has_cx16 )
             iommu_intpost = 0;
 
         if ( !vtd_ept_page_compatible(iommu) )