vt-d: ensure x2apic is not enabled accidently if no DRHD at all.

Thanks to Jan Beulich for pointing this out.

Signed-off-by: Dexuan Cui <dexuan.cui@intel.com>

diff --git a/xen/drivers/passthrough/vtd/intremap.c b/xen/drivers/passthrough/vtd/intremap.c
index 87c639d50159546c519c6e7fbbbcc8b25d93ad63..9459a81736ed7f290ca0fe82364baf84b065a1c9 100644 (file)
--- a/xen/drivers/passthrough/vtd/intremap.c
+++ b/xen/drivers/passthrough/vtd/intremap.c
@@ -131,6 +131,9 @@ int iommu_supports_eim(void)
     if ( !iommu_enabled || !iommu_qinval || !iommu_intremap )
         return 0;
 
+    if ( list_empty(&acpi_drhd_units) )
+        return 0;
+
     for_each_drhd_unit ( drhd )
         if ( !ecap_queued_inval(drhd->ecap) ||
              !ecap_intr_remap(drhd->ecap) ||