vtd/iommu: permit group devices to passthrough in relaxed mode

Currently we don't allow passing through any group devices which are
sharing same RMRR entry since it would break security among VMs. And
indeed, we expect we can figure out a better way to handle this kind
of case completely.

But before the group assignment gets implemented, we might make this
permission dependent on our RMRR policy. So, now it would be allowed
in the relaxed mode.

Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>

xen/drivers/passthrough/vtd/iommu.c

@@ -2297,7 +2297,9 @@ static int intel_iommu_assign_device(
     /*
      * In rare cases one given rmrr is shared by multiple devices but
      * obviously this would put the security of a system at risk. So
-     * we should prevent from this sort of device assignment.
+     * we would prevent from this sort of device assignment. But this
+     * can be permitted if user set
+     *      "pci = [ 'sbdf, rdm_policy=relaxed' ]"
      *
      * TODO: in the future we can introduce group device assignment
      * interface to make sure devices sharing RMRR are assigned to the
@@ -2310,12 +2312,16 @@ static int intel_iommu_assign_device(
              PCI_DEVFN2(bdf) == devfn &&
              rmrr->scope.devices_cnt > 1 )
         {
-            printk(XENLOG_G_ERR VTDPREFIX
-                   " cannot assign %04x:%02x:%02x.%u"
+            bool_t relaxed = !!(flag & XEN_DOMCTL_DEV_RDM_RELAXED);
+
+            printk(XENLOG_G_WARNING VTDPREFIX
+                   " It's %s to assign %04x:%02x:%02x.%u"
                    " with shared RMRR at %"PRIx64" for Dom%d.\n",
+                   relaxed ? "risky" : "disallowed",
                    seg, bus, PCI_SLOT(devfn), PCI_FUNC(devfn),
                    rmrr->base_address, d->domain_id);
-            return -EPERM;
+            if ( !relaxed )
+                return -EPERM;
         }
     }