libxl: disallow PCI device assignment for HVM guest when PoD is enabled

This replicates a Xend behavior, see ec78952374 ("xend: Dis-allow
device assignment if PoD is enabled.").

This change is restricted to HVM guest, as only HVM is relevant in the
counterpart in Xend. We're late in release cycle so the change should
only do what's necessary. Probably we can revisit it if we need to do
the same thing for PV guest in the future.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>

tools/libxl/libxl_create.c

@@ -707,6 +707,7 @@ static void initiate_domain_create(libxl__egc *egc,
     uint32_t domid;
     int i, ret;
     size_t last_devid = -1;
+    bool pod_enabled = false;
 
     /* convenience aliases */
     libxl_domain_config *const d_config = dcs->guest_config;
@@ -715,6 +716,25 @@ static void initiate_domain_create(libxl__egc *egc,
 
     domid = 0;
 
+    /* If target_memkb is smaller than max_memkb, the subsequent call
+     * to libxc when building HVM domain will enable PoD mode.
+     */
+    pod_enabled = (d_config->c_info.type == LIBXL_DOMAIN_TYPE_HVM) &&
+        (d_config->b_info.target_memkb < d_config->b_info.max_memkb);
+
+    /* We cannot have PoD and PCI device assignment at the same time
+     * for HVM guest. It was reported that IOMMU cannot work with PoD
+     * enabled because it needs to populated entire page table for
+     * guest. To stay on the safe side, we disable PCI device
+     * assignment when PoD is enabled.
+     */
+    if (d_config->c_info.type == LIBXL_DOMAIN_TYPE_HVM &&
+        d_config->num_pcidevs && pod_enabled) {
+        ret = ERROR_INVAL;
+        LOG(ERROR, "PCI device assignment for HVM guest failed due to PoD enabled");
+        goto error_out;
+    }
+
     ret = libxl__domain_create_info_setdefault(gc, &d_config->c_info);
     if (ret) goto error_out;