libxl: choose an appropriate default for passthrough...

...if there is no IOMMU or it is globally disabled.

Without this patch, the following assertion may be hit:

xl: libxl_create.c:589: libxl__domain_make: Assertion `info->passthrough != LIBXL_PASSTHROUGH_UNKNOWN' failed.

This is because libxl__domain_create_info_setdefault() currently only sets
an appropriate value for 'passthrough' in the case that 'cap_hvm_directio'
is true, which is not the case unless an IOMMU is present and enabled in
the system. This is normally masked by xl choosing a default value, but
that will not happen if xl is not used (e.g. when using libvirt) or when
a stub domain is being created.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 5f2972bc03c12f1b4bfcca0dcc0f2f98129a60bb..62e13f3e7c8eeabcc4dc729290b7ea546b5badd4 100644 (file)
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -68,7 +68,11 @@ int libxl__domain_create_info_setdefault(libxl__gc *gc,
         c_info->passthrough = ((c_info->type == LIBXL_DOMAIN_TYPE_PV) ||
                                !info.cap_iommu_hap_pt_share) ?
             LIBXL_PASSTHROUGH_SYNC_PT : LIBXL_PASSTHROUGH_SHARE_PT;
-    }
+    } else if (!info.cap_hvm_directio)
+        c_info->passthrough = LIBXL_PASSTHROUGH_DISABLED;
+
+    /* An explicit setting should now have been chosen */
+    assert(c_info->passthrough != LIBXL_PASSTHROUGH_UNKNOWN);
 
     return 0;
 }