xl: pvshim: Provide and document xl config

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
Signed-off-by: Wei Liu <wei.liu2@citrix.com>

docs/man/xl.cfg.pod.5.in

@@ -508,6 +508,41 @@ Load the specified file as firmware for the guest.
 Currently there's no firmware available for PVH guests, they should be
 booted using the B<Direct Kernel Boot> method or the B<bootloader> option.
 
+=over 4
+
+=item B<pvshim=BOOLEAN>
+
+Whether to boot this guest as a PV guest within a PVH container.
+Ie, the guest will experience a PV environment,
+but
+processor hardware extensions are used to
+separate its address space
+to mitigate the Meltdown attack (CVE-2017-5754).
+
+Default is false.
+
+=item B<pvshim_path="PATH">
+
+The PV shim is a specially-built firmware-like executable
+constructed from the hypervisor source tree.
+This option specifies to use a non-default shim.
+Ignored if pvhsim is false.
+
+=item B<pvshim_cmdline="STRING">
+
+Command line for the shim.
+Default is "pv-shim console=xen,pv sched=null".
+Ignored if pvhsim is false.
+
+=item B<pvshim_extra="STRING">
+
+Extra command line arguments for the shim.
+If supplied, appended to the value for pvshim_cmdline.
+Default is empty.
+Ignored if pvhsim is false.
+
+=back
+
 =head3 Other Options
 
 =over 4

tools/xl/xl_parse.c

@@ -964,6 +964,20 @@ void parse_config_data(const char *config_source,
         xlu_cfg_replace_string(config, "pool", &c_info->pool_name, 0);
 
     libxl_domain_build_info_init_type(b_info, c_info->type);
+
+    if (b_info->type == LIBXL_DOMAIN_TYPE_PVH) {
+        xlu_cfg_get_defbool(config, "pvshim", &b_info->u.pvh.pvshim, 0);
+        if (!xlu_cfg_get_string(config, "pvshim_path", &buf, 0))
+            xlu_cfg_replace_string(config, "pvshim_path",
+                                   &b_info->u.pvh.pvshim_path, 0);
+        if (!xlu_cfg_get_string(config, "pvshim_cmdline", &buf, 0))
+            xlu_cfg_replace_string(config, "pvshim_cmdline",
+                                   &b_info->u.pvh.pvshim_cmdline, 0);
+        if (!xlu_cfg_get_string(config, "pvshim_extra", &buf, 0))
+            xlu_cfg_replace_string(config, "pvshim_extra",
+                                   &b_info->u.pvh.pvshim_extra, 0);
+    }
+
     if (blkdev_start)
         b_info->blkdev_start = strdup(blkdev_start);