libxl: Use vkb=[] for HVMs

xl/libxl only applies vkb=[] to PV & PVH guests.  HVM gets only a single
vkb by default, but that can be disabled by the vkb_device boolean.
Notably the HVM vkb cannot be configured, so feature-abs-pointer or the
backend-type cannot be specified.

Re-arrange the logic so that vkb=[] is handled regardless of domain
type.  If vkb is empty or unspecified, follow the vkb_device boolean for
HVMs.  Nothing changes for PVH & PV.  HVMs can now get a configured vkb
instead of just the default one.

The chance for regression is an HVM config with
vkb=["$something"]
vkb_device=false

Which would now get a vkb.

This is useful for vGlass which provides a VKB to HVMs.  vGlass wants to
specify feature-abs-pointer, but that is racily written by vGlass
instead of coming through the xl.cfg.  Unhelpfully, Linux xen-kbdfront
reads the backend nodes without checking that the backend is in
InitWait.

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>

CHANGELOG.md

@@ -13,6 +13,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
  - On x86:
    - HVM PIRQs are disabled by default.
    - Reduce IOMMU setup time for hardware domain.
+ - xl/libxl configures vkb=[] for HVM domains with priority over vkb_device.
 
 ### Added
  - On x86:

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

@@ -2710,6 +2710,8 @@ device.
 
 Specifies that the HVM guest gets a vkdb. The default is true (1).
 
+This option is only used when B<vkb=[]> is unset.
+
 =item B<usb=BOOLEAN>
 
 Enables or disables an emulated USB bus in the guest.

tools/libs/light/libxl_create.c

@@ -1769,24 +1769,32 @@ static void domcreate_launch_dm(libxl__egc *egc, libxl__multidev *multidev,
         libxl__device_add(gc, domid, &libxl__virtio_devtype,
                           &d_config->virtios[i]);
 
+    if (d_config->num_vkbs) {
+        for (i = 0; i < d_config->num_vkbs; i++) {
+            ret = libxl__device_add(gc, domid, &libxl__vkb_devtype,
+                                    &d_config->vkbs[i]);
+            if (ret) goto error_out;
+        }
+    } else if (d_config->c_info.type == LIBXL_DOMAIN_TYPE_HVM &&
+               libxl_defbool_val(d_config->b_info.u.hvm.vkb_device)) {
+        libxl_device_vkb vkb;
+
+        libxl_device_vkb_init(&vkb);
+        libxl__device_add(gc, domid, &libxl__vkb_devtype, &vkb);
+        libxl_device_vkb_dispose(&vkb);
+    }
+
     switch (d_config->c_info.type) {
     case LIBXL_DOMAIN_TYPE_HVM:
     {
         libxl__device_console console;
         libxl__device device;
-        libxl_device_vkb vkb;
 
         init_console_info(gc, &console, 0);
         console.backend_domid = state->console_domid;
         libxl__device_console_add(gc, domid, &console, state, &device);
         libxl__device_console_dispose(&console);
 
-        if (libxl_defbool_val(d_config->b_info.u.hvm.vkb_device)) {
-            libxl_device_vkb_init(&vkb);
-            libxl__device_add(gc, domid, &libxl__vkb_devtype, &vkb);
-            libxl_device_vkb_dispose(&vkb);
-        }
-
         dcs->sdss.dm.guest_domid = domid;
         if (libxl_defbool_val(d_config->b_info.device_model_stubdomain))
             libxl__spawn_stub_dm(egc, &dcs->sdss);
@@ -1814,11 +1822,6 @@ static void domcreate_launch_dm(libxl__egc *egc, libxl__multidev *multidev,
                               &d_config->vfbs[i]);
         }
 
-        for (i = 0; i < d_config->num_vkbs; i++) {
-            libxl__device_add(gc, domid, &libxl__vkb_devtype,
-                              &d_config->vkbs[i]);
-        }
-
         if (d_config->b_info.arch_arm.vuart == LIBXL_VUART_TYPE_SBSA_UART) {
             init_console_info(gc, &vuart, 0);
             vuart.backend_domid = state->console_domid;