From e4cf85bd3ad44aed28cf3e8d3bfd67fec38ebdab Mon Sep 17 00:00:00 2001

From: Laszlo Ersek <lersek@redhat.com>

Date: Thu, 6 Jan 2022 15:09:05 +0100

Subject: [PATCH] output/create_libvirt_xml: pick "virtio-transitional" models

 when needed

In the domain XML we generate, we do not assign PCI B/D/F addresses to

devices; that job is left to libvirtd. When using the Q35 machine type,

libvirtd places the virtio devices into PCI Express Root Ports. As a

consequence, QEMU disables virtio-0.9.5 support on these devices, and so

guest OSes without virtio-1.0 drivers cannot drive them.

Prevent QEMU from turning off the virtio-0.9.5 ("legacy") protocol by

specifying the "virtio-transitional" (not "virtio") model for our virtio

devices:

- For non-disk devices, simply change the value of the existent "model"

  attribute.

- For disk devices, add the "model" attribute as a new one.

(In fact, libvirtd doesn't (only) add the "disable_legacy=off" QEMU device

property for the "virtio-transitional" devices -- libvirtd even moves

these devices from PCI Express Root Ports to a dedicated

"pcie-to-pci-bridge". This has the same effect on QEMU.)

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1942325

Signed-off-by: Laszlo Ersek <lersek@redhat.com>

Message-Id: <20220106140910.13695-5-lersek@redhat.com>

Acked-by: Richard W.M. Jones <rjones@redhat.com>

---

 output/create_libvirt_xml.ml | 28 ++++++++++++++++++----------

 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/output/create_libvirt_xml.ml b/output/create_libvirt_xml.ml

index 9413cc0b..87bfab17 100644

--- a/output/create_libvirt_xml.ml

+++ b/output/create_libvirt_xml.ml

@@ -312,18 +312,26 @@ let create_libvirt_xml ?pool source inspect

   (* The devices. *)

   let devices = ref [] in

+  (* This will affect all of the virtio devices (if any). *)

+  let virtio_transitional =

+    guestcaps.gcaps_machine = Q35 && not guestcaps.gcaps_virtio_1_0 in

+  let virtio_model =

+    if virtio_transitional then "virtio-transitional" else "virtio" in

+

   (* Fixed and removable disks. *)

   let () =

-    let make_disk bus_name drive_prefix i = function

+    let make_disk bus_name ?(viotrans = false) drive_prefix i = function

     | BusSlotEmpty -> Comment (sprintf "%s slot %d is empty" bus_name i)

     | BusSlotDisk d ->

        let outdisk = outdisk_name d.s_disk_id in

-        e "disk" [

-          "type", if pool = None then "file" else "volume";

-          "device", "disk"

-        ] [

+        e "disk" (

+          [

+            "type", if pool = None then "file" else "volume";

+            "device", "disk"

+          ] @ if (viotrans) then [ "model", "virtio-transitional" ] else []

+        ) [

           e "driver" [

             "name", "qemu";

             "type", output_format;

@@ -364,7 +372,7 @@ let create_libvirt_xml ?pool source inspect

     in

     List.push_back_list devices

-      (List.mapi (make_disk "virtio" "vd")

+      (List.mapi (make_disk "virtio" ~viotrans:virtio_transitional "vd")

                  (Array.to_list target_buses.target_virtio_blk_bus));

     let ide_disks =

       match guestcaps.gcaps_machine with

@@ -392,7 +400,7 @@ let create_libvirt_xml ?pool source inspect

   let nics =

     let net_model =

       match guestcaps.gcaps_net_bus with

-      | Virtio_net -> "virtio" | E1000 -> "e1000" | RTL8139 -> "rtl8139" in

+      | Virtio_net -> virtio_model | E1000 -> "e1000" | RTL8139 -> "rtl8139" in

     List.map (

       fun { s_mac = mac; s_vnet_type = vnet_type; s_vnet = vnet } ->

         let vnet_type_str =

@@ -483,7 +491,7 @@ let create_libvirt_xml ?pool source inspect

   (* Miscellaneous KVM devices. *)

   if guestcaps.gcaps_virtio_rng then

     List.push_back devices (

-      e "rng" ["model", "virtio"] [

+      e "rng" ["model", virtio_model] [

         (* XXX Using /dev/urandom requires libvirt >= 1.3.4.  Libvirt

          * was broken before that.

          *)

@@ -496,7 +504,7 @@ let create_libvirt_xml ?pool source inspect

   List.push_back devices (

     e "memballoon"

       ["model",

-       if guestcaps.gcaps_virtio_balloon then "virtio" else "none"]

+       if guestcaps.gcaps_virtio_balloon then virtio_model else "none"]

       []

   );

   if guestcaps.gcaps_isa_pvpanic then

@@ -508,7 +516,7 @@ let create_libvirt_xml ?pool source inspect

   List.push_back devices (

     e "viosock"

       ["model",

-        if guestcaps.gcaps_virtio_socket then "virtio" else "none"]

+        if guestcaps.gcaps_virtio_socket then virtio_model else "none"]

        []

   );

-- 

2.31.1