With qemu4 an incompatible change was added to pc_piix, which makes it
practical impossible to migrate domUs started with qemu2 or qemu3 to
newer qemu versions. Commit 7fccf2a06890e3bc3b30e29827ad3fb93fe88fea
added and enabled a new member "smbus_no_migration_support". In commit
4ab2f2a8aabfea95cc53c64e13b3f67960b27fdf the vmstate_acpi got new
elements, which are conditionally filled. As a result, an incoming
migration expected smbus related data unless smbus migration was
disabled for a given MachineClass. Since first commit forgot to handle
'xenfv', domUs started with qemu4 are incompatible with their qemu3
siblings.
Using other existing machine types, such as 'pc-i440fx-3.1', is not
possible because 'xenfv' creates the 'xen-platform' PCI device at
00:02.0, while all other variants to run a domU would create it at
00:04.0.
To cover both the existing and the broken case of 'xenfv' in a single
qemu binary, a new compatibility variant of 'xenfv-qemu4' must be added
which targets domUs started with qemu-4.0, qemu-4.1 and qemu-4.2. The
existing 'xenfv' restores compatibility of qemu5+ with qemu2/3.
Host admins who started domUs with qemu-4.x have to use a wrapper script
which appends '-machine xenfv-qemu4' to the device-model command line.
This is only required if there is no maintenance window which allows to
temporary shutdown the domU and restart it with a fixed device-model.
The wrapper script is as simple as this:
#!/bin/sh
exec /usr/bin/qemu-system-i386 "$@" -machine xenfv-qemu4
With xl this script will be enabled with device_model_override=, see
xl.cfg(5). To live migrate a domU, adjust the existing domU.cfg and pass
it to xl migrate or xl save/restore:
xl migrate -C new-domU.cfg domU remote-host
xl save domU CheckpointFile new-domU.cfg
xl restore new-domU.cfg CheckpointFile
With libvirt this script will be enabled with the <emulator> element in
domU.xml. Use 'virsh edit' prior 'virsh migrate' to replace the existing
<emulator> element to point it to the wrapper script.
Signed-off-by: Olaf Hering <o...@aepfle.de>
---
hw/i386/pc_piix.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index e6756216f9..ef23da88d9 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -948,11 +948,26 @@ DEFINE_PC_MACHINE(isapc, "isapc", pc_init_isa,
#ifdef CONFIG_XEN
+static void xenfv_qemu_4_x_machine_options(MachineClass *m)
+{
+ m->desc = "Xen Fully-virtualized PC (qemu 4.x compat)";
+ m->max_cpus = HVM_MAX_VCPUS;
+ m->default_machine_opts = "accel=xen";
+ m->smbus_no_migration_support = false;
+}
+
+DEFINE_PC_MACHINE(xenfv_qemu4, "xenfv-qemu4", pc_xen_hvm_init,
+ xenfv_qemu_4_x_machine_options);
+
static void xenfv_machine_options(MachineClass *m)
{
+ PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
+
m->desc = "Xen Fully-virtualized PC";
m->max_cpus = HVM_MAX_VCPUS;
m->default_machine_opts = "accel=xen";
+ m->smbus_no_migration_support = true;
+ pcmc->pvh_enabled = false;
}
DEFINE_PC_MACHINE(xenfv, "xenfv", pc_xen_hvm_init,
