[Qemu-devel] [PATCH] Add machine type pc-1.0-qemu-kvm for live migrate compatibility with qemu-kvm

[Alex Bligh]

Add a machine type pc-1.0-qemu-kvm for live migrate compatibility
with qemu-kvm version 1.0.

This patch adds inbound migrate capability from qemu-kvm version
1.0. The main ideas are those set out in Cole Robinson's patch here:
http://pkgs.fedoraproject.org/cgit/qemu.git/tree/0001-Fix-migration-from-qemu-kvm.patch?h=f20
however, rather than patching statically (and breaking inbound
migration on existing machine types), I have added a new machine
type (pc-1.0-qemu-kvm) without affecting any other machine types.
The existing pc-1.0 machine type is renamed to pc-1.0-qemu-git,
with pc-1.0 becoming an alias for one or another, as selected
by a configure option (defaulting to pc-1.0-qemu-git, IE no
change).

Two aproaches are taken:

* In hw/timer/i8254_common.c, the VMSTATE_UINT32_TEST macro
 is used to test the version for the irq_disable flags,
 allowing version 3 or more, or version 2 for an inbound
 migrate from qemu-kvm (only).

* In hw/acpi/piix4.c, qemu-kvm incorrectly uses version 2 for
 a version 3 structure, causing acpi_load_old to be used.
 acpi_load_old detects this situation based on the machine type
 and restarts the attempt to load the vmstate using a
 customised VMStateDescription. The above cleaner approach is
 unavailable here.

I developed this on qemu 2.0 but have forward ported it (trivially)
to master. My testing has been on a VM live-migrated-to-file from
Ubuntu Precise qemu-kvm 1.0.

I have given this a moderate degree of testing but it could do
with more.

Note that certain hardware devices (including QXL) will not
migrate properly due to a fundamental difference in their internal
state between versions.

Also note that (as expected) migration from qemu-2.x to qemu-1.0
will not work, even if the machine types are the same.

Changes from v4

* Revert to using a machine type, but do not add alias machine types,
  configure options, or (potentially) change the meaning of
  pc-1.0 - leave this for distributions to ponder

* Add compat_props for qemu-kvm-migration to the PIIX4_PM driver
  and the i8259 pit-common driver.

Signed-off-by: Alex Bligh <address@hidden>
---
 hw/acpi/piix4.c                   |   26 +++++++++++++++++++++++---
 hw/i386/pc_piix.c                 |   27 +++++++++++++++++++++++++++
 hw/timer/i8254_common.c           |   18 +++++++++++++++++-
 include/hw/i386/pc.h              |    8 ++++++++
 include/hw/timer/i8254_internal.h |    1 +
 5 files changed, 76 insertions(+), 4 deletions(-)

diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
index b72b34e..5c68d69 100644
--- a/hw/acpi/piix4.c
+++ b/hw/acpi/piix4.c
@@ -86,6 +86,8 @@ typedef struct PIIX4PMState {
     Notifier cpu_added_notifier;
 
     MemHotplugState acpi_memory_hotplug;
+
+    bool qemu_kvm_migration;
 } PIIX4PMState;
 
 #define TYPE_PIIX4_PM "PIIX4_PM"
@@ -200,12 +202,26 @@ static const VMStateDescription vmstate_pci_status = {
     }
 };
 
+static const VMStateDescription vmstate_acpi;
+
 static int acpi_load_old(QEMUFile *f, void *opaque, int version_id)
 {
     PIIX4PMState *s = opaque;
     int ret, i;
     uint16_t temp;
 
+    /* If we are expecting the inbound migration to come from
+     * qemu-kvm 1.0, it will have a version_id of 2 but really
+     * be version 3, so call back the original vmstate_load_state
+     * with a different more tolerant vmstate descriptor
+     */
+    if (version_id == 2 && s->qemu_kvm_migration) {
+        VMStateDescription vmstate_acpi_compat = vmstate_acpi;
+        vmstate_acpi_compat.minimum_version_id = 2;
+        return vmstate_load_state(f, &vmstate_acpi_compat,
+                                  opaque, version_id);
+    }
+
     ret = pci_device_load(PCI_DEVICE(s), f);
     if (ret < 0) {
         return ret;
@@ -267,9 +283,11 @@ static const VMStateDescription vmstate_memhp_state = {
 };
 
 /* qemu-kvm 1.2 uses version 3 but advertised as 2
- * To support incoming qemu-kvm 1.2 migration, change version_id
- * and minimum_version_id to 2 below (which breaks migration from
- * qemu 1.2).
+ * To support incoming qemu-kvm 1.2 migration, we support
+ * via a command line option a change to minimum_version_id
+ * of 2 in a _compat structure; we can't do this all the time
+ * as using a minimum_version_id of 2 (rather than 3) would
+ * break migration from qemu-git 1.2.
  *
  */
 static const VMStateDescription vmstate_acpi = {
@@ -589,6 +607,8 @@ static Property piix4_pm_properties[] = {
                      use_acpi_pci_hotplug, true),
     DEFINE_PROP_BOOL("memory-hotplug-support", PIIX4PMState,
                      acpi_memory_hotplug.is_enabled, true),
+    DEFINE_PROP_BOOL("qemu-kvm-migration", PIIX4PMState,
+                     qemu_kvm_migration, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 7081c08..56555c1 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -644,6 +644,32 @@ static QEMUMachine pc_machine_v1_0 = {
     .hw_version = "1.0",
 };
 
+#define PC_COMPAT_1_0_QEMU_KVM \
+        PC_COMPAT_1_0,\
+        {\
+            .driver   = "cirrus-vga",\
+            .property = "vgamem_mb",\
+            .value    = stringify(16),\
+        },{\
+            .driver   = "pit-common",\
+            .property = "qemu-kvm-migration",\
+            .value    = "on",\
+        },{\
+            .driver   = "PIIX4_PM",\
+            .property = "qemu-kvm-migration",\
+            .value    = "on",\
+        }
+
+static QEMUMachine pc_machine_v1_0_qemu_kvm = {
+    PC_I440FX_1_2_MACHINE_OPTIONS,
+    .name = "pc-1.0-qemu-kvm",
+    .compat_props = (GlobalProperty[]) {
+        PC_COMPAT_1_0_QEMU_KVM,
+        { /* end of list */ }
+    },
+    .hw_version = "1.0",
+};
+
 #define PC_COMPAT_0_15 \
         PC_COMPAT_1_0
 
@@ -886,6 +912,7 @@ static void pc_machine_init(void)
     qemu_register_pc_machine(&pc_machine_v1_2);
     qemu_register_pc_machine(&pc_machine_v1_1);
     qemu_register_pc_machine(&pc_machine_v1_0);
+    qemu_register_pc_machine(&pc_machine_v1_0_qemu_kvm);
     qemu_register_pc_machine(&pc_machine_v0_15);
     qemu_register_pc_machine(&pc_machine_v0_14);
     qemu_register_pc_machine(&pc_machine_v0_13);
diff --git a/hw/timer/i8254_common.c b/hw/timer/i8254_common.c
index 07345f6..7f3e4e3 100644
--- a/hw/timer/i8254_common.c
+++ b/hw/timer/i8254_common.c
@@ -257,6 +257,14 @@ static int pit_dispatch_post_load(void *opaque, int 
version_id)
     return 0;
 }
 
+static bool has_irq_disabled(void *opaque, int version_id)
+{
+    PITCommonState *s = opaque;
+    return (version_id >= 3) ||
+        (version_id == 2 &&
+         s->qemu_kvm_migration);
+}
+
 static const VMStateDescription vmstate_pit_common = {
     .name = "i8254",
     .version_id = 3,
@@ -266,7 +274,8 @@ static const VMStateDescription vmstate_pit_common = {
     .pre_save = pit_dispatch_pre_save,
     .post_load = pit_dispatch_post_load,
     .fields = (VMStateField[]) {
-        VMSTATE_UINT32_V(channels[0].irq_disabled, PITCommonState, 3),
+        VMSTATE_UINT32_TEST(channels[0].irq_disabled, PITCommonState,
+                            has_irq_disabled),
         VMSTATE_STRUCT_ARRAY(channels, PITCommonState, 3, 2,
                              vmstate_pit_channel, PITChannelState),
         VMSTATE_INT64(channels[0].next_transition_time,
@@ -275,6 +284,12 @@ static const VMStateDescription vmstate_pit_common = {
     }
 };
 
+static Property pit_common_properties[] = {
+    DEFINE_PROP_BOOL("qemu-kvm-migration", PITCommonState,
+                     qemu_kvm_migration, false),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
 static void pit_common_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
@@ -287,6 +302,7 @@ static void pit_common_class_init(ObjectClass *klass, void 
*data)
      * done by board code.
      */
     dc->cannot_instantiate_with_device_add_yet = true;
+    dc->props = pit_common_properties;
 }
 
 static const TypeInfo pit_common_type = {
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index 1c0c382..e420dbc 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -346,6 +346,14 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
             .driver   = "ioh3420",\
             .property = COMPAT_PROP_PCP,\
             .value    = "off",\
+        },{\
+            .driver   = "pit-common",\
+            .property = "qemu-kvm-migration",\
+            .value    = "off",\
+        },{\
+            .driver   = "PIIX4_PM",\
+            .property = "qemu-kvm-migration",\
+            .value    = "off",\
         }
 
 #define PC_COMPAT_1_7 \
diff --git a/include/hw/timer/i8254_internal.h 
b/include/hw/timer/i8254_internal.h
index 61a1bfb..5f7ee36 100644
--- a/include/hw/timer/i8254_internal.h
+++ b/include/hw/timer/i8254_internal.h
@@ -55,6 +55,7 @@ typedef struct PITCommonState {
     MemoryRegion ioports;
     uint32_t iobase;
     PITChannelState channels[3];
+    bool qemu_kvm_migration;
 } PITCommonState;
 
 #define TYPE_PIT_COMMON "pit-common"
-- 
1.7.9.5