live migrating hvm from 4.4 to 4.5 fails due to kvmvapic

live migrating hvm from 4.4 to 4.5 fails due to kvmvapic

[Olaf Hering]

Migrating a HVM guest from staging-4.4 to staging-4.5 fails:

# cat /var/log/xen/qemu-dm-fv-x64-sles12sp1-clean--incoming.log
char device redirected to /dev/pts/4 (label serial0)
xen_ram_alloc: do not alloc f800000 bytes of ram at 0 when runstate is INMIGRATE
xen_ram_alloc: do not alloc 800000 bytes of ram at f800000 when runstate is INMIGRATE
xen_ram_alloc: do not alloc 10000 bytes of ram at 10000000 when runstate is INMIGRATE
xen_ram_alloc: do not alloc 40000 bytes of ram at 10010000 when runstate is INMIGRATE
Unknown savevm section or instance 'kvm-tpr-opt' 0
qemu-system-i386: load of migration failed: Invalid argument


Initially I thought we broke our sles12 xen, but for some reason xen.git fails
in the very same way. In 4.4 kvmvapic gets enabled, it gets migrated in the
"kvm-tpr-opt" VMStateDescription. The 4.5 qemu does not know about it because
'kvmvapic' is not enabled. As a result the entire savevm stream is rejected.

One thing to fix it in staging-4.5 is to introduce a dummy device which
handles a section named "kvm-tpr-opt". I already have a hack which does
that, and the migration proceeds. I will propose a patch to deal with
this part of the bug.

Unfortunately later the VM appears to be alive, but nothing happens in
it. I assume it gets no further interrupts. Guess I need help with this
part of the bug.


domU.cfg looks like this:

name="x"
memory=256
serial="pty"
builder="hvm"
boot="cd"
disk=[
        'file:/disk0.raw,hda,w',
        'file:/some.iso,hdc:cdrom,r',
]
vif=[
        'bridge=br0'
]
keymap="de"
vfb = [
        'type=vnc,vncunused=1,keymap=de'
]
usb=1
usbdevice='tablet'


Olaf

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Re: live migrating hvm from 4.4 to 4.5 fails due to kvmvapic

[Olaf Hering]

On Thu, May 12, Olaf Hering wrote:

> One thing to fix it in staging-4.5 is to introduce a dummy device which
> handles a section named "kvm-tpr-opt". I already have a hack which does
> that, and the migration proceeds. I will propose a patch to deal with
> this part of the bug.

Something like shown below.

> Unfortunately later the VM appears to be alive, but nothing happens in
> it. I assume it gets no further interrupts. Guess I need help with this
> part of the bug.


Olaf

---
 hw/i386/Makefile.objs    |    1 
 hw/i386/xen44_kvmvapic.c |  147 +++++++++++++++++++++++++++++++++++++++++++++++
 xen-hvm.c                |    3 
 3 files changed, 151 insertions(+)

--- a/hw/i386/Makefile.objs
+++ b/hw/i386/Makefile.objs
@@ -5,6 +5,7 @@ obj-y += pc_sysfw.o
 obj-$(CONFIG_XEN) += ../xenpv/ xen/
 
 obj-y += kvmvapic.o
+obj-y += xen44_kvmvapic.o
 obj-y += acpi-build.o
 obj-y += bios-linker-loader.o
 hw/i386/acpi-build.o: hw/i386/acpi-build.c hw/i386/acpi-dsdt.hex \
--- /dev/null
+++ b/hw/i386/xen44_kvmvapic.c
@@ -0,0 +1,147 @@
+/*
+ * Copy of kvmvapic to allow migration from xen-4.4 qemu-xen with "kvm-tpr-opt"
+ *
+ * Copyright (C) 2007-2008 Qumranet Technologies
+ * Copyright (C) 2012      Jan Kiszka, Siemens AG
+ *
+ * This work is licensed under the terms of the GNU GPL version 2, or
+ * (at your option) any later version. See the COPYING file in the
+ * top-level directory.
+ */
+#include "sysemu/sysemu.h"
+#include "sysemu/cpus.h"
+#include "sysemu/kvm.h"
+#include "hw/i386/apic_internal.h"
+#include "hw/sysbus.h"
+#include "hw/xen/xen.h"
+
+typedef struct VAPICHandlers {
+    uint32_t set_tpr;
+    uint32_t set_tpr_eax;
+    uint32_t get_tpr[8];
+    uint32_t get_tpr_stack;
+} QEMU_PACKED VAPICHandlers;
+
+typedef struct GuestROMState {
+    char signature[8];
+    uint32_t vaddr;
+    uint32_t fixup_start;
+    uint32_t fixup_end;
+    uint32_t vapic_vaddr;
+    uint32_t vapic_size;
+    uint32_t vcpu_shift;
+    uint32_t real_tpr_addr;
+    VAPICHandlers up;
+    VAPICHandlers mp;
+} QEMU_PACKED GuestROMState;
+
+typedef struct VAPICROMState {
+    SysBusDevice busdev;
+    MemoryRegion io;
+    MemoryRegion rom;
+    uint32_t state;
+    uint32_t rom_state_paddr;
+    uint32_t rom_state_vaddr;
+    uint32_t vapic_paddr;
+    uint32_t real_tpr_addr;
+    GuestROMState rom_state;
+    size_t rom_size;
+    bool rom_mapped_writable;
+} VAPICROMState;
+
+#define TYPE_XEN_KVMVAPIC "xen_kvmvapic" /* copy of "kvmvapic" */
+
+static void xen44_vapic_realize(DeviceState *dev, Error **errp)
+{
+    fprintf(stderr, "%s(%u) dev %p\n", __func__, __LINE__, dev);
+}
+
+static int xen44_vapic_post_load(void *opaque, int version_id)
+{
+    if (xen_enabled()) {
+        int i;
+        fprintf(stderr, "%s(%u) %p 0x%x\n", __func__, __LINE__, opaque, version_id);
+        for (i = 12; i > 0; i--) {
+	    sleep(1);
+            fprintf(stderr, "%s(%u) sleep %d %ld\n", __func__, __LINE__, i, (long)getpid());
+	}
+    }
+    return 0;
+}
+
+static const VMStateDescription vmstate_handlers = {
+    .name = "kvmvapic-handlers",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .minimum_version_id_old = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(set_tpr, VAPICHandlers),
+        VMSTATE_UINT32(set_tpr_eax, VAPICHandlers),
+        VMSTATE_UINT32_ARRAY(get_tpr, VAPICHandlers, 8),
+        VMSTATE_UINT32(get_tpr_stack, VAPICHandlers),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static const VMStateDescription vmstate_guest_rom = {
+    .name = "kvmvapic-guest-rom",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .minimum_version_id_old = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_UNUSED(8),     /* signature */
+        VMSTATE_UINT32(vaddr, GuestROMState),
+        VMSTATE_UINT32(fixup_start, GuestROMState),
+        VMSTATE_UINT32(fixup_end, GuestROMState),
+        VMSTATE_UINT32(vapic_vaddr, GuestROMState),
+        VMSTATE_UINT32(vapic_size, GuestROMState),
+        VMSTATE_UINT32(vcpu_shift, GuestROMState),
+        VMSTATE_UINT32(real_tpr_addr, GuestROMState),
+        VMSTATE_STRUCT(up, GuestROMState, 0, vmstate_handlers, VAPICHandlers),
+        VMSTATE_STRUCT(mp, GuestROMState, 0, vmstate_handlers, VAPICHandlers),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static const VMStateDescription vmstate_xen44_vapic = {
+    .name = "kvm-tpr-opt",      /* compatible with qemu-kvm VAPIC */
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .minimum_version_id_old = 1,
+    .post_load = xen44_vapic_post_load,
+    .fields = (VMStateField[]) {
+        VMSTATE_STRUCT(rom_state, VAPICROMState, 0, vmstate_guest_rom,
+                       GuestROMState),
+        VMSTATE_UINT32(state, VAPICROMState),
+        VMSTATE_UINT32(real_tpr_addr, VAPICROMState),
+        VMSTATE_UINT32(rom_state_vaddr, VAPICROMState),
+        VMSTATE_UINT32(vapic_paddr, VAPICROMState),
+        VMSTATE_UINT32(rom_state_paddr, VAPICROMState),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static void xen44_vapic_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    fprintf(stderr, "%s(%u) klass %p data %p\n", __func__, __LINE__, klass, data);
+    dc->vmsd    = &vmstate_xen44_vapic;
+    dc->realize = xen44_vapic_realize;
+}
+
+static const TypeInfo xen44_vapic_type = {
+    .name          = TYPE_XEN_KVMVAPIC,
+    .parent        = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(VAPICROMState),
+    .class_init    = xen44_vapic_class_init,
+};
+
+static void xen44_vapic_register(void)
+{
+    fprintf(stderr, "%s(%u)\n", __func__, __LINE__);
+    type_register_static(&xen44_vapic_type);
+}
+
+type_init(xen44_vapic_register);
+
--- a/xen-hvm.c
+++ b/xen-hvm.c
@@ -15,6 +15,7 @@
 #include "hw/i386/apic-msidef.h"
 #include "hw/xen/xen_common.h"
 #include "hw/xen/xen_backend.h"
+#include "hw/sysbus.h"
 #include "qmp-commands.h"
 
 #include "sysemu/char.h"
@@ -161,6 +162,8 @@ static void xen_set_irq(void *opaque, in
 
 qemu_irq *xen_interrupt_controller_init(void)
 {
+    DeviceState *vapic = sysbus_create_simple("kvmvapic", -1, NULL);
+
     return qemu_allocate_irqs(xen_set_irq, NULL, 16);
 }
 

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Re: live migrating hvm from 4.4 to 4.5 fails due to kvmvapic

[Stefano Stabellini]

On Thu, 12 May 2016, Olaf Hering wrote:
> On Thu, May 12, Olaf Hering wrote:
> 
> > One thing to fix it in staging-4.5 is to introduce a dummy device which
> > handles a section named "kvm-tpr-opt". I already have a hack which does
> > that, and the migration proceeds. I will propose a patch to deal with
> > this part of the bug.
> 
> Something like shown below.

Thanks for looking into this. I don't think that adding a dummy device
in QEMU is acceptable. This kind of problems is usually solved with
versioning the PC machine in QEMU, see all the pc_machine_* in
hw/i386/pc_piix.c. One specific version of the machine is supposed to
remain identical over multiple QEMU releases. In this case xenfv (or the
pc machine you are using, if you are not using xenfv) has to be always
identical. That's why I think we need to add kvmapic back to it for
compatibility. I know it sucks. But we can choose a different PC machine
with accel=xen for new VMs. 


> > Unfortunately later the VM appears to be alive, but nothing happens in
> > it. I assume it gets no further interrupts. Guess I need help with this
> > part of the bug.
> 
> 
>
> 
> ---
>  hw/i386/Makefile.objs    |    1 
>  hw/i386/xen44_kvmvapic.c |  147 +++++++++++++++++++++++++++++++++++++++++++++++
>  xen-hvm.c                |    3 
>  3 files changed, 151 insertions(+)
> 
> --- a/hw/i386/Makefile.objs
> +++ b/hw/i386/Makefile.objs
> @@ -5,6 +5,7 @@ obj-y += pc_sysfw.o
>  obj-$(CONFIG_XEN) += ../xenpv/ xen/
>  
>  obj-y += kvmvapic.o
> +obj-y += xen44_kvmvapic.o
>  obj-y += acpi-build.o
>  obj-y += bios-linker-loader.o
>  hw/i386/acpi-build.o: hw/i386/acpi-build.c hw/i386/acpi-dsdt.hex \
> --- /dev/null
> +++ b/hw/i386/xen44_kvmvapic.c
> @@ -0,0 +1,147 @@
> +/*
> + * Copy of kvmvapic to allow migration from xen-4.4 qemu-xen with "kvm-tpr-opt"
> + *
> + * Copyright (C) 2007-2008 Qumranet Technologies
> + * Copyright (C) 2012      Jan Kiszka, Siemens AG
> + *
> + * This work is licensed under the terms of the GNU GPL version 2, or
> + * (at your option) any later version. See the COPYING file in the
> + * top-level directory.
> + */
> +#include "sysemu/sysemu.h"
> +#include "sysemu/cpus.h"
> +#include "sysemu/kvm.h"
> +#include "hw/i386/apic_internal.h"
> +#include "hw/sysbus.h"
> +#include "hw/xen/xen.h"
> +
> +typedef struct VAPICHandlers {
> +    uint32_t set_tpr;
> +    uint32_t set_tpr_eax;
> +    uint32_t get_tpr[8];
> +    uint32_t get_tpr_stack;
> +} QEMU_PACKED VAPICHandlers;
> +
> +typedef struct GuestROMState {
> +    char signature[8];
> +    uint32_t vaddr;
> +    uint32_t fixup_start;
> +    uint32_t fixup_end;
> +    uint32_t vapic_vaddr;
> +    uint32_t vapic_size;
> +    uint32_t vcpu_shift;
> +    uint32_t real_tpr_addr;
> +    VAPICHandlers up;
> +    VAPICHandlers mp;
> +} QEMU_PACKED GuestROMState;
> +
> +typedef struct VAPICROMState {
> +    SysBusDevice busdev;
> +    MemoryRegion io;
> +    MemoryRegion rom;
> +    uint32_t state;
> +    uint32_t rom_state_paddr;
> +    uint32_t rom_state_vaddr;
> +    uint32_t vapic_paddr;
> +    uint32_t real_tpr_addr;
> +    GuestROMState rom_state;
> +    size_t rom_size;
> +    bool rom_mapped_writable;
> +} VAPICROMState;
> +
> +#define TYPE_XEN_KVMVAPIC "xen_kvmvapic" /* copy of "kvmvapic" */
> +
> +static void xen44_vapic_realize(DeviceState *dev, Error **errp)
> +{
> +    fprintf(stderr, "%s(%u) dev %p\n", __func__, __LINE__, dev);
> +}
> +
> +static int xen44_vapic_post_load(void *opaque, int version_id)
> +{
> +    if (xen_enabled()) {
> +        int i;
> +        fprintf(stderr, "%s(%u) %p 0x%x\n", __func__, __LINE__, opaque, version_id);
> +        for (i = 12; i > 0; i--) {
> +	    sleep(1);
> +            fprintf(stderr, "%s(%u) sleep %d %ld\n", __func__, __LINE__, i, (long)getpid());
> +	}
> +    }
> +    return 0;
> +}
> +
> +static const VMStateDescription vmstate_handlers = {
> +    .name = "kvmvapic-handlers",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .minimum_version_id_old = 1,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_UINT32(set_tpr, VAPICHandlers),
> +        VMSTATE_UINT32(set_tpr_eax, VAPICHandlers),
> +        VMSTATE_UINT32_ARRAY(get_tpr, VAPICHandlers, 8),
> +        VMSTATE_UINT32(get_tpr_stack, VAPICHandlers),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
> +static const VMStateDescription vmstate_guest_rom = {
> +    .name = "kvmvapic-guest-rom",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .minimum_version_id_old = 1,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_UNUSED(8),     /* signature */
> +        VMSTATE_UINT32(vaddr, GuestROMState),
> +        VMSTATE_UINT32(fixup_start, GuestROMState),
> +        VMSTATE_UINT32(fixup_end, GuestROMState),
> +        VMSTATE_UINT32(vapic_vaddr, GuestROMState),
> +        VMSTATE_UINT32(vapic_size, GuestROMState),
> +        VMSTATE_UINT32(vcpu_shift, GuestROMState),
> +        VMSTATE_UINT32(real_tpr_addr, GuestROMState),
> +        VMSTATE_STRUCT(up, GuestROMState, 0, vmstate_handlers, VAPICHandlers),
> +        VMSTATE_STRUCT(mp, GuestROMState, 0, vmstate_handlers, VAPICHandlers),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
> +static const VMStateDescription vmstate_xen44_vapic = {
> +    .name = "kvm-tpr-opt",      /* compatible with qemu-kvm VAPIC */
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .minimum_version_id_old = 1,
> +    .post_load = xen44_vapic_post_load,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_STRUCT(rom_state, VAPICROMState, 0, vmstate_guest_rom,
> +                       GuestROMState),
> +        VMSTATE_UINT32(state, VAPICROMState),
> +        VMSTATE_UINT32(real_tpr_addr, VAPICROMState),
> +        VMSTATE_UINT32(rom_state_vaddr, VAPICROMState),
> +        VMSTATE_UINT32(vapic_paddr, VAPICROMState),
> +        VMSTATE_UINT32(rom_state_paddr, VAPICROMState),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
> +static void xen44_vapic_class_init(ObjectClass *klass, void *data)
> +{
> +    DeviceClass *dc = DEVICE_CLASS(klass);
> +
> +    fprintf(stderr, "%s(%u) klass %p data %p\n", __func__, __LINE__, klass, data);
> +    dc->vmsd    = &vmstate_xen44_vapic;
> +    dc->realize = xen44_vapic_realize;
> +}
> +
> +static const TypeInfo xen44_vapic_type = {
> +    .name          = TYPE_XEN_KVMVAPIC,
> +    .parent        = TYPE_SYS_BUS_DEVICE,
> +    .instance_size = sizeof(VAPICROMState),
> +    .class_init    = xen44_vapic_class_init,
> +};
> +
> +static void xen44_vapic_register(void)
> +{
> +    fprintf(stderr, "%s(%u)\n", __func__, __LINE__);
> +    type_register_static(&xen44_vapic_type);
> +}
> +
> +type_init(xen44_vapic_register);
> +
> --- a/xen-hvm.c
> +++ b/xen-hvm.c
> @@ -15,6 +15,7 @@
>  #include "hw/i386/apic-msidef.h"
>  #include "hw/xen/xen_common.h"
>  #include "hw/xen/xen_backend.h"
> +#include "hw/sysbus.h"
>  #include "qmp-commands.h"
>  
>  #include "sysemu/char.h"
> @@ -161,6 +162,8 @@ static void xen_set_irq(void *opaque, in
>  
>  qemu_irq *xen_interrupt_controller_init(void)
>  {
> +    DeviceState *vapic = sysbus_create_simple("kvmvapic", -1, NULL);
> +
>      return qemu_allocate_irqs(xen_set_irq, NULL, 16);
>  }
>  
> 

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Re: live migrating hvm from 4.4 to 4.5 fails due to kvmvapic

[Wei Liu]

On Thu, May 12, 2016 at 05:48:13PM +0200, Olaf Hering wrote:
> Migrating a HVM guest from staging-4.4 to staging-4.5 fails:
> 
> # cat /var/log/xen/qemu-dm-fv-x64-sles12sp1-clean--incoming.log
> char device redirected to /dev/pts/4 (label serial0)
> xen_ram_alloc: do not alloc f800000 bytes of ram at 0 when runstate is INMIGRATE
> xen_ram_alloc: do not alloc 800000 bytes of ram at f800000 when runstate is INMIGRATE
> xen_ram_alloc: do not alloc 10000 bytes of ram at 10000000 when runstate is INMIGRATE
> xen_ram_alloc: do not alloc 40000 bytes of ram at 10010000 when runstate is INMIGRATE
> Unknown savevm section or instance 'kvm-tpr-opt' 0
> qemu-system-i386: load of migration failed: Invalid argument
> 
> 
> Initially I thought we broke our sles12 xen, but for some reason xen.git fails
> in the very same way. In 4.4 kvmvapic gets enabled, it gets migrated in the
> "kvm-tpr-opt" VMStateDescription. The 4.5 qemu does not know about it because
> 'kvmvapic' is not enabled. As a result the entire savevm stream is rejected.
> 
> One thing to fix it in staging-4.5 is to introduce a dummy device which
> handles a section named "kvm-tpr-opt". I already have a hack which does
> that, and the migration proceeds. I will propose a patch to deal with
> this part of the bug.
> 
> Unfortunately later the VM appears to be alive, but nothing happens in
> it. I assume it gets no further interrupts. Guess I need help with this
> part of the bug.
> 
> 

My fear is that the VM might actually be poking at that device. That
explains why the migration is successful but the VM is not functioning.
I think the first thing would be to confirm whether the guest is
actually using that device.

For newly created guest on xen 4.4, you will need some rune in guest cfg
file to explicitly disable that device. There is device_model_args=
option for you to do that.

For guests that are already running, you can try to massage the guest
cfg before sending, post receiving but before creating, or hack libxl to
add that kvm device.

But all things said above are just workaround. Unfortunately I don't see
an easy way of solving this off the top of my head.

Wei.

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Re: live migrating hvm from 4.4 to 4.5 fails due to kvmvapic

[Olaf Hering]

[-- Attachment #1.1: Type: text/plain, Size: 1366 bytes --]

As a followup to the issue below, and the one which "just" popped in in
qemu-2.6+:

Why is the machine description for xen not fixed?

Shouldnt the be some sort of verification of old and new 'xenfv' when a
new qemu rc1 is done?
Is there a way to dump the machine description in text form?

Olaf

On Fri, May 13, Stefano Stabellini wrote:

> On Thu, 12 May 2016, Olaf Hering wrote:
> > On Thu, May 12, Olaf Hering wrote:
> > 
> > > One thing to fix it in staging-4.5 is to introduce a dummy device which
> > > handles a section named "kvm-tpr-opt". I already have a hack which does
> > > that, and the migration proceeds. I will propose a patch to deal with
> > > this part of the bug.
> > 
> > Something like shown below.
> 
> Thanks for looking into this. I don't think that adding a dummy device
> in QEMU is acceptable. This kind of problems is usually solved with
> versioning the PC machine in QEMU, see all the pc_machine_* in
> hw/i386/pc_piix.c. One specific version of the machine is supposed to
> remain identical over multiple QEMU releases. In this case xenfv (or the
> pc machine you are using, if you are not using xenfv) has to be always
> identical. That's why I think we need to add kvmapic back to it for
> compatibility. I know it sucks. But we can choose a different PC machine
> with accel=xen for new VMs. 



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[-- Attachment #2: Type: text/plain, Size: 127 bytes --]

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Re: live migrating hvm from 4.4 to 4.5 fails due to kvmvapic

[Stefano Stabellini]

On Tue, 2 Aug 2016, Olaf Hering wrote:
> As a followup to the issue below, and the one which "just" popped in in
> qemu-2.6+:
> 
> Why is the machine description for xen not fixed?

xenfv comes from a time when QEMU didn't have machine description
versioning. To have versioning, it is possible to use a regular PC
machine plus accel=xen. I tried to change the libxl default from xenfv
to a versioned pc machine with accel=xen a couple of years back, but
unfortunately it created ABI incompatibilities, see:

http://marc.info/?i=alpine.DEB.2.02.1406121512360.13771%40kaball.uk.xensource.com


> Shouldnt the be some sort of verification of old and new 'xenfv' when a
> new qemu rc1 is done?

It would be great to have


> Is there a way to dump the machine description in text form?

I don't know, but people at qemu-devel might.

 
> On Fri, May 13, Stefano Stabellini wrote:
> 
> > On Thu, 12 May 2016, Olaf Hering wrote:
> > > On Thu, May 12, Olaf Hering wrote:
> > > 
> > > > One thing to fix it in staging-4.5 is to introduce a dummy device which
> > > > handles a section named "kvm-tpr-opt". I already have a hack which does
> > > > that, and the migration proceeds. I will propose a patch to deal with
> > > > this part of the bug.
> > > 
> > > Something like shown below.
> > 
> > Thanks for looking into this. I don't think that adding a dummy device
> > in QEMU is acceptable. This kind of problems is usually solved with
> > versioning the PC machine in QEMU, see all the pc_machine_* in
> > hw/i386/pc_piix.c. One specific version of the machine is supposed to
> > remain identical over multiple QEMU releases. In this case xenfv (or the
> > pc machine you are using, if you are not using xenfv) has to be always
> > identical. That's why I think we need to add kvmapic back to it for
> > compatibility. I know it sucks. But we can choose a different PC machine
> > with accel=xen for new VMs. 

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