Re: [Qemu-devel] [PATCH v8 4/8] ACPI: Add Virtual Machine Generation ID support

[Dr. David Alan Gilbert]

* Laszlo Ersek (address@hidden) wrote:
> CC Dave

This isn't an area I really understand; but if I'm
reading this right then 
   vmgenid is stored in fw_cfg?
   fw_cfg isn't migrated

So why should any changes to it get migrated, except if it's already
been read by the guest (and if the guest reads it again aftwards what's
it expected to read?)

Dave

> On 02/17/17 11:43, Igor Mammedov wrote:
> > On Thu, 16 Feb 2017 15:15:36 -0800
> > address@hidden wrote:
> > 
> >> From: Ben Warren <address@hidden>
> >>
> >> This implements the VM Generation ID feature by passing a 128-bit
> >> GUID to the guest via a fw_cfg blob.
> >> Any time the GUID changes, an ACPI notify event is sent to the guest
> >>
> >> The user interface is a simple device with one parameter:
> >>  - guid (string, must be "auto" or in UUID format
> >>    xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)
> > I've given it some testing with WS2012R2 and v4 patches for Seabios,
> > 
> > Windows is able to read initial GUID allocation and writeback
> > seems to work somehow:
> > 
> > (qemu) info vm-generation-id 
> > c109c09b-0e8b-42d5-9b33-8409c9dcd16c
> > 
> > vmgenid client in Windows reads it as 2 following 64bit integers:
> > 42d50e8bc109c09b:6cd1dcc90984339b
> > 
> > However update path/restore from snapshot doesn't
> > here is as I've tested it:
> > 
> > qemu-system-x86_64 -device vmgenid,id=testvgid,guid=auto -monitor stdio
> > (qemu) info vm-generation-id 
> > c109c09b-0e8b-42d5-9b33-8409c9dcd16c
> > (qemu) stop
> > (qemu) migrate "exec:gzip -c > STATEFILE.gz" 
> > (qemu) quit
> > 
> > qemu-system-x86_64 -device vmgenid,id=testvgid,guid=auto -monitor stdio
> > -incoming "exec: gzip -c -d STATEFILE.gz"
> > (qemu) info vm-generation-id 
> > 28b587fa-991b-4267-80d7-9cf28b746fe9
> > 
> > guest
> >  1. doesn't get GPE notification that it must receive
> >  2. vmgenid client in Windows reads the same value
> >       42d50e8bc109c09b:6cd1dcc90984339b
> 
> Hmmm, I wonder if we need something like this, in vmgenid_post_load():
> 
> commit 90c647db8d59e47c9000affc0d81754eb346e939
> Author: Dr. David Alan Gilbert <address@hidden>
> Date:   Fri Apr 15 12:41:30 2016 +0100
> 
>     Fix pflash migration
> 
> with the idea being that in a single device's post_load callback, we
> shouldn't perform machine-wide actions (post_load is likely for fixing
> up the device itself). If machine-wide actions are necessary, we should
> temporarily register a "vm change state handler", and do the thing once
> that handler is called (when the machine has been loaded fully and is
> about to continue execution).
> 
> Can you please try the attached patch on top? (Build tested only.)
> 
> Thanks!
> Laszlo

> diff --git a/include/hw/acpi/vmgenid.h b/include/hw/acpi/vmgenid.h
> index db7fa0e63303..a2ae450b1f56 100644
> --- a/include/hw/acpi/vmgenid.h
> +++ b/include/hw/acpi/vmgenid.h
> @@ -4,6 +4,7 @@
>  #include "hw/acpi/bios-linker-loader.h"
>  #include "hw/qdev.h"
>  #include "qemu/uuid.h"
> +#include "sysemu/sysemu.h"
>  
>  #define VMGENID_DEVICE           "vmgenid"
>  #define VMGENID_GUID             "guid"
> @@ -21,6 +22,7 @@ typedef struct VmGenIdState {
>      DeviceClass parent_obj;
>      QemuUUID guid;                /* The 128-bit GUID seen by the guest */
>      uint8_t vmgenid_addr_le[8];   /* Address of the GUID (little-endian) */
> +    VMChangeStateEntry *vmstate;
>  } VmGenIdState;
>  
>  static inline Object *find_vmgenid_dev(void)
> diff --git a/hw/acpi/vmgenid.c b/hw/acpi/vmgenid.c
> index 9f97b722761b..0ae1d56ff297 100644
> --- a/hw/acpi/vmgenid.c
> +++ b/hw/acpi/vmgenid.c
> @@ -177,10 +177,20 @@ static void vmgenid_set_guid(Object *obj, const char 
> *value, Error **errp)
>  /* After restoring an image, we need to update the guest memory and notify
>   * it of a potential change to VM Generation ID
>   */
> +static void postload_update_guest_cb(void *opaque, int running, RunState 
> state)
> +{
> +    VmGenIdState *vms = opaque;
> +
> +    qemu_del_vm_change_state_handler(vms->vmstate);
> +    vms->vmstate = NULL;
> +    vmgenid_update_guest(vms);
> +}
> +
>  static int vmgenid_post_load(void *opaque, int version_id)
>  {
>      VmGenIdState *vms = opaque;
> -    vmgenid_update_guest(vms);
> +    vms->vmstate = qemu_add_vm_change_state_handler(postload_update_guest_cb,
> +                                                    vms);
>      return 0;
>  }
>  

--
Dr. David Alan Gilbert / address@hidden / Manchester, UK