Re: [Qemu-devel] [PATCH v5 05/10] ACPI: Add Virtual Machine Generation ID support

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 6 Feb 2017 19:41:36 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Mon, Feb 06, 2017 at 09:29:30AM -0800, Ben Warren wrote:
> > 
> >     On Feb 6, 2017, at 8:15 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > 
> >     On Sun, Feb 05, 2017 at 01:12:00AM -0800, ben@skyportsystems.com wrote:
> > 
> >         From: Ben Warren <ben@skyportsystems.com>
> > 
> >         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)
> > 
> >         Signed-off-by: Ben Warren <ben@skyportsystems.com>
> > 
[...]

> > 
> > This variable name was suggested by Laszlo.  the ‘a’ in ‘vgia’ refers to
> > address, but I’ll add some comments.  
> 
> vmgenid_addr_le?
> 
> 
> >     How about we make it 8 byte so it's future proof?
> > 
> > I can do that, but a previous conversation we had made it clear that guests
> > would never allocate above 4GB so 64 bits wasn’t necessary.  
> 
> Right, it's just very painful to change once we make it 32 bit.
I'd keep it 32 bit since it's in variable in global AML context and our
table revision is 1, so per spec OSPM should handle it as 32 number.
Chances of guest survival on boot would depend on AML interpreter tolerance
to AML errors, which for windows usually is 0 and leads to non obvious BSOD.
If we leave DWORD, even XP will be able to boot fine and only report
unknown device.