Re: [Qemu-devel] [PATCH V13 3/4] pc: add a Virtual Machine Generation ID device

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Mar 03, 2015 at 12:03:26PM +1100, David Gibson wrote:
> On Mon, 2 Mar 2015 22:06:22 +0100
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Mon, Mar 02, 2015 at 06:05:43PM +0100, Igor Mammedov wrote:
> > > On Sun, 1 Mar 2015 16:09:33 +0100
> > > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > > 
> > > > On Wed, Feb 25, 2015 at 05:08:52PM +0000, Igor Mammedov wrote:
> > > > > Based on Microsoft's sepecifications (paper can be dowloaded from
> > > > > http://go.microsoft.com/fwlink/?LinkId=260709), add a device
> > > > > description to the SSDT ACPI table and its implementation.
> > > > > 
> > > > > The GUID is set using "vmgenid.uuid" property.
> > > > > 
> > > > > Example of using vmgenid device:
> > > > >  -device vmgenid,id=FOO,uuid="324e6eaf-d1d1-4bf6-bf41-b9bb6c91fb87"
> > > > 
> > > > If you do this, doesn't windows then prompt for a driver?
> > > it doesn't since PCI_CLASS_MEMORY_RAM is displayed as driver less 
> > > "PCI standard RAM Controller" binding in device manager.
> > > 
> > > There was an issue with
> > >  virtio balloon device + pseries firmware + kernel bug
> > >  http://lists.gnu.org/archive/html/qemu-devel/2012-03/msg04704.html
> > > but it shouldn't be an issue for x86 targets with which device is
> > > supposed to be used.
> > > CCing David and Laszlo in case UEFI might do some crazy stuff like
> > > pseries firmware.
> > 
> > I have to say, if it's not RAM, using PCI_CLASS_MEMORY_RAM seems
> > wrong. Can't we tag it in ACPI in some way?
> 
> I agree.  PCI_CLASS_MEMORY_RAM means something quite specific, and this
> device isn't it.  AFAICT, this would break pseries guests exactly like
> the balloon device did before we removed the bogus class code.
> 
> I'm lacking context to see what the purpose of this device is, and
> whether we could ever want something similar on ppc64.
> 
> > I guess I can somewhat buy 0580 "other memory controller".
> > 
> > I think we also want some space for future expansion
> > in this device.
> > How about we reserve first 4K, and set bit 0 to mean
> > "has uuid"?
> > 
> > -- 
> > MST
> 
> 
> -- 
> David Gibson <dgibson@redhat.com>
> Senior Software Engineer, Virtualization, Red Hat


it just exposes a unique id as part of its BAR.