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

[David Gibson]

On Mon, 2 Mar 2015 22:06:22 +0100
"Michael S. Tsirkin" <address@hidden> 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" <address@hidden> 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 <address@hidden>
Senior Software Engineer, Virtualization, Red Hat

pgpI_Q9Wew7bG.pgp
Description: OpenPGP digital signature