Re: [Qemu-devel] [PATCH V14 0/3] Virtual Machine Generation ID

[Yan Vugenfirer <yvugenfi@redhat.com>]

----- Original Message -----
> From: "Michael S. Tsirkin" <mst@redhat.com>
> To: "Igor Mammedov" <imammedo@redhat.com>
> Cc: ghammer@redhat.com, "Yan Vugenfirer" <yvugenfi@redhat.com>, qemu-devel@nongnu.org
> Sent: Sunday, April 19, 2015 10:52:37 AM
> Subject: Re: [Qemu-devel] [PATCH V14 0/3] Virtual Machine Generation ID
> 
> On Wed, Apr 15, 2015 at 03:59:09PM +0200, Igor Mammedov wrote:
> > On Wed, 15 Apr 2015 12:38:57 +0200
> > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > 
> > > On Tue, Mar 03, 2015 at 05:18:12PM +0100, Igor Mammedov wrote:
> > > > Changes since v13:
> > > >  * fix comment style to /*... */ in testcase
> > > >  * make BAR TARGET_PAGE_SIZE as required by spec
> > > >  * make BAR prefetchable, spec also says that it shouldn't be
> > > >    marked as non cached
> > > >  * ACPI part
> > > >     * merge separate VGID device with PCI device description
> > > >     * mark device as not shown in UI,
> > > >       it hides "VM Generation ID" device from device manager
> > > >       and leaves only "PCI Standard RAM Controller" device there
> > > 
> > > In an offline chat, Yan (Cc) mentioned that with windows guests,
> > > PCI rebalancing can move BAR values around.
> > > Yan, could you comment on-list please?
> > > Is there a way to force this, for testing?
> > > 

Yes. It is part of HCK test kit:
https://msdn.microsoft.com/en-us/library/windows/hardware/jj673015(v=vs.85).aspx#About_rebalance_tests


> > > ACPI spec mentions this:
> > > If a platform uses a PCI BAR Target operation region, an ACPI OS will
> > > not load a native device driver for the associated PCI function. For
> > > example, if any of the BARs in a PCI function are associated with a PCI
> > > BAR Target operation region, then the OS will assume that the PCI
> > > function is to be entirely under the control of the ACPI BIOS. No driver
> > > will be loaded. Thus, a PCI function can be used as a platform
> > > controller for some task (hot-plug PCI, and so on) that the ACPI BIOS
> > > performs.
> > It seems that WS2012R2 doesn't honor this part of spec,
> > it still tries to find matching driver and load it.
> 
> Interesting. Looking at msdn:
> https://msdn.microsoft.com/en-us/library/windows/hardware/ff563877(v=vs.85).aspx
> Looks like what windows does to rebalance is query device for
> rebalancing support, stop driver, rebalance, and restart driver.
> 
> If device has no driver, it seems likely windows will assume
> it's safe to rebalance the resources.
> 
> There's also a very old document:
> http://www.microsoft.com/whdc/connect/pci/PCI-rsc.mspx
> which says it's possible to implement _DSM method to deny rebalance
> requests.
> Alternatively, we could put this device behind a pci extender, e.g. as
> implemented by Marcel. The resources would then be limited by the _CRS
> or the root.
> 
> > > 
> > > This might also avoid driver prompt from windows?
> > it isn't.
> 
>