Re: [Qemu-devel] [PATCH v5 5/5] nvdimm acpi: add _CRS

[Igor Mammedov]

On Mon, 7 Mar 2016 18:19:46 +0200
"Michael S. Tsirkin" <address@hidden> wrote:

> On Mon, Mar 07, 2016 at 05:17:19PM +0100, Igor Mammedov wrote:
> > > > So what would happen when PCI MMIO BAR would be mapped over above range,
> > > > since guest thinks it's free to use it as unused resource?    
> > > 
> > > IIRC, allocating MMIO BAR over RAM would make the MMIO invisible,
> > > irrespective of whether the RAM range is being used for anything.  
> > An then driver would start writing 'garbage' to RAM, resulting in
> > strange guest behavior and not work PCI device.  
> 
> Do you observe such behaviour?
> 
> > that's why reserving region is a good idea if it could be done.  
> 
> Which region? Reserve all of RAM in _CRS?
Ops, I'm wrong here since PCI0._CRS doesn't include RAM, it's
not needed to reserve region there.

> 
> > >   
> > > >     
> > > > >     
> > > > > > So we should either reserve range or punch a hole in PCI0._CRS.
> > > > > > Reserving ranges is simpler and that's what we've switched to
> > > > > > from manual hole punching, see PCI/CPU/Memory hotplug and other
> > > > > > motherboard resources.      
>