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Date: Mon, 7 Mar 2016 18:19:46 +0200
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Subject: Re: [Qemu-devel] [PATCH v5 5/5] nvdimm acpi: add _CRS
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To: Igor Mammedov <imammedo@redhat.com>
Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>, ehabkost@redhat.com, kvm@vger.kernel.org, gleb@kernel.org, mtosatti@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com, pbonzini@redhat.com, dan.j.williams@intel.com, rth@twiddle.net

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?

> > 
> > >   
> > > >   
> > > > > 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.