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Date: Wed, 24 Jul 2013 16:14:11 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20130724131411.GB29428@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] pc: limit 64 bit hole to 2G by default
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, Eduardo Habkost <ehabkost@redhat.com>, qemu-devel@nongnu.org, Isaku Yamahata <yamahata@valinux.co.jp>, Alex Williamson <alex.williamson@redhat.com>, Gerd Hoffmann <kraxel@redhat.com>, Laszlo Ersek <lersek@redhat.com>, Andreas =?iso-8859-1?Q?F=E4rber?= <afaerber@suse.de>, David Gibson <david@gibson.dropbear.id.au>

On Wed, Jul 24, 2013 at 02:59:18PM +0200, Paolo Bonzini wrote:
> Il 24/07/2013 11:51, Michael S. Tsirkin ha scritto:
> > > Current seabios uses a slightly different approach: the 64bit hole is
> > > present only in case it is actually used to map bars there, and seabios
> > > tries to fit everything into the 32bit hole first.
> > 
> > Yes. But this doesn't work with device hotplug.
> 
> Are you preserving that behavior for older machine types?

Older machine types (1.5 and back) don't report PCI hole size to guests
so there's nothing to preserve.
This means there's not much I can do for pc-1.5: as before this
patch, hotplug of devices with large BARs won't work,
and some windows guests will crash if a device with a huge
BAR is added statically.

> (Also, what happens if you do -global i440FX-pcihost.pci_hole64_size=0?
>  Does that return a _CRS with only the 32-bit hole)?
> 
> Paolo

Yes.