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Date: Wed, 24 Jul 2013 12:08:09 +0200
From: Igor Mammedov <imammedo@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: "Michael S. Tsirkin" <mst@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>, Paolo Bonzini <pbonzini@redhat.com>, Laszlo Ersek <lersek@redhat.com>, Andreas =?ISO-8859-1?B?RuRyYmVy?= <afaerber@suse.de>, David Gibson <david@gibson.dropbear.id.au>

On Wed, 24 Jul 2013 12:51:16 +0300
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Wed, Jul 24, 2013 at 09:01:51AM +0200, Gerd Hoffmann wrote:
> > On 07/24/13 08:01, Michael S. Tsirkin wrote:
> > > It turns out that some 32 bit windows guests crash
> > > if 64 bit PCI hole size is >2G.
> > 
> > Ah, *that* is the reason for winxp crashing with a 64bit hole.
> > 
> > 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.
> 
> > > Limit it to 2G for piix and q35 by default,
> > > add properties to let management override the hole size.
> > > 
> > > Examples:
> > > -global i440FX-pcihost.pci_hole64_size=137438953472
> > 
> > Do we really want specify this in bytes?  Using megabytes or gigabytes
> > instead looks more sane to me.
> > 
> > cheers,
> >   Gerd
> 
> I think that arbitrarily saying size is in gigabytes is
> confusing to users (in particular because there's no
> documentation for properties except their type).
> I intend to send a patch to properties that allows writing
> "size=1G" instead.
for size property you could take patches:
 [PATCH 04/16] qapi: make visit_type_size fallback to type_int
 [PATCH 05/16] qdev: Add SIZE type to qdev properties
from [PATCH 00/16 RFC v6] ACPI memory hotplug