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Date: Wed, 24 Jul 2013 12:51:16 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20130724095116.GB26778@redhat.com>
References: <20130724060104.GA18072@redhat.com> <51EF7BDF.2070503@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: Gerd Hoffmann <kraxel@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>, Paolo Bonzini <pbonzini@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 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.
Will this address your comment?