Re: [PATCH v3 3/4] pc & q35: Add new object pc-memory-layout.

[Don Slutz <dslutz@verizon.com>]

On 04/21/14 08:27, Paolo Bonzini wrote:
> Il 24/03/2014 19:55, Don Slutz ha scritto:
>> This new object has the property max-ram-below-4g.
>>
>> If you add enough PCI devices then all mmio for them will not fit
>> below 4G which may not be the layout the user wanted. This allows
>> you to increase the below 4G address space that PCI devices can use
>> (aka decrease ram below 4G) and therefore in more cases not have any
>> mmio that is above 4G.
>>
>> For example adding "-global pc-memory-layout.max-ram-below-4g=2G" to
>> the command line will limit the amount of ram that is below 4G to
>> 2G.
>
> Does Xen's firmware allow 64-bit BARs?

Yes.  But not all supported devices do.

> I'm wondering why this is not a problem on KVM.
>

I suspect that it is.  It only shows up when you add a lot of
PCI devices either directly or via pci pass through.  Also it
is more Xen focused because the default ram below 4G is
much larger so that 32 bit only guests can have a lot of ram.

> Also, overloading -global like this isn't the best long term choice.  We should get custom -machine properties in 2.1, we should use them.
>

I may have missed this.  Is this

[PATCH V3 0/5] remove QEMUMachine indirection from MachineClass

Or some patch that is yet to be posted?

(I did add this to qemu_machine_opts and changed to the current
way to handle:

Subject: 	Re: [Qemu-devel] [PATCH 1/1] vl.c: Add pci_hole_min_size machine option.
Date: 	Wed, 5 Mar 2014 08:46:33 +0200
From: 	Michael S. Tsirkin <mst@redhat.com>
To: 	Don Slutz <dslutz@verizon.com>
CC: 	<xen-devel@lists.xensource.com>, <qemu-devel@nongnu.org>, Anthony Liguori <aliguori@amazon.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>



On Tue, Mar 04, 2014 at 06:51:11PM -0500, Don Slutz wrote:
> On 03/04/14 17:20, Michael S. Tsirkin wrote:
> >On Tue, Mar 04, 2014 at 02:18:49PM -0500, Don Slutz wrote:
> >>On 03/04/14 11:58, Michael S. Tsirkin wrote:
> >>>On Tue, Mar 04, 2014 at 11:36:44AM -0500, Don Slutz wrote:
> >>>>On 03/04/14 02:34, Michael S. Tsirkin wrote:
> >>>>>On Thu, Feb 27, 2014 at 05:32:23PM -0500, Don Slutz wrote:
> >>>>>>This allows growing the pci_hole to the size needed.

...

> Yes. Also, please find a way to only add it to
> machine types that support it, instead of ignoring it
> silently for those that don't.

)

> Paolo