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From: Don Slutz <dslutz@verizon.com>
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Date: Thu, 20 Nov 2014 11:48:25 -0500
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Subject: Re: [Qemu-devel] [BUGFIX][PATCH for 2.2 v3 1/1] -machine
 vmport=auto: Fix handling of VMWare ioport emulation for xen
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To: Paolo Bonzini <pbonzini@redhat.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, Michael Tokarev <mjt@tls.msk.ru>, qemu-devel@nongnu.org, Don Slutz <dslutz@verizon.com>, Anthony Liguori <aliguori@amazon.com>, Stefan Hajnoczi <stefanha@redhat.com>

On 11/20/14 06:00, Paolo Bonzini wrote:
>
> On 20/11/2014 11:00, Dr. David Alan Gilbert wrote:
>>>> I'm still not sure why the configuration should differ for "-M pc"
>>>> depending on whether xen is enabled.
>> I think this goes back to:
>>
>> commit 1611977c3d8fdbdac6090cbd1f5555cee4aed6d9
>> Author: Anthony PERARD <anthony.perard@citrix.com>
>> Date:   Tue May 3 17:06:54 2011 +0100
>>
>>      pc, Disable vmport initialisation with Xen.
>>      
>>      This is because there is not synchronisation of the vcpu register
>>      between Xen and QEMU, so vmport can't work properly.
>>      
>>      This patch introduces no_vmport parameter to pc_basic_device_init.
>>      
>>      Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
>>      Signed-off-by: Alexander Graf <agraf@suse.de>
> Yes, but Xen has since implemented vmport (commit 37f9e258).  It's fine
> to have a conservative default for "-M xenfv" and possibly "-M pc-2.1",
> but "-M pc" can require the latest hypervisor.

The QEMU part of xen using vmport was done.  The code in xen will not be 
part
of xen 4.5 (expected to be released next month), it is currently 
scheduled for 4.6
(some time next year) and is planning to use "vmport=on" when it is 
enabled in xen.

You are right that "-M pc" can require a newer (yet to exist) 
hypervisor, but I feel
it will cause less confusion and allow QEMU 2.2 to be used unchanged 
with older
xen versions; if the default is kept unchanged.

    -Don Slutz

> Paolo