From mboxrd@z Thu Jan  1 00:00:00 1970
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH v3 04/16] hypervisor part of add vmware_port
	to xl.cfg
Date: Mon, 08 Sep 2014 11:43:15 -0400
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To: Andrew Cooper <andrew.cooper3@citrix.com>, Jan Beulich <JBeulich@suse.com>, xen-devel@lists.xen.org, Don Slutz <dslutz@verizon.com>
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On 09/08/2014 11:32 AM, Andrew Cooper wrote:
> On 08/09/14 16:22, Jan Beulich wrote:
>>>>> On 08.09.14 at 17:01, <boris.ostrovsky@oracle.com> wrote:
>>> I wonder whether we should enable #GP intercepts only when we know that
>>> the guest is VMware-aware (which we do as far as I can tell since we
>>> have a config option).
>> I didn't look at the patches themselves yes, but I very much expected
>> this to now be the case considering discussion on the earlier version.
>> If it's not, I'm not even sure looking at the new version is going to be
>> of much use...
>>
>> Jan
>>
> I find it incredibly hard to believe that VMWare do unconditional #GP
> exits, and looking at the Intel manual, you do not actually need to
> intercept #GP faults.
>
> The "unconditional I/O exiting" control can be used to cherry-pick
> specific IO ports in combination with the IO port bitmap, ahead of the
> #GP fault due to a failure of IOPL.  I would expect AMD has a similar
> option.

Yes, it does. However, I believe #GP intercept has been added so that IO 
access can be made from guest's ring 3 as well, not to handle IO access 
in general.

Having said that, I don't remember seeing updates to IO permissions map 
in the patch.

-boris