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Re: [Xen-devel] [PATCH v3 04/16] hypervisor part of add vmware_port to xl.cfg

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@xxxxxxxxxx> 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...


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

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.


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