Re: Xen 4.3 development update

[George Dunlap <george.dunlap@eu.citrix.com>]

On 07/05/13 23:23, James Harper wrote:
>>> A couple of questions:
>>>
>>> - Does Citrix XenServer Windows PV driver work with vanilla Xen 4.2.x? I
>> remember someone complaining on the list that it doesn't work.. (but I'm
>> not sure about that).
>>
>> I did a quick test of the XS 6.0.2 drivers on unstable and they didn't
>> work.  Didn't do any debugging, however.
>>
>>> - Does GPLPV do the lazy patching for WinXP on AMD?
>> I highly doubt it, but you'd have to ask James Harper.
>>
> GPLPV does do some TPR patching. You need to add the /PATCHTPR option to your boot.ini. It works for 2000 as well (and 2003 before MS stopped using TPR at all in sp2), if anyone cares :)
>
> For AMD, TPR access is changed to a LOCK MOVE CR8 instruction which enables setting of TPR without a VMEXIT. For Intel, TPR writes are only done if it would change the value of TPR, and reads are always done from a cached value. I guess this is what you mean by 'lazy'.
>
> I think xen itself does TPR optimisation for Intel these days so this may be unnecessary.
>
> It certainly makes a big difference for XP.

Well the context of this thread is a set of changes that makes the 
non-lazy TPR exits *much much* more expensive on AMD hardware.  The 
existence of a widely-available set of drivers as a work-round would be 
a pretty important factor in how we decide to proceed.

So if I just download your latest drivers and add /PATCHTPR on the 
boot.ini, the AMD TPR patching should work?

  -George