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Re: [Xen-devel] Xen 4.3 development update

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 

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?


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