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[Xen-users] FW: AMD-Vi/Intel VT-d: Passthrough or virtualization?

Forgot to send this to the Xen Mailing List two days ago. Was wondering why it didn't got posted...

> I apologize that I don't have links for you, but VT-d and the K-series
> chips was brought up specifically in a Reddit AMA with an Intel
> architect a few months ago. He wrote something along the lines of:
> >VT-d was planned for support in the K-series chips, but late testing of the features on >the pre-production runs showed that they were failing Intel's feature tests, and VT-d >support was disabled on them as an unfortunate last-minute move.
> I got a little less upset about not being able to buy a 2600K, and
> decided to skip the generation of chips altogether. But reading that
> VT-d support will disappear entirely is hopefully too disappointing to
> be true.... :(
> Regards,
> Andrew Bobulsky

This Thread?

I had to click tons of times to load the 2xxx comments to be able to search the full Thread. The only time he replied to a VT-d comment was there. The question was:

2) why do the K edition chips not support VT-d, all off the non K chips support it, but the K do not? as some one who likes to overclock and test server OS builds this seams like it may be a problem eventually.

The response was:

2) I had not noticed this. I don't work on the SKUing, but I agree with your reasoning. I'll make a case for it thanks for bringing it to my attention.

So if it was THAT Thread, you understanded something totally different to what he said. Where Intel did disabled VT-d support due to a bug was LGA 2011 Sandy Bridge-E Processors. The C1 Stepping didn't had VT-d, but it was enabled after it got fixed on the C2 Stepping. And it didn't affected LGA 1155 Processors.

For as long as I can remember, Intel likes to play enabling/disabling features on certain models just to sell them for more profit on more expensive lines. Do you want ECC Memory support on a Uniprocessor computer? Then you need pretty much a Xeon E3, that while physically is the same die that some of the Desktop counterparts, they don't disable on purpose that feature on them. With VT-d is the same. And most non-K Haswell models launched a week or so ago do claim VT-d support. So your info seems to be totally wrong.

Also, I did a follow up question to the ASUS guy regarding VT-d support on their Motherboards, here:

His response in the next Post was this:
Contact your local support rep and see what they say. The info I gave you pertains to how it has been from HQ when I have asked for the past two gens. All 50 tests of vt-D would only work on Q series boards and not Z series.

Basically, he says that ASUS throwed a 50 test battery for VT-d on non-Q series Chipsets for Sandy Bridge and Ivy Bridge, and they don't pass some of these test. Without hard data of what test fails and what specific feature they use, I can't come up with a conclusion, as on Motherboards from other manufacturers things seems to work fine. I suppose a Xen developer would want to have a word with ASUS to get hard data about this issue.
However, I could believe that it can be an excuse just because the ASUS BIOS developers are extremely lazy to make things work as they should, as ASUS got an extremely bad reputation when it comes to comply with standards. An example here:

So not only their track record on VT-d support is lame compared to other manufacturers, on other features that the BIOS should announce, they suck too.

I would want to lobby to get a few hands working on a tool like the one I said here:

Even with my null Linux and Xen experience, I would still say that I would value a tool that says you what work and what doesn't, before you try it on the real thing.
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