Re: [Xen-devel] Intel Xeon E5620 CPU and VT-d (IOMMU) support?

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Jun 02, 2010 at 07:40:07PM +0300, Pasi Kärkkäinen wrote:
> Hello,
> 
> I'm planning to upgrade my testbox and I was checking for hardware options.
> Can someone verify if Intel Xeon E5620 CPU supports (or doesn't support) VT-d 
> IOMMU?
> 
> I'm asking because Intel website doesn't mention VT-d for E5620:
> http://ark.intel.com/Product.aspx?id=47925
> 
> .. but it does for some (older) CPUs (E5520):
> http://ark.intel.com/Product.aspx?id=40200
> 
> The chipset I'm planning to get (Intel 5520 Tylersburg) does have VT-d / 
> IOMMU support listed.

So one thing I didn't know was that you need equivalant number of DMAR
entries for the IO-APICs on your motherboard. If you have three IO-APICs (like, 
this
SuperMicro X8something), you need three DMAR entries - mine only has
one. Which means that VT-d is turned off (Xen and both Linux baremetal
do this) as it can't do its magic on the other IO-APICs to re-route the IRQs
to the guest. You can hack the code to re-enable it, but then you must
disable the x2APIC.


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