8 Replies Latest reply on Oct 29, 2012 4:13 PM by Beeckmans Olivier

    Complete VT-d support


      Hi all,


      I have recently bought a Intel Core I5-650 with Intel DQ57TM Board for my Homeserver.

      I will run this system as virtualisation host based on XEN.

      On the Intel-Homepage I saw that both components are VT-d capable and in the Board-Manual

      I could see that there is in option to enable or disable

      "Intel® Virtualization Technology for Directed I/O (VT-d)" in the bios.

      That was the reason a have bought it.


      On intel-Homepage on the VT-d explanation they say, that VT-d includeds

      "interrupt remapping / DMA passthrough" and so on.

      So I installed latest XEN 4.1.1 with latest DOM-0-Kernel and with

      scare I determined that "Interrupt-Remapping" is not supported.

      Here is my xm dmesg output:



      (XEN) Intel VT-d Snoop Control not enabled.
      (XEN) Intel VT-d Dom0 DMA Passthrough not enabled.
      (XEN) Intel VT-d Queued Invalidation not enabled.
      (XEN) Intel VT-d Interrupt Remapping not enabled.
      (XEN) I/O virtualisation enabled

      I can succesfully passthrough a device to guest but without interrupt-remapping and
      only with shared interrupt (XEN-DomU Config: pci_msitranslate=0).

      So I have searched a little bit around the web and have found that only
      intel core i7 and new sandy bridge CPU´s will
      completely support all VT-d features is that right?

      Here has someone made the same experience:
      I think Intel has to update there documentation for processors and boards.
      There is only one TAB with "VT-d Yes or No". So I thought ok the components will do it.
      There should be a extra tab with the sub-VT-d-Features.
      So I have spend a lot of money for nothing. I need interrupt-remapping.

      So before buy a  new system I will be SURE that ALL VT-d features will be supported.

      So what about this combination?

      Intel Core I5-2500T
      Intel DQ67SW Board

      Or what about this?
      Intel S1200BTS
      Intel E3-1220L

      For S1200BTS I found in the manuell bios settings to enable disable Interrupt Remapping and DMA Passthrough.
      But does the E31220L support this?

      Will this combination completely support all VT-d-
      relevant featurse (Interrupt Remapping....etc)???

        • 1. Re: Complete VT-d support

          In regards to your inquiries/comments, I have the following comments/suggestions:


          1. "...only intel core i7 and new sandy bridge CPU´s will completely support all VT-d features is that right?"
          I confirm that is not true.  It is important to look in the datasheet for the processor for the details regarding on which Intel® VT-d features are supported and which are not; here is the datasheet (see pages 36 and 37) for the 2nd Generation Intel® Core™ Processor Family Desktop and Intel® Pentium® Processor® Family Desktop, including the Intel(R) Core(TM) i7 Processor(s):




          Looking at datasheet of the Intel(R) Core(TM) i5 Processor i5-650, page 31 (click here), per se, on the other hand, it is stated "No support for interrupt remapping":


          2. "What about...[the Intel Core I5-2500T and Intel DQ67SW Board]"?
          I confirm the Intel(R) Desktop Board DQ67SW is among the boards that do support Intel VT with Directed I/O:




          The Intel(R) Desktop Board DQ57TM is listed there, too, and board-wise, I confirm the option for Interrupt Remapping to be either enabled or disabled is available as long as the processor does support Interrupt Remapping; see under "Security > Intel® VT for Directed I/O (VT-d)" (page 33) here:




          As for the datatsheet for the Intel(R) Core(TM) I5-2500T Processor, "Interrupt Remapping is supported"; see page 37 here:




          3. "What about...[the Intel(R) Xeon(TM) Processor E3-1220L]"?
          As for the datatsheet for this Intel(R) Xeon(TM) Processor, "Interrupt Remapping is supported"; see page 39 here:




          4. "Will this combination completely support all VT-d-relevant featurse (Interrupt Remapping....etc)???"
          I'd recommend referring to the datasheet of each processor to really confirm what is and what is not supported.


          As for the Intel(R) Server Board S1200BT, "Interrupt Remapping" is there, indeed, in the BIOS for it to be enabled or disabled:


          http://download.intel.com/support/motherboards/server/s1200bt/G13326-003_S1200BT_TPS_v1_0.pdf (page 74)

          • 2. Re: Complete VT-d support

            Thank you Salem_Intel!


            When I have a look into the datasheets it´s clear now.


            But I didn´t look so deep into the datasheets.

            I only saw VT-d supported. When I clicked on VT-d on homepage, I got the VT-d descripten.

            And there was written that "Interrupt-Remapping is a feature of VT-d".

            So it was clear to me that this CPU will do it.


            Maybe a documentation update on the homepage would be very fine for

            other consumers. Maybe a version number (Core I5-650 VT-d = 1.1 ; I5-2500T VT-d = 1.2) or

            something like that.


            But now it´s to late for me ;-).


            When I now look into the datasheets for the new core-i5-2500T and new Sandy-Bridge based XEONS (E3 - 1200 Series)

            there are also some VT-d features which are not supported. Just for interesting which CPU will support

            all features?


            I think I will run to:

            Server Board S1200BT or Supermicro X9-Series (X9SCA).


            Intel E3-1260L or Intel E3-1220L


            If I have understand you, the board just has to support VT-d.

            The subfeatures (Interrupt Remapping, DMA Passthrough....etc) are defined through the processor.

            Is that right? So I can take any Board for Xeon E3-1200 Series which has the Bios-Option to enable disable VT-d?

            Or has the board also hast to have an explicit option for interrupt remapping/etc. in bios like the S1200BT?

            • 3. Re: Complete VT-d support


              Thanks for the feedback!


              I confirm no current processor do provide support for all of the Intel(R) VT-d features:




              As for your last implied question, I confirm the chipset, the board, the BIOS and the processor must support Intel(R) VT-d.


              As for both, the Intel(R) Xeon(TM) Processor E3-1260L and Intel(R) Xeon(TM) Processor E3-1220L, "interrupt remapping is supported" (qtd. on page 39 of the datasheet).  Thus, indeed, "the subfeatures (Interrupt Remapping, DMA Passthrough....etc) are defined through the processor."  Whether or not you can enable/disable these in BIOS, that'd be something the BIOS will need to support.

              • 4. Re: Complete VT-d support

                What is the difference between VT-D and VT-X , ??

                • 5. Re: Complete VT-d support


                  Intel VT-x helps improve the fundamental flexibility and robustness of software-based virtualization solutions. It reduces VMM interventions by eliminating the need for the VMM to listen, trap and execute certain instructions on behalf of the guest Operating System (OS) as is required in software-only virtualization. It also provides hardware support for transferring platform control between the VMM and guest OSs, so when VMM intervention is required, handoffs are faster, more reliable and more secure.


                  As for Intel VT-d, this speeds data movement and eliminates much of the performance overhead by reducing the need for VMM involvement in managing I/O traffic. It accomplishes this by enabling the VMM to securely assign specific I/O devices to specific guest OSs. Each device is given a dedicated area in system memory that can be accessed only by the device and by its assigned guest OS.


                  Thus while the first deals with the processor support, the latter one does with the chipset support, in respect to the Intel(R) Virtualization Technology. You may want to refer to the following demo for more details:




                  Additionally, you could refer to the following document:




                  Hope that helps.

                  • 6. Re: Complete VT-d support

                    I was just courious , I am running a DX48BT2  with a Xeon   X-3380 , with Windows 7 Pro 64bit and the XP Mode works just fine . I just wanted to know what if any limitations do I have by have VT-x  insteed of  VTd ??

                    • 7. Re: Complete VT-d support

                      assuming you're using the "default solution" for XP Mode which is Windows (7) Virtual PC then its a non-issue as WVPC doesn't support VT-d


                      to slightly simply the abovestated excellent explanation;   VT-x affects the processor itself while VT-d affects the chipset/motherboard and onboard Intel peripheral components

                      • 8. Re: Complete VT-d support
                        Beeckmans Olivier

                        A few weeks ago, I bought an Intel motherboard S1200BTL and processor  E3-1230 V2. Because both support the PCI Passthrough to 100%.


                        Despite the fact that I'm using the latest BIOS with all the Vt-d option enabled, in Citrix XenServer 6.1 the PCi Passthrough is not 100% operational.


                        xe host-dmesg | grep VT-d


                        (XEN) Intel VT-d supported page sizes: 4kB.

                        (XEN) Intel VT-d Snoop Control enabled.

                        (XEN) Intel VT-d Dom0 DMA Passthrough not enabled.

                        (XEN) Intel VT-d Queued Invalidation enabled.

                        (XEN) Intel VT-d Interrupt Remapping enabled.

                        (XEN) Intel VT-d Shared EPT tables not enabled.


                        Therefore, I have a lot of difficulty with some PCIe cards.


                        I do not know how to fix this, My purchase was intended for passthrough and that don't run !


                        Thanks for your support


                        Olivier Beeckmans