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Date: Thu, 9 Apr 2015 11:21:28 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Gustau P??rez <gperez@entel.upc.edu>
Subject: Re: No IOMMU/DMAR with DELL 3020
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On Thu, Apr 09, 2015 at 10:17:41AM +0200, Gustau P??rez wrote:
> 
>    Hi,
> 
>    I'm trying xen dom0 on a DELL optiplex 3020 machine. The machine runs:
> 
>          root@xen_test:~ # uname -arn
>          FreeBSD xen_test 11.0-CURRENT FreeBSD 11.0-CURRENT #0 r281184:
> 
>    The box has a core i5-4590 equipped with VT-d:
> 
>          root@xen_test:~ # dmesg|grep EPT
>          VT-x: PAT,HLT,MTF,PAUSE,EPT,UG,VPID
>          Secondary Processor
> Controls=0x7cff<APIC,EPT,DT,RDTSCP,x2APIC,VPID,WBINVD,UG,PAUSE-loop,RDRAND,INVPCID,VMFUNC,VMCS>
>          EPT Features=0x6334141<XO,PW4,UC,WB,2M,1G,INVEPT,AD,single,all>
> 
This is VT-x, not VT-d.

>    Also the box has the last BIOS firmware from its vendor (DELL).
> 
>    However, even if VT-d is there, iommu is not enabled. Booting in
> verbose mode shows me this:
> 
>           root@xen_test:~ # dmesg|grep DMAR
>           ACPI: No DMAR table found
> 
>    which is the reason iommu support isn't enabled.
This means that VT-d is 'not there'.

> 
>    Shouldn't be DMAR be detected if VT-d is there? Any info I can
> provide, let me know.

Check BIOS settings, there could be a knob which enables VT-d.
If there is no knob, you are out of lack.  OS or Xen requires DMAR
table filled by BIOS to detect and use VT-d hardware.