[PVE-User] IOMMU and AMD-Vi useful/recommended for Proxmox ?

[Iosif Peterfi]

On Thu, Aug 21, 2014 at 10:11 PM, <lst_hoe02 at kwsoft.de> wrote:

>
> Zitat von Iosif Peterfi <iosif.peterfi at gmail.com>:
>
>
>  On Thu, Aug 21, 2014 at 6:43 PM, <lst_hoe02 at kwsoft.de> wrote:
>>
>>
>>> Zitat von Gilberto Nunes <gilberto.nunes32 at gmail.com>:
>>>
>>>
>>>  http://en.wikipedia.org/wiki/X86_virtualization#I.2FO_MMU_
>>>
>>>> virtualization_.28AMD-Vi_and_VT-d.29
>>>>
>>>> 2014-08-21 13:06 GMT-03:00 <lst_hoe02 at kwsoft.de>:
>>>>
>>>>  Hello,
>>>>
>>>>>
>>>>> when inspecting the "dmesg" output on one of the PVE servers i got the
>>>>> follwoing:
>>>>>
>>>>> No AGP bridge found
>>>>> Node 0: aperture @ 0 size 32 MB
>>>>> Your BIOS doesn't leave a aperture memory hole
>>>>> Please enable the IOMMU option in the BIOS setup
>>>>> This costs you 64 MB of RAM
>>>>> Mapping aperture over 65536 KB of RAM @ 20000000
>>>>> PM: Registered nosave memory: 0000000020000000 - 0000000024000000
>>>>> AMD-Vi disabled by default: pass amd_iommu=on to enable
>>>>>
>>>>> My first action was to go to the BIOS (the machine is still test) and
>>>>> activated the IOMMU. The message stays the same. Next try was to set
>>>>> iommu=noaperture as boot parameter because it was suggested for machine
>>>>> having IOMMU but no AGP anymore. This lead to
>>>>>
>>>>> PCI-DMA: Using software bounce buffering for IO (SWIOTLB)
>>>>> Placing 64MB software IO TLB between ffff880020000000 -
>>>>> ffff880024000000
>>>>> software IO TLB at phys 0x20000000 - 0x24000000
>>>>>
>>>>> Which looks like the IOMMU emulated in software...
>>>>>
>>>>> This lead to the question what the real benefits of AMD-Vi / IOMMU are
>>>>> for
>>>>> Proxmox/KVM if they are disabled by default and can not be enabled
>>>>> straight
>>>>> forward as it looks like?
>>>>>
>>>>> The Board in question is a ASUS KCMA-D8, BIOS 3102 with two AMD Opteron
>>>>> 4226 CPUs.
>>>>>
>>>>>
>>>>>  Hm, yes. But this still lead to the question which boot parameter
>>> should
>>> be used if any:
>>>
>>> iommu=noaperture which looks like deaktivating GART IOMMU but also
>>> hardware IOMMU at all
>>> amd_iommu which should activate AMD-Vi which includes IOMMU
>>> no parameter which looks like using GART IOMMU but not AMD-Vi and only
>>> when IOMMU is enabled in BIOS
>>>
>>> or do i simply not need it at all if no passthrough of devices is
>>> required?
>>>
>>> me->confused
>>>
>>> Thanks
>>>
>>>
>>> Andreas
>>>
>>>
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>>> pve-user at pve.proxmox.com
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>>>
>>>
>>
>> Hello,
>>
>> From the original post I thought you were trying to activate AMD-Vi. What
>> are you trying to accomplish ?
>>
>> Regards,
>> Iosif
>>
>
> I try to find out if it is useful to activate the IOMMU and if yes, which
> kind of IOMMU and how. The default seams to use the GART (AGP?) based old
> style IOMMU. It would be interesting to hear if one could get a real
> benefit from using AMD-Vi instead which is the part which was invented for
> virtualization, no?
>
>
> Thanks
>
> Andreas
>
>
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>


Hello Andreas,

Try passing amd_iommu=on to the kernel and test it yourself and tell us as
well.

Regards,
Iosif
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