Re: [Xen-devel] Determining iommu groups in Xen?

[Peter Kay <syllopsium@xxxxxxxxxxxxxxxx>]

On 28 August 2014 19:02:47 BST, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>On 28/08/14 18:53, Peter Kay wrote:
>>
>> On 28 August 2014 18:13:07 BST, Andrew Cooper
><andrew.cooper3@xxxxxxxxxx> wrote:

>> An iommu group, as far as I'm aware, is the group of devices that are
>not protected from each other. In KVM, you must pass through the entire
>group to a VM at once, unless a 'don't go crying to me if it stomps
>over your memory space or worse' patch is applied to the kennel
>claiming that everything is fine.
>
>I have googled the term in the meantime, and it is what I initially
>thought.
>
>All PCI devices passed though to the same domain share the same single
>"iommu group" per Kernel/KVM terminology.  There is not currently any
>support for multiple iommu contexts within a single VM.
>
>~Andrew
No, it's not that. The iommu group relates to the root port above the devices.

I can say from experience it's perfectly acceptable to have multiple iommu 
groups assigned to one VM in both Xen and KVM. Usually I have a PCIe graphics 
card (attached to a PCIe root so in its own group) and three PCI cards on a PCI 
segment which IIRC is attached to a PCIe to PCI bridge via a PCIe root, in 
another group. They're all ultimately hanging off the ICH9R PCH, but that 
shouldn't matter.

I'll see if I can find a more definitive explanation in a bit

PK
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

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