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Re: [Xen-devel] Xen on ARM basic questions

Hi Ian,

Sorry for the delayed response. I was struggling with some dom0 crashes when
i migrated to v3.12 based kernel.

On Tue, Nov 19, 2013 at 6:20 AM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Mon, 2013-11-18 at 13:57 -0500, Vaibhav Bedia wrote:
>> Hi,
>> I have a couple of basic questions regarding the Xen on ARM (with
>> virtualization extensions). It probably falls under WIP but i thought
>> i'll ask anyway.
>> 1. Using the current unstable Xen on ARM code is it possible to
>> virtualize network, usb, sata and things like that? I looked at the
>> wiki pages for Arndale, VExpress but could not figure out whether this
>> is supported right now. If not, are there any patches that i can
>> try out?
> Xen on ARM does not expose real USB/SATA/network etc to the guests/domU.
> All of the physical devices are exposed only to dom0 which in turn
> provides "paravirtualised" virtual devices for disk, network and console
> which are exposed to the guest.
> There is currently no PV usb for Xen on ARM, although there is some work
> ongoing on x86 which may be reuseable.
> Eventually we will also support physical device passthrough which would
> allow you to dedicate each device (USB controller, SATA controller, NIC
> etc) to a single guest.

Ok. Thanks for the clarification.

>>  After going through the recent talk from Stefano [1] i got
>> the impression getting network and SATA requires SWIOTLB support. Is
>> that correct?
> The SWIOTLB or an IOMMU/SMMU is necessary for dom0 to drive the physical
> devices and provide the virtual interfaces to the guests.
> Device passthrough will only be supported with an IOMMU/SMMU.

So on SoCs like OMAP5 which don't have an IOMMU device passthrough won't be
supported? Or it can be done via SWIOTLB if someone works on it?

>> 2. For domU to see the network and SATA interfaces is the DTB supposed
>> to be updated? Is there some guideline on how to do this? Do i just
>> add in the nodes similar to dom0?
> Hopefully the above has made this question moot.


>> Right now i have an OMAP5 dom0 with network+usb support and i am
>> trying to figure out how to get these things in domU and hence the
>> questions.
> You need blkback and netback in dom0 and blkfront and netfront in domU
> (all in mainline Linux). Then you need to add vif and disk options to
> your guest configuration.

I enabled both of the options and can get a ramdisk based domU running fine.
I tried a Ubuntu based fs for domU but can't get to the login prompt
for some reason.
I tried out the various options mentioned @
and some other things mentioned on various forums but nothing seems to work :(
Any hints on where things could be going wrong? I have hvc0.conf under

On the networking front, i setup the brigde in dom0 and verified that i can ping
external hosts. However there's some issue with the whole thing since domU
can get an ip address but still can't ping the outside world. Switching back to
dom0 the network seems to eventually die and at times dom0 becomes totally
unresponsive :(


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