Re: [Xen-devel] questions about xen device pass-through.

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Tue, Aug 23, 2011 at 06:02:49PM -0400, Dushmanta Mohapatra wrote:
>    Thanks Jean.I got it resolved.
> 
>    But now I am facing an issue at the next step. After I assign the device
>    back to Dom0,
>    there is an issue in DomU reverting back to the virtual mode.
> 
>    Initially I start an Windows 7 HVM DomU and give it virtualized access to
>    various devices.
>    After that I unbind some devices (Ethernet in this case), assign them to
>    pciback  and attach them to DomU (using xm pci-attach). At this stage DomU
>    recognizes the hotplugging and I get passthrough IO. Afterwards I detach
>    the device from DomU (using xm pci-detach). At this stage the device gets
>    assigned to pciback. So I unbind it from pciback and bind the device back
>    to Dom0 using sysfs mechanisms. So Dom0 gets direct access to the device.
>    Dom0 network works fine after this.
> 
>    But after this DomU does not revert back to the virtual interface it was
>    using earlier. In case of ethernet, I can still see a vif1.0 interface if
>    I do a ifconfig in Dom0. But there is no network access in DomU. I tried
>    to reconfigure the network/connection etc. inside Windows7 DomU, but could
>    not get it working.
> 
>    Please tell me I am missing some thing or should be doing it some other
>    way.
>    Let me know if I need to give some more information.
> 

Did you check if the vif is still attached to the bridge? 
(brctl show)

And I guess this was a different NIC than what's used in the bridge?

-- Pasi

>    (I am just testing for ethernet right now..I am planning to try this for
>    other kinds of devices also like VGA,USB, Wireless etc.)
> 
>    Thanks,
>    Dushmanta
> 
>    On Wed, Aug 17, 2011 at 6:27 PM, Jean Guyader <[1]jean.guyader@xxxxxxxxx>
>    wrote:
> 
>      On 17 August 2011 20:55, Dushmanta Mohapatra
>      <[2]dushmanta.mohapatra@xxxxxxxxx> wrote:
>      > Hello,
>      >
>      > I have some doubts/questions regarding device passthrough support in
>      Xen.
>      > I will really appreciate some help/suggestions.
>      >
>      > (I am using a Intel Core i5 vPro based Lenovo thinkpad T520 (Intel
>      graphics
>      > adapter).
>      > I am running Xen 4.1.1 and PVOPS based Linux 2.6.32.41 kernel as Dom0.
>      I use
>      > Windows XP
>      > and Windows 7 as my HVM Domus. lspci details are attached.)
>      >
>      > I am trying to achieve the following: Initially allow
>      > direct access to the primary devices (graphics/ethernet/wireless/USB)
>      to an
>      > HVM DomU. After wards,
>      > depending on the need I want to re-assign the direct access of these
>      devices
>      > back to Dom0 and
>      > have the DomU access the devices in a virtual manner.
>      >
>      > So my question is: Is it possible to do it? Is it possible for VGA/
>      > graphics?
>      >
>      > I have tried a few things and following is what I am being able to do:
>      >
>      > I am being able to provide direct access to devices
>      > (wireless/ethernet/graphics etc) to HVM DomUs.
>      > And also I am being able to dynamically change the direct access to
>      these
>      > devices between
>      > the various HVM DomUs (tested with WinXP and Windows 7) in case of
>      > ethernet/USB etc. I am being
>      > able to detach it from one DomU and attach it to another. (This is not
>      > working with VGA direct access
>      > though.)
>      >
>      > But I am not being able to reattach these devices back to Dom0. I have
>      tried
>      > the sysfs way and initial
>      > boot time passthrough.
>      >
>      > I have also tried the stubdomain way, but when I do not hide the
>      devices
>      > from Dom0 (at boot time) and later try to assign them to stubdomain,
>      my Dom0
>      > gets rebooted automatically. I am following
>      > the steps mentioned in:
>      > [3]http://mirror.choon.net/xen/xen-unstable.hg/docs/misc/vtd.txt
>      >
>      > So could some one  tell me if these behaviors are expected or
>      > if I might be doing something wrong.
>      >
>      > I will really appreciate any help. Please let me know if more
>      information is
>      > needed from my side.
>      >
> 
>      Hi,
> 
>      If you detach a pass through device from a domU it gets reassigned to
>      dom0 automatically.
>      The problem you are having is that pciback in dom0 still own the
>      device that why it looks like
>      the device isn't working in dom0.
> 
>      You'll have to manually unbind the device from picback and bind it to
>      another driver in dom0.
>      That can be done through the sysfs driver nodes "bind" and "unbind".
>      Jean
> 
> References
> 
>    Visible links
>    1. mailto:jean.guyader@xxxxxxxxx
>    2. mailto:dushmanta.mohapatra@xxxxxxxxx
>    3. http://mirror.choon.net/xen/xen-unstable.hg/docs/misc/vtd.txt

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