RE: [Xen-users] Graphic Card on DomU (windows)

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> oni.meno.kyo@xxxxxxx
> Sent: 30 May 2006 09:05
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-users] Graphic Card on DomU (windows)
> 
> Hi to all,
> 
> I would like to use a dedicated video card in a Windows domU. 
> I know this subject has been often under study.
> I know we can hide a e-pci card since xen 3.0.2 from dom0 to 
> a domU => Only domU could have access to the video card.
> I also know it's not possible to use such a dedicated video 
> card because as the domU (windows) is not xen-aware it will 
> send a wrong memory address to the video card to read/write.
> Here is my question : Why can't we decide which part of the 
> Ram memory dom0/domU is using?
> We could say to domU let's use 0-512Mb, dom0 let's use 
> 512-1024Mb for example.
> So that the domU will say to the video card to read 327Mb 
> information which is in fact really 327Mb. So that the video 
> card should work isn't it?
> 
> Is that kind of thing an impossible solution to wait until IOMMU?

Theoretically that would be possible, but it would mean that we'd have
to REMAP the kernel loaded by GRUB (or whatever bootloader you use to
load Xen and Dom0), since those are loaded before Xen has been given
control -> xen can't decide where itself is being loaded to... 

I'm not sure it's an important enough problem for someone to solve tho'.
It may be trivial (I haven't actually looked at it), but it would at
least require:
1. A change to the configuration of Dom0 and Xen itself, and add some
manual configuration to indicate which DomU gets the low memory that was
freed up by moving Xen/Dom0 up in memory.
2. Modifying some of the initial page-table setup and adding code in
(probably both of) Xen and/or the Dom0 Linux code to move itself to a
different address.
There would also need to be some code to figure out if you attempt to
load TWO different DomU's at the low address... :-)
3. Adding some documentation of how to configure/control this. 

As I said, I haven't even looked at the code for this, so I don't know
if it's a two-line hack or a major overhaul. If you fancy hacking on it,
I'm sure the guys at XenSource would at least consider a patch.

--
Mats

> 
> Thanks in advance for your answers...
> 
> PS : Sorry for my poor english...^^
> 
> 
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