RE: [Xen-devel] Using VT-D to grant a Windows DomU access to aPCIExpress graphics card?

["Han, Weidong" <weidong.han@xxxxxxxxx>]

Graphics card assignment is complex, and not easy to implement. I am not
an expert on it, I can tell you some things I know. 
By default, cirrus VGA is emulated for guest. If using VT-d to directly
assign graphics card to guest, first should remove some cirrus VGA
stuffs. It should need 1:1 mapping of frame buffer, VGA bios and VGA
standard I/O ports, and permit directly access right to them. In
addition, you may also need replace guest int10 and int42 handlers with
host handlers. At last, if graphics card's memory is close to or bigger
than 256M, should enlarge guest e820 mmio size, because current guest
mmio size is 256M. 

Randy (Weidong)

David Stone wrote:
>>>> Graphices card is special. Many tricky things need to be done, such
>>>> as frame buffer, VGA guest bios, etc. So current VT-d in Xen
>>>> doesn't support assigning graphics card yet.
>>> 
>>> I wonder if those complications (which I don't pretend to
>>> understand) would go away if the graphics card did not have to
>>> produce any output to a locally attached monitor?  My goal is not
>>> to render the Windows DomU graphics to the local monitor, but
>>> rather to just use the graphics device to do work like rendering to
>>> an off-screen buffer.  I can then do whatever I want with that
>>> buffer, such as send it over the network to another machine for
>>> display.  The Windows DomU would be running completely headless...I
>>> can RDP into it to administer it. 
>>> 
>>> Would that make it more feasible?
>>> 
>> 
>> I don't think so. Without those complications, graphics card even
>> can't work on guest. I think displaying on local monitor is the same
>> with displaying on remote machine in essence.
> 
> OK.  I wonder if you could you give me a brief description of these
> complications (why they are a problem, and what needs to be done in
> the Xen source to handle them)?
> 
> Thanks,
> Dave
> 
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