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

["David Stone" <unclestoner@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)

Hmm...why can't I just leave the Cirrus emulated card as it is?  The
Windows DomU would continue to see it and us it as the primary display
device.  I've already verified that I can hide the real graphics card
from Dom0 and this works fine...there is not output from Dom0 or any
DomU of course, but can connect to DomU via the serial port or ssh,
and I can connect to Windows DomU via RDP.

The idea is that the real PCI Express graphics card that is passed
through to Windows DomU would appear to the Windows OS as a
_secondary_ display display device.  If one has a bare-metal OS with
two graphics adapters, I assume only one of them (the "primary") is
responsible for stuff like the VGA BIOS?   I just want to write
Direct3D code to cause the physical graphics card to render to an
_off-screen_ surface...not to a framebuffer.  I could then scrape the
rendered bitmaps and do whatever I wanted with them.

Thanks,
Dave

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