Re: [Xen-devel] xen EFI boot and vga-passthrough

[Laszlo Ersek <lersek@xxxxxxxxxx>]

On 11/12/12 20:08, Kristian Hagsted Rasmussen wrote:
> Hi all
> 
> I can't seem to find any information on vga-passthrough when booting
> through xen.efi, so I assume it should work. But I encounter a problem
> on a windows 7 HVM that boots fine when dom0 is booted through MBR but
> fails when dom0 is booted through UEFI.
> 
> My system is:
> DQ77KB motherboard with bios version 44
> Core i7-3779T with VT-d
> Intel HD graphics 4000
> 
> In the qemu log it seem like xen cannot reach the vga-bios. Is this a
> known problem when booting through xen.efi or is it a bug?

The legacy VGA BIOS is not present on UEFI platforms unless an
(optional) compatibility support module provides it. (Tangentially,
Secure Boot disables CSMs.)

Windows 7 / Windows 2008 R2 have a bug: even when booted on an UEFI
platform, they depend on the optional VGA BIOS unconditionally. This
seems to have been fixed in Windows 8 / Windows Server 2012.

See <http://www.linux-kvm.org/page/OVMF#Windows_Server_2008_R2_SP1>
and/or the long "OVMF + Windows 2008 r2 sp1" thread on edk2-devel.

(Apologies if I misunderstood your question. Admittedly, I haven't done
any homework wrt. xen.efi or vga passthrough. But your email had too
many keywords to push my buttons.)

Laszlo

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