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

[Kristian Hagsted Rasmussen <kristian@xxxxxxxxxx>]

> -----Original Message-----
> From: Laszlo Ersek [mailto: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.
I will have to try to install windows 8 when I have time then.

Just compared a log file from efi boot to one from MBR boot and found this 
discrepancy between the two:
pt_register_regions: IO region registered (size=0x00400000 
base_addr=0xdfc00004) - MBR boot see last addr       0xdfc00004
pt_register_regions: IO region registered (size=0x00400000 
base_addr=0xf7000004) - EFI boot compare to MBR      0xf7000004
Can UEFI explain this discrepancy in base_addr?
It is admittedly the first portion of memory on the graphic card and is 4M in 
size, so I suspect it is the vga-bios.
And if it should not be present when boot through UEFI I will happily live with 
the error, if windows 8 can boot.
 
> 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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