Re: [Xen-devel] Windows 8 VGA Passthrough

[Gordan Bobic <gordan@xxxxxxxxxx>]

I'd focus more on why exactly do you think you need primary passthrough. 
Is your requirement for seeing the SeaBIOS POST and the Windows loading 
animation strong enough to bother with the amount of extra pain that it 
is going to require?
On 10/28/2013 08:31 PM, John Wargo wrote:
> This sounds about right, what then is the fix though? How do i get
> qemu/hvm load the right vbios? On a side note, I assume that i need to
> install the mentioned patch, if so, whats the best way to apply it? (It
> seems dated, and i get errors when i try to patch with it)
>
> Sorry for asking such basic questions,
> -John
>
> On Monday, October 28, 2013, Zytaruk, Kelly <Kelly.Zytaruk@xxxxxxx
> <mailto:Kelly.Zytaruk@xxxxxxx>> wrote:
>  > On Sunday, October 27, 2013 1:21 PM, John Wargo wrote:
>  >>I've made quite a bit of changes since my last email, and so far
> here's what I've got:
>  >>
>  >>AMD FX6300
>  >>ASUS M5A99X evo r2.0
>  >>ASUS Radeon 6670 (Dom0)
>  >>XFX Radeon 7850 (Win8)
>  >>
>  >>...
>  >>
>  >>Is there some sort of AMD Radeon patch I need to use (I saw one on
> the wiki, but it appeared to be several years old), or is it a needed
> configuration?
>  >>
>  >>Thanks for your time,
>  >>-John
>  >
>  > Hi John,
>  >
>  > I am using XEN4.2 with QEMU-traditional and I have identified a
> couple of issues in regards to passing through a video adapter as the
> primary (VGA enabled) adapter.
>  >
>  > The patch that you referenced attempts to get around one of the
> issues but it is not complete and doesn't cover all of the cases.  If
> you apply the patch it will definitely help but not guaranteed to fix
> all of your problems.
>  >
>  > The second issue is related to the fact that you are using two
> different graphics adapters.  I am assuming that the Radeon 6670 is the
> primary (boot/VGA) adapter and that the 7850 is the secondary.
>  >
>  > From reading your thread I assume that you want to pass the 7850
> through to the DomU as the primary.  I have been able to do this
> successfully with a few fixes.   The problem is in the way
> QEMU/hvmloader handle the VBios code.  When you boot with the 6670 as
> the primary the VBios code for the graphics adapter is copied to memory
> at address 0xc0000.  When QEMU passes the 7850 through to the DomU it
> copies VBios from 0xc0000 in Dom0 memory space into 0xc0000 in DomU
> memory space.  DomU is effectively executing the VBios for the wrong
> video card.  The correct fix is to have the hvmloader read a fresh copy
> of VBios from the 7850 and copy it into the DomU address space at 0xc0000.
>  >
>  > Sometimes you can get away with executing the wrong VBios, sometimes
> you get stung.
>  >
>  > Hope the explanation helps,
>  > Kelly
>  >
>  >
>  >

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