Re: [Xen-devel] gfx-passthrough conflict with pxe booting?

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, Aug 07, 2013 at 06:12:57PM +0800, G.R. wrote:
> A quick update about the root cause of this issue:
> The rombios BIOS used in xen restrict itself to i440FX emulated by Bochs / 
> qemu.
> With gfx-passthrough, the pci-host bridge in the domU is replaced by
> the device in the host machine.
> This makes PCI emulation fail.
> The issue can be fixed by simply commenting out this line:
> 
> diff --git a/tools/firmware/rombios/rombios.c 
> b/tools/firmware/rombios/rombios.c
> index 80980b6..e9c5c4a 100644
> --- a/tools/firmware/rombios/rombios.c
> +++ b/tools/firmware/rombios/rombios.c
> @@ -220,7 +220,7 @@
>  // define this if you want to make PCIBIOS working on a specific bridge only
>  // undef enables PCIBIOS when at least one PCI device is found
>  // i440FX is emulated by Bochs and QEMU
> -#define PCI_FIXED_HOST_BRIDGE 0x12378086 ;; i440FX PCI bridge
> +//#define PCI_FIXED_HOST_BRIDGE 0x12378086 ;; i440FX PCI bridge
> 
>  // #20  is dec 20
>  // #$20 is hex 20 = 32
>

Thanks for the analysis and the workaround! 

I wonder what kind of side-effects this has (might have).. disabling the fixed 
i440FX host bridge..
I assume in your case there was no other issues introduced by the change? And 
PXE boot started working with PCI/GPU passthru.. 

-- Pasi
 
> 
> On Wed, Apr 10, 2013 at 9:54 PM, G.R. <firemeteor@xxxxxxxxxxxxxxxxxxxxx> 
> wrote:
> > Hi developers,
> >
> > I just discovered that with gfx-passthrough=1, the iPXE simply does not 
> > work.
> > It seems that no NIC is detected by iPXE -- ifstat shows nothing.
> > I'm on xen-4.2.1 release, with some IGD passthrough related patches.
> > I would like to check if this is a common issue, can anybody help?
> >
> > Thanks,
> > Timothy
> 
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