Re: [Xen-devel] Regression due to d9581c7dcac15c02ad4d47c60c60f4d8f197db55 en/fb: allow xenfb initialization for hvm guest

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 27/02/15 21:24, Konrad Rzeszutek Wilk wrote:
> This has been in queue for some time.
> 
> In our kernels (UEK3) we had to revert said patch. The patch says:
> 
> "    xen/fb: allow xenfb initialization for hvm guests
> 
>     There is no reasons why an HVM guest shouldn't be allowed to use xenfb.
>     As a matter of fact ARM guests, HVM from Linux POV, can use xenfb.
>     Given that no Xen toolstacks configure a xenfb backend for x86 HVM
>     guests, they are not affected.
> 
>     Please note that at this time QEMU needs few outstanding fixes to
>     provide xenfb on ARM:
> 
>     http://marc.info/?l=qemu-devel&m=138739419700837&w=2
> "
> 
> which is a lie. The "no Xen toolstacks configure a xenfb backend for
> x86 HVM" is actually a lie. If you try to boot this kernel under
> Xen with Xend it will be a problem - as Xend does setup an 'vfb'
> device.
> 
> The end result is that during the bootup - up until X starts, there is
> no console output on the VNC window. As the Linux kernel tries to use
> the vfb console driver.

This looks like a toolstack bug to me.  If the toolstack has configured
a vfb backend surely that should be preferred to the emulated VGA?

> Any suggestsion on how to fix this? Should we just wrap the
> whole thing with #ifdef, like this?

No.  We want to avoid frontend drivers behaving differently on different
architectures.

David

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