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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Mar 02, 2015 at 10:47:12AM +0000, David Vrabel wrote:
> 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?

This is Xend. It is a bit brain dead in this category.

> 
> > 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.

We could try detecting that it is Xend (not sure how?) - or that it is
Xen 4.4 or below - which would be the only versions that could be run with
Xend.
> 
> David

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