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

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 02/03/15 14:25, Konrad Rzeszutek Wilk wrote:
> 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.

That's even worse.  Please just fix your toolstack to not create the vfb
backend if you don't want to use it.

David

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