[libvirt] [PATCH] qemu: use 'bochs' video type by default for UEFI domains

[Daniel P. Berrangé]

On Thu, Aug 29, 2019 at 12:19:49PM +0200, Gerd Hoffmann wrote:
>   Hi,
> 
> > Incidentally, and I haven't followed this closely so apologies if I'm
> > asking a silly question, if the point of bochs-display is to have a
> > video device without legacy VGA emulation then why aren't we using
> > the existing virtio-gpu, which has been around a lot longer and has
> > better support throughout the stack, instead?
> 
> Well, virtio-gpu (on x86) actually is "-device virtio-vga".  That comes
> with legacy VGA emulation, for the boot display ...
> 
> For UEFI guests with virtio-gpu support it is possible to use "-display
> virtio-gpu-pci" instead (simliar to arm).  Only drawback is that you
> can't have a EFI GOB with virtio-gpu-pci, so efifb doesn't work.  Linux
> kernel console shows up after the virtio-gpu driver loads, which is
> rather late compared to efifb.
> 
> For UEFI guests without virtio-gpu support "-device virtio-gpu-pci" will
> not work due to the lack of EFI GOB support.  For these guests
> "-display bochs-display" should preferred over "-device VGA", to get rid
> of the unused legacy VGA emulation (and thereby reduce the attack
> surface).
> 
> Also note that bochs-display can be plugged into pcie slots (that is
> true for virtio-gpu-pci too btw).

BTW a while ago you did a really helpful blog post describing best usage
for each display type

  https://www.kraxel.org/blog/2014/10/qemu-using-cirrus-considered-harmful/

there's been quite a few changes since then with virtio-vga and bochs-display
arriving, so it would be awesome if you wrote an updated blog post, or even
added something to the main qemu-doc.texi doc giving recommandations for what
to use for guests. 


Regards,
Daniel
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