[libvirt] [Qemu-devel] [PULL v3 00/54] Kconfig conversion, excluding ARM and MIPS

[Laszlo Ersek]

On 03/21/19 18:58, Peter Maydell wrote:
> On Thu, 21 Mar 2019 at 17:35, Laszlo Ersek <lersek at redhat.com> wrote:
>> It simply keeps the status quo from before the patchset.
>>
>> The specific emulation targets that virtio-vga should not be enabled for
>> (regardless of other targets / machine types) are arm/aarch64. IOW, in
>> the longer term, it's not that virtio-vga is suitable only for PC ||
>> DINO || PSERIES, but that it's *not* suitable for arm/aarch64.
> 
> Relying on the device not being present for aarch64 seems
> fragile to me. It will break if we add a different
> aarch64 machine other than "virt" and want that other
> machine to have virtio-vga. It will also break if we
> ever manage to get full heterogenous-CPU support and
> end up with a single qemu-system binary that can emulate
> both AArch64 virt and x86-64 pc machines :-)
> 
> If what you want is "don't use virtio-vga when using KVM
> on aarch64" then why not have logic that implements that?

That's actually the logic that I implemented originally (or something very close to it -- <https://libvirt.org/git/?p=libvirt.git;a=commitdiff;h=706b5b627719e95a33606c463bc83c841c7b5b0e>), but since then, this code has been modified in libvirt multiple times:

* [libvirt] [PATCH v2 00/17] cleanups and improvements for video device code
  https://www.redhat.com/archives/libvir-list/2016-October/msg00533.html
  https://libvirt.org/git/?p=libvirt.git;a=shortlog;hp=a62655f9c33a8f7c6257779ddbdbf1352d53a526;h=fb8f3b1c22c8f272bb9a47e8f8915acc3cfb47f1

* [libvirt] [PATCH v3 0/6] Add support for video and input devices on S390
  https://www.redhat.com/archives/libvir-list/2018-March/msg01519.html
  https://libvirt.org/git/?p=libvirt.git;a=commitdiff;h=4bbf7f8cb5bf979ea2f5c247b2ddb884a07ac33f

I'm not implying that those patches must have introduced a libvirt regression, I just agree that the code deserves investigation. This is why I added libvir-list to the CC list when reporting the problem.

> For 4.0 we should definitely just retain what we had
> before the introduction of KConfig, but as a general
> thing we should look to not have to have this odd
> wrinkle.
> 
> (AFAIK virtio-vga is no different in this regard to the other
> vga PCI devices, which also won't work in KVM setups.)

I agree -- please refer to the "domcapabilities" part (1) of my report:

https://lists.gnu.org/archive/html/qemu-devel/2019-03/msg06060.html

> @@ -92,6 +92,8 @@
>      <video supported='yes'>
>        <enum name='modelType'>
>          <value>vga</value>
> +        <value>cirrus</value>
> +        <value>vmvga</value>
>          <value>virtio</value>
>        </enum>
>      </video>

"cirrus" and "vmvga" look wrong for aarch64.

Thanks
Laszlo