[Bug] virtio-gpu broken with qemu/kvm on arm64 on kernel 5.5+

[Guillaume Gardet]

Hi,

> -----Original Message-----
> From: Chia-I Wu <olvaffe at gmail.com>
> Sent: 20 February 2020 19:41
> To: Guillaume Gardet <Guillaume.Gardet at arm.com>
> Cc: dri-devel at lists.freedesktop.org; Gerd Hoffmann <kraxel at redhat.com>;
> Daniel Vetter <daniel.vetter at ffwll.ch>; Catalin Marinas
> <Catalin.Marinas at arm.com>; nd <nd at arm.com>
> Subject: Re: [Bug] virtio-gpu broken with qemu/kvm on arm64 on kernel 5.5+
> 
> On Thu, Feb 20, 2020 at 4:44 AM Guillaume Gardet <Guillaume.Gardet at arm.com>
> wrote:
> >
> > Hi,
> >
> > With (guest) kernel 5.5+ with qemu/kvm on arm64, I get lots of display
> corruptions leading to this kind of screen:
> > https://openqa.opensuse.org/tests/1174521#step/yast2_i/24
> Looking at the screenshot, it seems cacheline-related?

It could be.

> 
> There was a change of memory type
> 
>   https://lists.freedesktop.org/archives/dri-devel/2019-August/233456.html
> 
> While the guest memory type is ignored on Intel, it is honored on ARM.
> This attempt to fix it
> 
>   https://lists.freedesktop.org/archives/dri-devel/2019-December/248271.html
> 
> does not seem to land.

I applied this patch on top of 5.5.4, but it does not fix the problem.
Maybe more similar changes are required?

Regards,
Guillaume

> 
> 
> >
> > I git bisected it to commit c66df701e783bc666593e6e665f13670760883ee
> > **********
> > drm/virtio: switch from ttm to gem shmem helpers
> >
> >   virtio-gpu basically needs a sg_table for the bo, to tell the host where
> >   the backing pages for the object are.  So the gem shmem helpers are a
> >   perfect fit.  Some drm_gem_object_funcs need thin wrappers to update the
> >   host state, but otherwise the helpers handle everything just fine.
> >
> >   Once the fencing was sorted the switch was surprisingly easy and for the
> >   most part just removing the ttm code.
> >
> >   v4: fix drm_gem_object_funcs name.
> >
> >   Signed-off-by: Gerd Hoffmann <kraxel at redhat.com>
> >   Acked-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> >   Reviewed-by: Chia-I Wu <olvaffe at gmail.com>
> >   Link:
> > http://patchwork.freedesktop.org/patch/msgid/20190829103301.3539-15-kr
> > axel at redhat.com
> > **********
> >
> > I also tested kernel 5.6-rc2 which has the same bug.
> > Without kvm, the display is fine.
> >
> > Regards,
> > Guillaume
> >