Re: [libvirt] [PATCH] qemu: map "virtio" video model to "virt" machtype correctly (arm/aarch64)

On Fri, Sep 16, 2016 at 06:04:46AM +0200, Laszlo Ersek wrote: > Most of QEMU's PCI display device models, such as: > > libvirt video/model/@type QEMU -device > ------------------------- ------------ > cirrus cirrus-vga > vga VGA > qxl qxl-vga > virtio virtio-vga > > come with a linear framebuffer (sometimes called "VGA compatibility > framebuffer"). This linear framebuffer lives in one of the PCI device's > MMIO BARs, and allows guest code (primarily: firmware drivers, and > non-accelerated OS drivers) to display graphics with direct memory > access. > > Due to architectural reasons on aarch64/KVM hosts, this kind of > framebuffer doesn't / can't work in > > qemu-system-(arm|aarch64) -M virt > > machines. Cache coherency issues guarantee a corrupted / unusable > display. > The problem has been researched by several people, including kvm-arm > maintainers, and it's been decided that the best way (practically the > only > way) to have boot time graphics for such guests is to consolidate on > QEMU's "virtio-gpu-pci" device. > >> From <https://bugzilla.redhat.com/show_bug.cgi?id=1195176>;, libvirt > supports > > <devices> > <video> > <model type='virtio'/> > </video> > </devices> > > but libvirt unconditionally maps @type='virtio' to QEMU's "virtio-vga" > device model. (See the qemuBuildDeviceVideoStr() function and the > "qemuDeviceVideo" enum impl.) > > According to the above, this is not right for the "virt" machine type; > the > qemu-system-(arm|aarch64) binaries don't even recognize the "virtio-vga" > device model (justifiedly). Whereas "virtio-gpu-pci", which is a pure > virtio device without a compatibility framebuffer, is available, and > works > fine. > > (The ArmVirtQemu ("AAVMF") platform of edk2 -- that is, the UEFI firmware > for "virt" -- supports "virtio-gpu-pci", as of upstream commit > 3ef3209d3028. See > <https://tianocore.acgmultimedia.com/show_bug.cgi?id=66>.) > > Override the default mapping of "virtio", from "virtio-vga" to > "virtio-gpu-pci", if qemuDomainMachineIsVirt() evaluates to true. > > Cc: Andrea Bolognani <abologna(a)redhat.com&gt; > Cc: Drew Jones <drjones(a)redhat.com&gt; > Cc: Marc-André Lureau <marcandre.lureau(a)redhat.com&gt; > Suggested-by: Marc-André Lureau <marcandre.lureau(a)redhat.com&gt; > Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1372901 > Signed-off-by: Laszlo Ersek <lersek(a)redhat.com&gt; Very nicely written, makes sense and since virtio-vga didn't work for virt machines, there is no problem with changing it.

One small nit though, syntax-check will complain that one of the lines in the .args file is longer, you can either use 'tests/test-wrap-argv.pl --in-place tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args' or just squash this diff in, whatever you find easier:

diff --git i/tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args w/tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args index 56dbdfb66fa2..76ee977a3ca2 100644 --- i/tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args +++ w/tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args @@ -20,7 +20,7 @@ QEMU_AUDIO_DRV=none \ addr=0x1 \ -device ioh3420,port=0x9,chassis=2,id=pci.2,bus=pcie.0,multifunction=on,\ addr=0x1.0x1 \ --device virtio-net-pci,vlan=0,id=net0,mac=52:54:00:73:34:53,bus=pci.1,\ -addr=0x0,bootindex=1 \ +-device virtio-net-pci,vlan=0,id=net0,mac=52:54:00:73:34:53,bus=pci.1,addr=0x0,\ +bootindex=1 \ -net user,vlan=0,name=hostnet0 \ -device virtio-gpu-pci,id=video0,bus=pci.2,addr=0x0 -- Other than that, with that small thing fixed: Acked-by: Martin Kletzander <mkletzan(a)redhat.com&gt;