On 09/16/16 08:28, Martin Kletzander wrote:
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@redhat.com> Cc: Drew Jones <drjones@redhat.com> Cc: Marc-André Lureau <marcandre.lureau@redhat.com> Suggested-by: Marc-André Lureau <marcandre.lureau@redhat.com> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1372901 Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Very nicely written, makes sense and since virtio-vga didn't work for virt machines, there is no problem with changing it.
Thank you!
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:
While working on the test data, I consulted other files, and I noticed that they were carefully wrapped. I tried to do the same -- did I fail? $ wc -L \ tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args 74 tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args and "tests/test-wrap-argv.pl" has my $max_len = 78; Hmmm... After running the script, it looks like I was too cautious. The problem is actually that I broke one of those lines too early, and now it's too short. :) I'll send a v2. Thanks! Laszlo
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@redhat.com>