[Bug 1872863] Re: QEMU/KVM display is garbled when booting from kernel EFI stub due to missing bochs-drm module

Sun May 10 23:24:57 UTC 2020

I went and looked at the autopkgtest regressions, and they aren't actual
regressions, just transient network problems and slow build timeouts.

chrony autopkgtest regression on armhf:

Need to get 263 kB of archives.
After this operation, 2,048 B of additional disk space will be used.
Err:1 http://ftpmaster.internal/ubuntu bionic-proposed/main armhf kmod armhf 24-1ubuntu3.4
  Could not connect to ftpmaster.internal:80 (91.189.89.99), connection timed out
Err:2 http://ftpmaster.internal/ubuntu bionic-proposed/main armhf libkmod2 armhf 24-1ubuntu3.4
  Unable to connect to ftpmaster.internal:http:

Network problems for this one.

All the linux packages for arm64:

autopkgtest [15:44:38]: ERROR: timed out on command /tmp/autopkgtest.M7KUyX/build.f2S/src/debian/tests/rebuild
autopkgtest [15:48:48]: test rebuild: -----------------------]
rebuild              FAIL timed out

Slow builds for these packages. Maybe the arm64 build host was having a
bad day.

I think the autopkgtests just need to be re-run.

-- 
You received this bug notification because you are a member of Ubuntu
Foundations Bugs, which is subscribed to kmod in Ubuntu.
https://bugs.launchpad.net/bugs/1872863

Title:
  QEMU/KVM display is garbled when booting from kernel EFI stub due to
  missing bochs-drm module

Status in kmod package in Ubuntu:
  Fix Released
Status in linux package in Ubuntu:
  Fix Released
Status in kmod source package in Bionic:
  Fix Committed
Status in linux source package in Bionic:
  Fix Committed

Bug description:
  BugLink: https://bugs.launchpad.net/bugs/1872863

  [Impact]

  A recent grub2 SRU, LP #1864533, now forces the kernel to boot via the
  kernel EFI stub whenever EFI is enabled. This causes problems for
  QEMU/KVM virtual machines which use the VGA=std video device, as the
  efifb driver yields an unreadable garbled screen. See the attached
  image.

  The correct framebuffer driver to use in this situation is bochs-drm,
  and modprobing it from a HWE kernel fixes the issues.

  bochs-drm is missing from Bionic since CONFIG_DRM_BOCHS was disabled
  in LP #1378648 due to bochs-drm causing problems in a PowerKVM
  machine. This problem appears to be fixed now, and bochs-drm has been
  re-enabled for Disco and up, in LP #1795857 and has been proven safe.

  This has also come up again in LP #1823152, as well as chatter on LP
  #1795857 to get this enabled on Bionic.

  The customer which is experiencing this issue cannot switch to VGA=qxl
  as a workaround, and must use VGA=std, hence I suggest we re-enable
  bochs-drm for Bionic.

  [Fix]

  I noticed on Focal, if you boot, the framebuffer is initially efifb:

  [ 0.603716] efifb: probing for efifb
  [ 0.603733] efifb: framebuffer at 0xc0000000, using 1876k, total 1875k
  [ 0.603735] efifb: mode is 800x600x32, linelength=3200, pages=1
  [ 0.603736] efifb: scrolling: redraw
  [ 0.603738] efifb: Truecolor: size=8:8:8:8, shift=24:16:8:0
  [ 0.604462] Console: switching to colour frame buffer device 100x37
  [ 0.605829] fb0: EFI VGA frame buffer device

  This soon changes to bochs-drm about a second later:

  [ 0.935988] bochs-drm 0000:00:01.0: remove_conflicting_pci_framebuffers: bar 0: 0xc0000000 -> 0xc0ffffff
  [ 0.937023] bochs-drm 0000:00:01.0: remove_conflicting_pci_framebuffers: bar 2: 0xc1c8c000 -> 0xc1c8cfff
  [ 0.937776] checking generic (c0000000 1d5000) vs hw (c0000000 1000000)
  [ 0.937776] fb0: switching to bochsdrmfb from EFI VGA
  [ 0.939085] Console: switching to colour dummy device 80x25
  [ 0.939117] bochs-drm 0000:00:01.0: vgaarb: deactivate vga console
  [ 0.939210] [drm] Found bochs VGA, ID 0xb0c5.
  [ 0.939212] [drm] Framebuffer size 16384 kB @ 0xc0000000, mmio @ 0xc1c8c000.
  [ 0.941955] lpc_ich 0000:00:1f.0: I/O space for GPIO uninitialized
  [ 0.942069] [TTM] Zone kernel: Available graphics memory: 2006780 KiB
  [ 0.942081] [TTM] Initializing pool allocator
  [ 0.942089] [TTM] Initializing DMA pool allocator
  [ 0.943026] virtio_blk virtio2: [vda] 20971520 512-byte logical blocks (10.7 GB/10.0 GiB)
  [ 0.944019] [drm] Found EDID data blob.
  [ 0.944162] [drm] Initialized bochs-drm 1.0.0 20130925 for 0000:00:01.0 on minor 0
  [ 0.944979] fbcon: bochs-drmdrmfb (fb0) is primary device
  [ 0.947712] Console: switching to colour frame buffer device 128x48

  On bionic, the framebuffer never changes from efifb, since the bochs-
  drm kernel module is not built, and it is also present on the module
  banlist in /etc/modprobe.d/blacklist-framebuffer.conf

  bochs-drm needs to be enabled to be built in the kernel config, and
  removed from the module blacklist in kmod.

  [Testcase]

  Create a new QEMU/KVM virtual machine, I used virt-manager. Before you
  install the OS, check the box to modify settings before install. In
  the "Overview" tab, enable EFI by setting the firmware to "UEFI
  x86_64: /usr/share/OVMF/OVMF_CODE.secboot.fd".

  Set the video device to qxl while you install Bionic. Once the install
  is done, reboot, do a "apt update" and "apt upgrade", to ensure you
  have grub2 2.02-2ubuntu8.15 installed.

  Shut the VM down, and set the video device to VGA. Or VGA=std if you
  use the QEMU command line.

  Start the VM up, and the screen will be garbled. See attached picture.

  If you install my test packages, which are available here:

  https://launchpad.net/~mruffell/+archive/ubuntu/sf272653-test

  Instructions to install (on a bionic system):

  1) Enable bionic-proposed
  2) sudo apt-get update
  3) sudo apt install linux-image-unsigned-4.15.0-96-generic linux-modules-4.15.0-96-generic linux-modules-extra-4.15.0-96-generic linux-headers-4.15.0-96-generic linux-headers-4.15.0-96 libkmod2 kmod
  4) sudo reboot
  5) uname -rv
  4.15.0-96-generic #97+TEST272653v20200409b1-Ubuntu SMP Thu Apr 9 04:09:18 UTC 2020

  If you reboot, the screen will be perfectly readable, since the bochs-
  drm driver will be in use.

  [Regression Potential]

  We are enabling a display driver on Bionic which was previously
  disabled, so there will be some virtual machines making the jump to
  using bochs-drm since it would now be available.

  I don't think that this is a bad thing, and in many ways will probably
  end up improving some user's experience. Although there are two
  scenarios where a regression could happen:

  1 - frequently gamers use GPU passthrough to their kvm based virtual
  machines, and I have seen them expect, or hardcode their kernel
  command lines to disable the efifb driver. See
  https://passthroughpo.st/explaining-csm-efifboff-setting-boot-gpu-
  manually/ Worst case scenario, gamers will also need to disable bochs-
  drm as well. Since the PCI device of the GPU is being passed through
  to the VM, I believe the kernel will make the correct choice and load
  the GPU drivers, like noverau or nvidia-drm instead.

  2 - if the bug with PowerKVM machines isn't actually fixed in Bionic,
  it will cause a regression on POWER. We just need to test this on
  POWER and ensure that the bug in LP #1378648 was fixed. If not, then
  we could just disable bochs-drm on POWER, leaving it enabled for all
  other archs.

  Note: 2 has now been tested and verified working. See comment #7.

  If a regression were to occur, it would only affect KVM machines that
  use the built in SPICE graphics display. The screen would either not
  show at all or be garbled. bochs-drm is limited only to kvm users, and
  does not affect other virtualisation platforms like VMware or
  Virtualbox. Instances will still be accessible via ssh, and work
  normally.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/kmod/+bug/1872863/+subscriptions