Troubleshoot: Video not working on virtual machines in Hyper-V

[KexyBiscuit]

Symptoms

An AOSC OS-based virtual machine experiences a blank screen or a blurred screen or gets stuck in the GRUB screen or the UEFI screen.

On virtual machines using hyperv_drm driver, xorg-server reports the following errors and warnings in /var/log/Xorg.0.log.

…
[     9.033] (WW) Falling back to old probe method for modesetting
…
[     9.033] (EE) Unable to find a valid framebuffer device
[     9.033] (WW) Falling back to old probe method for fbdev
…
[     9.034] (EE) Screen 0 deleted because of no matching config section.
…
[     9.034] (EE) Screen 1 deleted because of no matching config section.
…
[     9.034] (EE) 
Fatal server error:
[     9.034] (EE) Cannot run in framebuffer mode. Please specify busIDs        for all framebuffer devices
[     9.034] (EE) 
[     9.034] (EE) 
Please consult the The X.Org Foundation support 
	 at http://wiki.x.org
 for help. 
[     9.034] (EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.
[     9.034] (EE) 
[     9.036] (EE) Server terminated with error (1). Closing log file.

On virtual machines using hyperv_fb driver, plymouth 2:22.02.122-4 or earlier might silently fail to display the splash screen, and plymouth 2:24.004.60 will get stuck in the GRUB screen or the UEFI screen.

Cause

This problem occurs because xorg-server before 21.1.13-2 doesn't support hyperv_drm driver, and plymouth doesn't support hyperv_fb driver.

Resolution

To resolve the issue with hyperv_drm driver, update xorg-server to 21.1.13-2 or later.

The issue with hyperv_fb driver won't be fully fixed, since it's already replaced by hyperv_drm driver. To remove hyperv_fb driver, update linux+kernel to 3:6.10.2 or later, linux+kernel+lts to 2:6.6.48 or later.

However, since the issue rooted in plymouth, affecting frame buffer drivers other than hyperv_fb, an update has been released. Update plymouth to 2:24.004.60-1 or later should be considered as a workaround, if the kernel can't be updated, or hyperv_fb driver is still required.

Note that even with the latest plymouth, the splash screen might still not be displayed on virtual machines using hyperv_fb driver, but no other side effect should be observed.

More Information

Red Hat purposed a mustard for the issue with hyperv_drm driver in Red Hat Bugzilla – Bug 2000921, disabling the PCI probe path in xfree86. Later, xorg/xserver merged a more specific patch to accept devices with the 'hyperv_drm' driver in xfree86. xorg-server 21.1.13-2 includes the latter patch.

hyperv_fb driver was replaced by hyperv_drm driver in the Microsoft Azure flavor of Linux Kernel in Ubuntu, requested by Microsoft, so any issue related to this driver will be a wontfix.

The issue with plymouth was introduced in 23.356.9 upstream, and the fix was merged recently. plymouth 2:24.004.60-1 includes the fix.

Status

xorg-server: 21.1.13-2 shipped to stable in #7847.
linux+kernel: 3:6.10.2 shipped to stable in #7490.
linux+kernel+lts: 2:6.6.48 being tested in #7848.
plymouth: 2:24.004.60-1 being tested in #7864.

Acknowledgements

@lunzima provided insights on this issue in #7832.
@Icenowy and @KexyBiscuit picked the final patches.
@MingcongBai provided more insights on the issue with plymouth.

[KexyBiscuit]

Updated information about the issue with plymouth.