Latest linux-generic package (kernel 4.15.0-136) doesn't work on HyperV Gen2 VM

[Luis Martinez]

On Ubuntu 18.04 LTS 1&2 (so far tested), either when deploying a new VM (which pulls the latest linux-generic) or rebooting a VM (which updated the linux-generic under the cover which installs 4.15.0-136) will prevent the VM to boot.

After reboot, will get stuck on /dev/sdX: clean, x / y files, k / m blocks.

Using grub, selecting an older kernel, allow the VM to book without any issues.

I manually installed kernel 4.15.0-135, however the issue doesn't repro.

Finally I've verified that this repro on both Server 2016 and Server 2019 versions of Windows...

Output of /proc/version_signature (both on Server 2016/2019)
Ubuntu 4.15.0-29.31-generic 4.15.18

lspci -vnvn reported empty on this VM.

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1917958

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Luis Martinez (limartin84)]

Unable to run apport-collect 1917958 since the VM will not boot when selecting kernel 4.5.0-136.

[Joseph Salisbury (jsalisbury)]

It looks like a fix for this issue is already in the 137 kernel.

The change log for the -136 update shows a single change related to Hyper-V, and that change broke the ability to open /dev/fb0 and mmap it, which is what the graphic desktop will do. Running in non-graphics mode with just a shell and with ‘ssh’ access works fine, which is why Azure VMs didn’t see the issue.

The original change went into the mainline Linux kernel version 5.10, and the change is correct there. It provides a significant performance improvement for the Hyper-V frame buffer. So we wanted it backported to the older releases. Unfortunately, a straight backport breaks in kernel version 5.4 and earlier. The backport needs a minor modification to work correctly 4.15, but we didn’t spot that immediately, mostly because we rarely use graphic desktops.

The 4.15.0-137.141 kernel in the queue already, so this issue will be resolved and it only affects 136 - not 135 or 137.

[Marcelo Cerri (mhcerri)]

Hi, Luiz.

Can you test if the same problem happens with the version in bionic-proposed?