Redhat 7.9 VM not working after latest update

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Hello, I have a Redhat 7.9 VM on Windows 10 Hyper-V. It was fine, but after I applied the latest update, on boot the VM doesn't start. It shows a black screen with a some odd red symbol on the top, and it doesn't start. I attach the log file of the installation.

Any help would be appreciated.

Thanks, Marco



Also reported for CentOS. The kernel in question is 3.10.0-1160.21.1.el7.x86_64.

Bug report filed:

After updating to kernel version 3.10.0-1160.21.1.el7.x86_64 on a Hyper-V (Windows 10) VM, the OS will not boot. There appear to be error messages output but the display is affected (squashed) and they are illegible. Selecting another kernel from the grub menu allows the OS to boot.

  • The following patch seems to have caused the issue:

[Hyper-V][RHEL-7.9]video: hyperv_fb: Fix the cache type when mapping the VRAM Edit (BZ#1908896)

kernel commit: commit 5f1251a48c17b54939d7477305e39679a565382c Author: Dexuan Cui Date: Tue Nov 17 16:03:05 2020 -0800

video: hyperv_fb: Fix the cache type when mapping the VRAM

  • The issue has been fixed by:

Stable kernel commit: commit 452f087d2ff6decf298149e0bfd9fa5c212a636d Author: Dexuan Cui Date: Sat Jan 9 14:53:58 2021 -0800

video: hyperv_fb: Fix the mmap() regression for v5.4.y and older

Thanks for that. I've set some bug flags and added some public and private comments to hopefully help it be addressed quickly in 7.9.z

I've built a CentOSPlus kernel (kernel-plus) with the patch that is supposed to fix the problem. It is available from:

Anyone affected by this problem is encouraged to give it a try. Feedback welcome.

Hi Akemi and Jamie,

Is this pure Windows 10 related, or a generic Hyper-V issue?

I mean are Azure users also effected?


Jan Gerrit Kootstra

The problem is related to hyper-v, so I don't think azure is affected.

Thanks, I'll wait for the solution in the next Redhat 7.9 update. I logged in but I'm not allowed to see the topic. Red Hat Bugzilla – Bug Access Denied You are not authorized to access bug #1941841. Most likely the bug has been restricted for internal development processes and we cannot grant access.

I am a bit unhappy as I cannot follow the status of the solution. Anyway I hope that updates will be made available on this thread, or on the similar one for CentOS.

All kernel-related bug reports automatically become inaccessible to the public. However if the issue has no security concern, it might be made public. So, let's ask Jamie. :)

I forgot to mention that the plus kernel was provided strictly for testing purposes. Any report with positive results may help accelerate the bug fix process, is my hope.

I'm not sure why the bug was marked Private. There is no history of anyone intentionally making it private, perhaps the template does that at creation.

Anyway, I've removed the restriction so the bug is public.

Thank you, Jamie.

Once upon a time, RH set up the bugzilla in such a way that all bugs submitted under the category "kernel" become inaccessible (group redhat) by default.

I have just checked, I have access to the topic. Thank you very much, Jamie and Akemi

Hi Marco,

Could you provide an answer for the question regarding the host build version?

On my PC Dell Precison 5820, Windows 10 for Workstation, version 20H2, OS build 19042.870, this is the Hyper-V version:

[marco@redhat7 ~]$ dmesg | grep "Hyper-V Host Build" [ 0.000000] Hyper-V Host Build:19041-10.0-0-0.870


Thank you, Marco. I've copied your result to the RHBZ. Now that it is open to the public, you could post your note there, if you have a bugzilla account. :)