Hi Ray,

I attached the output of 'udevadm info --export-db' on both 'gdm-40.0-12.el8.x86_64' and 'gdm-40.0-13.el8.x86_64'.

1.Checked with gdm-40.0-13.el8.x86_64， GUI can display and login, but the item changed in the gear on login page (screenshot attached): "Standard（X11 as display server) on Xorg" --> "Standard（X11 as display server)", is this change expected?

2.Checked with the script of comment 8, the cli result as below:

a>
\n\n\nChecking if Xorg fallback worked-: OK
test-fallback.sh: line 62: 11029 Terminated              journalctl -f -n0
wayland x11
[root@vm-198-172 ~]# rpm -q gdm
gdm-40.0-13.el8.x86_64

GUI will create a new user:  test-fallback-session-user， but gui user list will disappear a while after clicking the 'test-fallback-session-user', then GUI will display the user selection page again, is this the script expected result?

b>
\n\n\nChecking if Xorg fallback worked-: FAILED
md5sum: WARNING: 1 computed checksum did NOT match
test-fallback.sh: line 62: 78354 Terminated              journalctl -f -n0
wayland wayland
[root@bootp-73-199-210 ~]# rpm -q gdm
gdm-40.0-12.el8.x86_64

The bug issue appeared, GUI disappeared, even it was configured: WaylandEnable=false in the [daemon] section of /etc/gdm/custom.conf

3. About comment 10: 
"I'd like to add a udev rule to force hyperv to go straight to xorg rather than relying on fallback.  It should speed up boot and side step this class of bugs for the future."

It only needs on RHEL8, but not RHEL9, since on RHEL9, it supported wayland (https://bugzilla.redhat.com/show_bug.cgi?id=1972122), right?

If so, will the rule still take effect when upgrading from RHEL8 to RHEL9?

Thanks

1. is a change in gnome-session from bug 1962211 . it's not directly related to this gdm build. i guess you probably upgraded gnome-session at the same time when installing the new package.
2. yes that's expected. when the script is running it does auto login to an dummy session that's just a black screen.  When the script is finished it returns to the login screen.

The important part of the script is "Checking if Xorg fallback worked-: OK" .  Of course the script was just to illustrate how it could potentially be tested in GDMs CI tests. The important thing is that HyperV works...

3. That's right, the udev rule ships with GDM so it will go away in RHEL 9 when GDM is upgraded.

okay i've got a scratch build going that should disable wayland on HyperV too: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=39499317

Checked on compose: RHEL-8.5.0-20210906.n.0-x86_64 (kernel: 4.18.0-339.el8.x86_64, gdm: gdm-40.0-13.el8.x86_64)

1. Now the GUI installation works well with GEN1 and GEN2

2. Also checked login with each display server, GUI login and display well
-Standard(X11 display server)
-Classic(X11 display server)
-Custom
-User script

3.Run the script of comment 8:
GEN1:
\n\n\nChecking if Xorg fallback worked-: OK
test-fallback.sh: line 62: 15623 Terminated              journalctl -f -n0
wayland x11

GEN2:
\n\n\nChecking if Xorg fallback worked-: OK
test-fallback.sh: line 62: 14197 Terminated              journalctl -f -n0
wayland x11

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (Moderate: GNOME security, bug fix, and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2021:4381