Claudia:
Claudia:
Claudia:
The last message on the console is always "[OK] Started Monitoring of LVM2 mirrors, snapshots, etc. using dmeventd or progress polling" at which point it just hangs. The cursor doesn't blink, and pressing enter doesn't do anything. Some keys cause it to beep, though, and it does respond to ctrl-alt-delete by rebooting after a few seconds, but the screen remains completely frozen during that time. So it feels like it's running normally except the screen is frozen. 4.0.1 installer worked fine on the same machine.

Any ideas on how to debug something like this?

Okay, so oddly enough I was able to get past this by pressing ctrl-alt-f1 repeatedly during dom0 init (systemd), **before** it freezes. At that point I could see the anaconda shell, followed by the graphical installer.

The installation went fine, but now I'm experiencing the same problem when booting the installed OS. It hangs at "Starting Show Plymouth Boot Screen... Starting dracut initqueue hook...", just before it should prompt for the disk password. I was able to get to the console-based (not graphical) disk password prompt a few times by pressing random keys, but I can't make it work reliably (or I don't know what I did exactly). Once again, it responds to ctrl-alt-delete but the screen is frozen.

In both cases (installer and installed), it seems to freeze within a few lines of "Starting Show Plymouth Boot Screen". So I have a feeling it's being caused when Plymouth tries to switch into graphical mode.

Any ideas would be helpful. Is there any way to make it boot in text mode up until lightdm?

Note, I'm using AMD Vega graphics, there is no dGPU, and neither of these problems were present on 4.0.1, even under kernel 4.19.

Okay, so I was able to disable plymouth by removing "rhgb quiet" from the kernel command line. Now, the last thing on the console before it freezes is "fb: switching to amdgpudrmfb from EFI VGA".

I looked it up, and this message has something to do with amdgpu. Adding "nomodeset" to the kernel command line fixed it. It gives me the text-based disk passphrase prompt, and eventually lightdm starts. It seems to run fine after that, but I don't know if running with nomodeset is really a good solution or not.

I still consider it a bug, because 1) amdgpu should work properly and not have to be disabled, and it worked in previous releases, and 2) AMD users should not have to debug the boot process and modify kernel parameters right out of the box.

Thoughts?

Apparently this is a known issue on my machine and many others. Many people have found that iommu=soft corrects the problem without disabling graphics drivers (amdgpu). I don't know if the Linux iommu parameter is effective when running under Xen. For me, changing nomodeset to iommu=soft just caused Qubes to boot loop, whereas before the screen would freeze.

I noticed that Qubes uses the Xen option iommu=no-igfx, which "controls whether the IOMMU in front of an Intel Graphics Device is enabled or not" and is "specific to Intel VT-d hardware". Could this have anything to do with it? It seems there is no AMD equivalent, and no way to specify arbitrary devices as exceptions to IOMMU. So any changes would affect all devices.

https://www.qubes-os.org/doc/intel-igfx-troubleshooting/

https://xenbits.xen.org/docs/unstable/misc/xen-command-line.html#iommu

I still don't understand why it worked fine out of the box in R4.0.1 though. Same for R4.1 pre-release (the installer, at least).

Anyone know anything about this?

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