Debian 10 VM on Proxmox, SDDM won't start when GPU passthru

[samtsui70]

I am running a Debian 10 VM on Proxmox server. A few days ago I backup all my VMs, wiped my Proxmox 5.4 server and installed Proxmox 6, then restored all my VMs. But now the Debian 10 VM cannot start SDDM if I tried to GPU passthrough my RX580 card.

The SDDM of this Debian VM launched normally when not trying to passthrough the RX580 card. But when trying to GPU passthrough, Debian booted into command mode only (it did show up on the monitor connected to the RX580 card so GPU passthrough was successful).

I checked the sddm.service status, below is the result:

Code: Select all

● sddm.service - Simple Desktop Display Manager
   Loaded: loaded (/lib/systemd/system/sddm.service; indirect; vendor preset: enabled)
   Active: failed (Result: signal) since Sun 2019-09-08 17:04:16 HKT; 3min 56s ago
     Docs: man:sddm(1)
           man:sddm.conf(5)
  Process: 866 ExecStartPre=/bin/sh -c [ "$(basename $(cat /etc/X11/default-display-manager 2>/dev/null))" = "sddm" ] (code=exited, status=0/SUCCESS)
  Process: 869 ExecStart=/usr/bin/sddm (code=killed, signal=ABRT)
 Main PID: 869 (code=killed, signal=ABRT)

Sep 08 17:04:16 sam-debian2 systemd[1]: sddm.service: Service RestartSec=1s expired, scheduling restart.
Sep 08 17:04:16 sam-debian2 systemd[1]: sddm.service: Scheduled restart job, restart counter is at 5.
Sep 08 17:04:16 sam-debian2 systemd[1]: Stopped Simple Desktop Display Manager.
Sep 08 17:04:16 sam-debian2 systemd[1]: sddm.service: Start request repeated too quickly.
Sep 08 17:04:16 sam-debian2 systemd[1]: sddm.service: Failed with result 'signal'.
Sep 08 17:04:16 sam-debian2 systemd[1]: Failed to start Simple Desktop Display Manager.

I also checked "journalctl", below is the result with error message:

Code: Select all

Sep 08 17:04:14 sam-debian2 sddm[869]: Display server starting...
Sep 08 17:04:14 sam-debian2 sddm[869]: Running: /usr/bin/X -nolisten tcp -auth /var/run/sddm/{28f81c44-e5bd-449a-86e8-c2ee3f5f3483} -background none -noreset -displayfd 17 -seat seat0 vt7
Sep 08 17:04:14 sam-debian2 sddm[869]: Failed to read display number from pipe
Sep 08 17:04:14 sam-debian2 sddm[869]: Display server failed to start. Exiting
Sep 08 17:04:14 sam-debian2 systemd[1]: sddm.service: Main process exited, code=killed, status=6/ABRT
Sep 08 17:04:14 sam-debian2 systemd[1]: sddm.service: Failed with result 'signal'.
Sep 08 17:04:16 sam-debian2 systemd[1]: sddm.service: Service RestartSec=1s expired, scheduling restart.
Sep 08 17:04:16 sam-debian2 systemd[1]: sddm.service: Scheduled restart job, restart counter is at 5.
Sep 08 17:04:16 sam-debian2 systemd[1]: Stopped Simple Desktop Display Manager.
Sep 08 17:04:16 sam-debian2 systemd[1]: sddm.service: Start request repeated too quickly.
Sep 08 17:04:16 sam-debian2 systemd[1]: sddm.service: Failed with result 'signal'.
Sep 08 17:04:16 sam-debian2 systemd[1]: Failed to start Simple Desktop Display Manager.

I tried to google with "failed to read display number from pipe"; "Failed with result 'signal'" etc, so far can't find anything useful. This Debian VM was completely working in Proxmox 5.4, SDDM started normally with GPU passthrough. I have no idea why restoring it in Proxmox 6 will have this problem. Can anyone please help? Many thanks!

Not sure if these information matters, but here they are:

• Proxmox version 6.0-4
  Debian GNU/Linux 10
  Kernel Version 4.19.0-6-amd64
  KDE Plasma Version 5.14.5
  SDDM Version 0.18.0-1

[ruwolf]

What do dmesg and /var/log/Xorg.0.log show for you?