cfg2cmd: turn smm off when SeaBIOS and serial display are used

Since commit 277d33454f77ec1d1e0bc04e37621e4dd2424b67 in pve-qemu,
smm=off is no longer the default, but with SeaBIOS and serial display,
this can lead to a boot loop.

Reported in the community forum [0] and reproduced with a Debian 10
VM.

[0]: https://forum.proxmox.com/threads/pve-7-0-all-vms-with-cloud-init-seabios-fail-during-boot-process-bootloop-disk-not-found.97310/post-427129

Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>

PVE/QemuServer.pm

@@ -3403,6 +3403,16 @@ my sub get_cpuunits {
     my ($conf) = @_;
     return $conf->{cpuunits} // (PVE::CGroup::cgroup_mode() == 2 ? 100 : 1024);
 }
+
+# Since commit 277d33454f77ec1d1e0bc04e37621e4dd2424b67 in pve-qemu, smm is not off by default
+# anymore. But smm=off seems to be required when using SeaBIOS and serial display.
+my sub should_disable_smm {
+    my ($conf, $vga) = @_;
+
+    return (!defined($conf->{bios}) || $conf->{bios} eq 'seabios') &&
+	$vga->{type} && $vga->{type} =~ m/^serial\d+$/;
+}
+
 sub config_to_command {
     my ($storecfg, $vmid, $conf, $defaults, $forcemachine, $forcecpu,
         $pbs_backing) = @_;
@@ -4002,6 +4012,8 @@ sub config_to_command {
 	push @$machineFlags, 'accel=tcg';
     }
 
+    push @$machineFlags, 'smm=off' if should_disable_smm($conf, $vga);
+
     my $machine_type_min = $machine_type;
     if ($add_pve_version) {
 	$machine_type_min =~ s/\+pve\d+$//;

test/cfg2cmd/seabios_serial.conf

@@ -0,0 +1,16 @@
+# TEST: Test for smm-related regression with SeaBIOS and serial display
+bootdisk: scsi0
+cores: 3
+ide2: none,media=cdrom
+memory: 768
+name: seabiosserial
+net0: virtio=A2:C0:43:77:08:A0,bridge=vmbr0
+numa: 0
+ostype: l26
+scsi0: local:8006/vm-8006-disk-0.qcow2,discard=on,size=104858K
+scsihw: virtio-scsi-pci
+serial0: socket
+smbios1: uuid=7b10d7af-b932-4c66-b2c3-3996152ec465
+sockets: 1
+vga: serial0
+vmgenid: c773c261-d800-4348-9f5d-167fadd53cf8

test/cfg2cmd/seabios_serial.conf.cmd

@@ -0,0 +1,33 @@
+/usr/bin/kvm \
+  -id 8006 \
+  -name seabiosserial \
+  -no-shutdown \
+  -chardev 'socket,id=qmp,path=/var/run/qemu-server/8006.qmp,server=on,wait=off' \
+  -mon 'chardev=qmp,mode=control' \
+  -chardev 'socket,id=qmp-event,path=/var/run/qmeventd.sock,reconnect=5' \
+  -mon 'chardev=qmp-event,mode=control' \
+  -pidfile /var/run/qemu-server/8006.pid \
+  -daemonize \
+  -smbios 'type=1,uuid=7b10d7af-b932-4c66-b2c3-3996152ec465' \
+  -smp '3,sockets=1,cores=3,maxcpus=3' \
+  -nodefaults \
+  -boot 'menu=on,strict=on,reboot-timeout=1000,splash=/usr/share/qemu-server/bootsplash.jpg' \
+  -nographic \
+  -cpu kvm64,enforce,+kvm_pv_eoi,+kvm_pv_unhalt,+lahf_lm,+sep \
+  -m 768 \
+  -device 'pci-bridge,id=pci.1,chassis_nr=1,bus=pci.0,addr=0x1e' \
+  -device 'pci-bridge,id=pci.2,chassis_nr=2,bus=pci.0,addr=0x1f' \
+  -device 'vmgenid,guid=c773c261-d800-4348-9f5d-167fadd53cf8' \
+  -device 'piix3-usb-uhci,id=uhci,bus=pci.0,addr=0x1.0x2' \
+  -chardev 'socket,id=serial0,path=/var/run/qemu-server/8006.serial0,server=on,wait=off' \
+  -device 'isa-serial,chardev=serial0' \
+  -device 'virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3' \
+  -iscsi 'initiator-name=iqn.1993-08.org.debian:01:aabbccddeeff' \
+  -drive 'if=none,id=drive-ide2,media=cdrom,aio=io_uring' \
+  -device 'ide-cd,bus=ide.1,unit=0,drive=drive-ide2,id=ide2,bootindex=200' \
+  -device 'virtio-scsi-pci,id=scsihw0,bus=pci.0,addr=0x5' \
+  -drive 'file=/var/lib/vz/images/8006/vm-8006-disk-0.qcow2,if=none,id=drive-scsi0,discard=on,format=qcow2,cache=none,aio=io_uring,detect-zeroes=unmap' \
+  -device 'scsi-hd,bus=scsihw0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0,bootindex=100' \
+  -netdev 'type=tap,id=net0,ifname=tap8006i0,script=/var/lib/qemu-server/pve-bridge,downscript=/var/lib/qemu-server/pve-bridgedown,vhost=on' \
+  -device 'virtio-net-pci,mac=A2:C0:43:77:08:A0,netdev=net0,bus=pci.0,addr=0x12,id=net0,bootindex=300' \
+  -machine 'smm=off,type=pc+pve0'