[pve-devel] [PATCH qemu-server] cfg2cmd: turn smm off when SeaBIOS and serial display are used

[Fabian Ebner]

Am 05.11.21 um 14:12 schrieb Thomas Lamprecht:
> On 05.11.21 14:06, Fabian Ebner wrote:
>> 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 at proxmox.com>
>> ---
>>   PVE/QemuServer.pm                    | 12 ++++++++++
>>   test/cfg2cmd/seabios_serial.conf     | 16 ++++++++++++++
>>   test/cfg2cmd/seabios_serial.conf.cmd | 33 ++++++++++++++++++++++++++++
>>   3 files changed, 61 insertions(+)
>>   create mode 100644 test/cfg2cmd/seabios_serial.conf
>>   create mode 100644 test/cfg2cmd/seabios_serial.conf.cmd
>>
>> diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
>> index 763c412..9b76512 100644
>> --- a/PVE/QemuServer.pm
>> +++ b/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);
> 
> doesn't that breaks live migration or do we know that it could never work with smm=on
> under seabios + display=serial, so that there can no running VM that could be live
> migrated?
> 

Stefan tested migration in both direction when the pve-qemu patch was 
dropped [0], but he did sound more confident about the smm=off -> smm=on 
direction. And now the scenario Wolfgang mentioned would actually be 
relevant, because we can get into a situation where smm=off -> smm=on -> 
smm=off by migrating from older -> old -> new. I'll test around some 
more and see if I can break it.

[0]: https://lists.proxmox.com/pipermail/pve-devel/2021-August/049778.html