Include "-cpu" parameter with live-migration

This is required to support custom CPU models, since the
"cpu-models.conf" file is not versioned, and can be changed while a VM
using a custom model is running. Changing the file in such a state can
lead to a different "-cpu" argument on the receiving side.

This patch fixes this by passing the entire "-cpu" option (extracted
from /proc/.../cmdline) as a "qm start" parameter. Note that this is
only done if the VM to migrate is using a custom model (which we can
check just fine, since the <vmid>.conf *is* versioned with pending
changes), thus not breaking any live-migration directionality.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>

PVE/API2/Qemu.pm

@@ -2024,6 +2024,11 @@ __PACKAGE__->register_method({
 		optional => 1,
 	    },
 	    machine => get_standard_option('pve-qemu-machine'),
+	    'force-cpu' => {
+		description => "Override QEMU's -cpu argument with the given string.",
+		type => 'string',
+		optional => 1,
+	    },
 	    targetstorage => get_standard_option('pve-targetstorage'),
 	    timeout => {
 		description => "Wait maximal timeout seconds.",
@@ -2048,6 +2053,7 @@ __PACKAGE__->register_method({
 	my $timeout = extract_param($param, 'timeout');
 
 	my $machine = extract_param($param, 'machine');
+	my $force_cpu = extract_param($param, 'force-cpu');
 
 	my $get_root_param = sub {
 	    my $value = extract_param($param, $_[0]);
@@ -2132,6 +2138,7 @@ __PACKAGE__->register_method({
 		    skiplock => $skiplock,
 		    forcemachine => $machine,
 		    timeout => $timeout,
+		    forcecpu => $force_cpu,
 		};
 
 		PVE::QemuServer::vm_start($storecfg, $vmid, $params, $migrate_opts);

PVE/QemuMigrate.pm

@@ -17,6 +17,7 @@ use PVE::ReplicationState;
 use PVE::Storage;
 use PVE::Tools;
 
+use PVE::QemuServer::CPUConfig;
 use PVE::QemuServer::Drive;
 use PVE::QemuServer::Helpers qw(min_version);
 use PVE::QemuServer::Machine;
@@ -227,7 +228,17 @@ sub prepare {
 
 	$self->{forcemachine} = PVE::QemuServer::Machine::qemu_machine_pxe($vmid, $conf);
 
+	# To support custom CPU types, we keep QEMU's "-cpu" parameter intact.
+	# Since the parameter itself contains no reference to a custom model,
+	# this makes migration independent of changes to "cpu-models.conf".
+	if ($conf->{cpu}) {
+	    my $cpuconf = PVE::QemuServer::CPUConfig::parse_cpu_conf_basic($conf->{cpu});
+	    if ($cpuconf && PVE::QemuServer::CPUConfig::is_custom_model($cpuconf->{cputype})) {
+		$self->{forcecpu} = PVE::QemuServer::CPUConfig::get_cpu_from_running_vm($pid);
+	    }
+	}
     }
+
     my $loc_res = PVE::QemuServer::check_local_resources($conf, 1);
     if (scalar @$loc_res) {
 	if ($self->{running} || !$self->{opts}->{force}) {
@@ -662,6 +673,10 @@ sub phase2 {
 	push @$cmd, '--machine', $self->{forcemachine};
     }
 
+    if ($self->{forcecpu}) {
+	push @$cmd, '--force-cpu', $self->{forcecpu};
+    }
+
     if ($self->{online_local_volumes}) {
 	push @$cmd, '--targetstorage', ($self->{opts}->{targetstorage} // '1');
     }

PVE/QemuServer.pm

@@ -2933,7 +2933,7 @@ sub query_understood_cpu_flags {
 }
 
 sub config_to_command {
-    my ($storecfg, $vmid, $conf, $defaults, $forcemachine) = @_;
+    my ($storecfg, $vmid, $conf, $defaults, $forcemachine, $forcecpu) = @_;
 
     my $cmd = [];
     my $globalFlags = [];
@@ -3339,7 +3339,12 @@ sub config_to_command {
 	push @$rtcFlags, 'base=localtime';
     }
 
-    push @$cmd, get_cpu_options($conf, $arch, $kvm, $kvm_off, $machine_version, $winversion, $gpu_passthrough);
+    if ($forcecpu) {
+	push @$cmd, '-cpu', $forcecpu;
+    } else {
+	push @$cmd, get_cpu_options($conf, $arch, $kvm, $kvm_off,
+	    $machine_version, $winversion, $gpu_passthrough);
+    }
 
     PVE::QemuServer::Memory::config($conf, $vmid, $sockets, $cores, $defaults, $hotplug_features, $cmd);
 
@@ -4837,6 +4842,7 @@ sub vm_start {
 #   statefile => 'tcp', 'unix' for migration or path/volid for RAM state
 #   skiplock => 0/1, skip checking for config lock
 #   forcemachine => to force Qemu machine (rollback/migration)
+#   forcecpu => a QEMU '-cpu' argument string to override get_cpu_options
 #   timeout => in seconds
 #   paused => start VM in paused state (backup)
 #   resume => resume from hibernation
@@ -4884,7 +4890,8 @@ sub vm_start_nolock {
 	print "Resuming suspended VM\n";
     }
 
-    my ($cmd, $vollist, $spice_port) = config_to_command($storecfg, $vmid, $conf, $defaults, $forcemachine);
+    my ($cmd, $vollist, $spice_port) = config_to_command($storecfg, $vmid, $conf,
+	$defaults, $forcemachine, $params->{forcecpu});
 
     my $migration_ip;
     my $get_migration_ip = sub {

PVE/QemuServer/CPUConfig.pm

@@ -106,6 +106,8 @@ my @supported_cpu_flags = (
 my $cpu_flag_supported_re = qr/([+-])(@{[join('|', @supported_cpu_flags)]})/;
 my $cpu_flag_any_re = qr/([+-])([a-zA-Z0-9\-_\.]+)/;
 
+our $qemu_cmdline_cpu_re = qr/^((?>[+-]?[\w\-_=]+,?)+)$/;
+
 my $cpu_fmt = {
     cputype => {
 	description => "Emulated CPU type. Can be default or custom name (custom model names must be prefixed with 'custom-').",
@@ -413,6 +415,18 @@ sub add_hyperv_enlightenments {
     }
 }
 
+sub get_cpu_from_running_vm {
+    my ($pid) = @_;
+
+    my $cmdline = PVE::QemuServer::Helpers::parse_cmdline($pid);
+    die "could not read commandline of running machine\n"
+	if !$cmdline->{cpu}->{value};
+
+    # sanitize and untaint value
+    $cmdline->{cpu}->{value} =~ $qemu_cmdline_cpu_re;
+    return $1;
+}
+
 __PACKAGE__->register();
 __PACKAGE__->init();