+my $_host_bits;
+my sub get_host_phys_address_bits {
+ return $_host_bits if defined($_host_bits);
+
+ my $fh = IO::File->new ('/proc/cpuinfo', "r") or return;
+ while (defined(my $line = <$fh>)) {
+ # hopefully we never need to care about mixed (big.LITTLE) archs
+ if ($line =~ m/^address sizes\s*:\s*(\d+)\s*bits physical/i) {
+ $_host_bits = int($1);
+ $fh->close();
+ return $_host_bits;
+ }
+ }
+ $fh->close();
+ return; # undef, cannot really do anything..
+}
+
+my sub get_max_mem {
+ my ($conf) = @_;
+
+ my $cpu = {};
+ if (my $cpu_prop_str = $conf->{cpu}) {
+ $cpu = PVE::JSONSchema::parse_property_string('pve-vm-cpu-conf', $cpu_prop_str)
+ or die "Cannot parse cpu description: $cpu_prop_str\n";
+ }
+ my $bits;
+ if (my $phys_bits = $cpu->{'phys-bits'}) {
+ if ($phys_bits eq 'host') {
+ $bits = get_host_phys_address_bits();
+ } elsif ($phys_bits =~ /^(\d+)$/) {
+ $bits = int($phys_bits);
+ }
+ }
+
+ if (!defined($bits)) {
+ my $host_bits = get_host_phys_address_bits() // 36; # fixme: what fallback?
+ if ($cpu->{cputype} && $cpu->{cputype} =~ /^(host|max)$/) {
+ $bits = $host_bits;
+ } else {
+ $bits = $host_bits > 40 ? 40 : $host_bits; # take the smaller one
+ }
+ }
+
+ # remove 20 bits to get MB and half that as QEMU needs some overhead
+ my $bits_to_max_mem = int(1 << ($bits - 21));
+
+ return $bits_to_max_mem > 4*1024*1024 ? 4*1024*1024 : $bits_to_max_mem;
+}
+