Signed-off-by: Igor Mammedov <imamm...@redhat.com>
hw/i386/pc.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index f1c1013..f807932 100644
@@ -746,17 +746,15 @@ static FWCfgState *bochs_bios_init(AddressSpace *as,
/* FW_CFG_MAX_CPUS is a bit confusing/problematic on x86:
- * SeaBIOS needs FW_CFG_MAX_CPUS for CPU hotplug, but the CPU hotplug
- * QEMU<->SeaBIOS interface is not based on the "CPU index", but on the
- * ID of hotplugged CPUs. This means that FW_CFG_MAX_CPUS is not the
- * "maximum number of CPUs", but the "limit to the APIC ID values SeaBIOS
- * may see".
+ * For machine types prior to 1.8, SeaBIOS needs FW_CFG_MAX_CPUS for
+ * building MPTable, ACPI MADT, ACPI CPU hotplug and ACPI SRAT table,
+ * that tables are based on xAPIC ID and QEMU<->SeaBIOS interface
+ * for CPU hotplug also uses APIC ID and not "CPU index".
+ * This means that FW_CFG_MAX_CPUS is not the "maximum number of CPUs",
+ * but the "limit to the APIC ID values SeaBIOS may see".
- * So, this means we must not use max_cpus, here, but the maximum possible
- * APIC ID value, plus one.
- *  The only kind of "CPU identifier" used between SeaBIOS and QEMU is
- * the APIC ID, not the "CPU index"
+ * So for compatibility reasons with old BIOSes we are stuck with
+ * "etc/max-cpus" actually being apic_id_limit
fw_cfg_add_i16(fw_cfg, FW_CFG_MAX_CPUS, (uint16_t)pcms->apic_id_limit);
fw_cfg_add_i64(fw_cfg, FW_CFG_RAM_SIZE, (uint64_t)ram_size);