[Qemu-devel] [PATCH v4 09/10] pc: acpi: clarify why possible LAPIC entries must be present in MADT

[Igor Mammedov <imammedo@redhat.com>]

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
---
 hw/i386/acpi-build.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 48240e0..155198b 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -360,6 +360,12 @@ build_madt(GArray *table_data, GArray *linker, PCMachineState *pcms)
         if (apic_ids->cpus[i].cpu != NULL) {
             apic->flags = cpu_to_le32(1);
         } else {
+            /* ACPI spec says that LAPIC entry for non present
+             * CPU may be omitted from MADT or it must be marked
+             * as disabled. However omitting non present CPU from
+             * MADT breaks hotplug on linux. So possible CPUs
+             * should be put in MADT but kept disabled.
+             */
             apic->flags = cpu_to_le32(0);
         }
     }
-- 
1.8.3.1