[Qemu-devel] [PATCH] acpi: Use apic_id_limit when calculating legacy ACPI table size

[Eduardo Habkost <ehabkost@redhat.com>]

The code that calculates the legacy ACPI table size for migration
compatibility uses max_cpus when calculating legacy_aml_len (the size of
the DSDT and SSDT tables). However, the SSDT grows according to APIC ID
limit, not max_cpus.

The bug is not triggered very often because of the 4k alignment on the
table size. But it can be triggered if you are unlucky enough to cross a
4k boundary. For example, using the following:

  $ qemu-system-x86_64 -machine pc-i440fx-2.0 -smp 99,sockets=3,cores=33,threads=1
  qemu-system-x86_64: Warning: migration may not work.

Change the legacy_aml_len calculation to use apic_id_limit, to calculate
the right size.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 hw/i386/acpi-build.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index a4d0c0c..359fb43 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -1675,7 +1675,7 @@ void acpi_build(PcGuestInfo *guest_info, AcpiBuildTables *tables)
          */
         int legacy_aml_len =
             guest_info->legacy_acpi_table_size +
-            ACPI_BUILD_LEGACY_CPU_AML_SIZE * max_cpus;
+            ACPI_BUILD_LEGACY_CPU_AML_SIZE * guest_info->apic_id_limit;
         int legacy_table_size =
             ROUND_UP(tables->table_data->len - aml_len + legacy_aml_len,
                      ACPI_BUILD_ALIGN_SIZE);
-- 
1.9.3