[Qemu-devel] [PATCH v2 7/4] pc: go back to smaller ACPI tables

[Paolo Bonzini <pbonzini@redhat.com>]

The new algorithm introduced by the previous patch lets us make tables
smaller and avoid migration bugs due to large tables.

Use it for 2.3+ machine types by tweaking the default fixed_table_align
and acpi_table_align values.  At the same time, preserve backwards-compatible
logic for pc-i440fx-2.2.

Without this patch:
[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000007fdffff] usable
[    0.000000] BIOS-e820: [mem 0x0000000007fe0000-0x0000000007ffffff] reserved
...
[    0.000000] init_memory_mapping: [mem 0x07000000-0x07fdffff] usable
[    0.000000] RAMDISK: [mem 0x07112000-0x07fdffff]

With this patch:
[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000007ffafff] usable
[    0.000000] BIOS-e820: [mem 0x0000000007ffb000-0x0000000007ffffff] reserved
...
[    0.000000] init_memory_mapping: [mem 0x07000000-0x07ffafff]
[    0.000000] RAMDISK: [mem 0x07122000-0x07feffff]

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/i386/pc_piix.c | 6 ++++--
 hw/i386/pc_q35.c  | 6 ++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 16de5c9..a5e36b9 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -61,8 +61,8 @@ static const int ide_irq[MAX_IDE_BUS] = { 14, 15 };
 
 static bool has_acpi_build = true;
 static int legacy_acpi_table_size;
-static int fixed_table_align = 0;
-static int acpi_table_align = 131072;
+static int fixed_table_align = 16384;
+static int acpi_table_align = 4096;
 static bool smbios_defaults = true;
 static bool smbios_legacy_mode;
 static bool smbios_uuid_encoded = true;
@@ -332,6 +332,8 @@ static void pc_compat_2_2(MachineState *machine)
     x86_cpu_compat_set_features("Haswell", FEAT_1_ECX, 0, CPUID_EXT_RDRAND);
     x86_cpu_compat_set_features("Broadwell", FEAT_1_ECX, 0, CPUID_EXT_F16C);
     x86_cpu_compat_set_features("Broadwell", FEAT_1_ECX, 0, CPUID_EXT_RDRAND);
+    fixed_table_align = 0;
+    acpi_table_align = 131072;
 }
 
 static void pc_compat_2_1(MachineState *machine)
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index 7ba0535..4fd9527 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -155,10 +155,12 @@ static void pc_q35_init(MachineState *machine)
     guest_info->has_acpi_build = has_acpi_build;
     guest_info->has_reserved_memory = has_reserved_memory;
 
-    /* Migration was not supported in 2.0 for Q35, so do not bother
-     * with this hack (see hw/i386/acpi-build.c).
+    /* Migration was not supported in 2.0 for Q35, so do not bother with
+     * hacks around the ACPI table size (see hw/i386/acpi-build.c).
      */
     guest_info->legacy_acpi_table_size = 0;
+    guest_info->fixed_table_align = 16384;
+    guest_info->acpi_table_align = 4096;
 
     if (smbios_defaults) {
         MachineClass *mc = MACHINE_GET_CLASS(machine);
-- 
1.8.3.1