[Qemu-devel] [PATCH v2 2/3] 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 bugs due to large tables.

Use it for 2.2+ 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-2.1.

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]

Thanks to the new linuxboot option ROM, the initrd is loaded 64k above.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/i386/pc_piix.c | 19 ++++++++++++++++---
 hw/i386/pc_q35.c  |  6 ++++--
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 060f6ec..0d3a191 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;
 /* Make sure that guest addresses aligned at 1Gbyte boundaries get mapped to
@@ -306,6 +306,12 @@ static void pc_init_pci(MachineState *machine)
     pc_init1(machine, 1, 1);
 }
 
+static void pc_compat_2_1(MachineState *machine)
+{
+    fixed_table_align = 0;
+    acpi_table_align = 131072;
+}
+
 static void pc_compat_2_0(MachineState *machine)
 {
     /* This value depends on the actual DSDT and SSDT compiled into
@@ -324,6 +330,7 @@ static void pc_compat_2_0(MachineState *machine)
      * 6652 is valid for QEMU 2.0, the right value for pc-i440fx-1.7 on
      * QEMU 1.7 it is 6414.  For RHEL/CentOS 7.0 it is 6418.
      */
+    pc_compat_2_1(machine);
     legacy_acpi_table_size = 6652;
     acpi_table_align = 4096;
     smbios_legacy_mode = true;
@@ -373,6 +380,12 @@ static void pc_compat_1_2(MachineState *machine)
     x86_cpu_compat_disable_kvm_features(FEAT_KVM, KVM_FEATURE_PV_EOI);
 }
 
+static void pc_init_pci_2_1(MachineState *machine)
+{
+    pc_compat_2_1(machine);
+    pc_init_pci(machine);
+}
+
 static void pc_init_pci_2_0(MachineState *machine)
 {
     pc_compat_2_0(machine);
@@ -476,7 +489,7 @@ static QEMUMachine pc_i440fx_machine_v2_2 = {
 static QEMUMachine pc_i440fx_machine_v2_1 = {
     PC_I440FX_2_1_MACHINE_OPTIONS,
     .name = "pc-i440fx-2.1",
-    .init = pc_init_pci,
+    .init = pc_init_pci_2_1,
     .compat_props = (GlobalProperty[]) {
         PC_COMPAT_2_1,
         { /* end of list */ }
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index d4a907c..3443f32 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -153,10 +153,12 @@ 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);
-- 
2.1.0