[Qemu-devel] [PATCH v2 1/3] pc: introduce new ACPI table sizing algorithm

[Paolo Bonzini <pbonzini@redhat.com>]

Add padding after the DSDT.  Tables that vary depending on the
command-line arguments will have to be byte-equivalent across QEMU
versions >= 2.2, while fixed tables (including the DSDT) can be
changed freely.

This new algorithm will let us present smaller ACPI blobs to
the guest, which avoids bugs with -kernel/-initrd and 32-bit
RHEL5 guests.  However, this patch does not change the size of
the blobs yet; for now, the values of the parameters are tuned
to have 2.1-compatible sizes.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/i386/acpi-build.c | 11 +++++++----
 hw/i386/pc_piix.c    |  5 +++++
 include/hw/i386/pc.h |  2 ++
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index a313321..6bffc75 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -65,8 +65,6 @@
 #define ACPI_BUILD_LEGACY_CPU_AML_SIZE    97
 #define ACPI_BUILD_ALIGN_SIZE             0x1000
 
-#define ACPI_BUILD_TABLE_SIZE             0x20000
-
 typedef struct AcpiCpuInfo {
     DECLARE_BITMAP(found_cpus, ACPI_CPU_HOTPLUG_ID_LIMIT);
 } AcpiCpuInfo;
@@ -1597,6 +1595,10 @@ void acpi_build(PcGuestInfo *guest_info, AcpiBuildTables *tables)
     acpi_add_table(table_offsets, tables->table_data);
     build_fadt(tables->table_data, tables->linker, &pm, facs, dsdt);
 
+    if (guest_info->fixed_table_align) {
+        acpi_align_size(tables->table_data, guest_info->fixed_table_align);
+    }
+
     ssdt = tables->table_data->len;
     acpi_add_table(table_offsets, tables->table_data);
     build_ssdt(tables->table_data, tables->linker, &cpu, &pm, &misc, &pci,
@@ -1681,14 +1683,15 @@ void acpi_build(PcGuestInfo *guest_info, AcpiBuildTables *tables)
         g_array_set_size(tables->table_data, legacy_table_size);
     } else {
         /* Make sure we have a buffer in case we need to resize the tables. */
-        if (tables->table_data->len > ACPI_BUILD_TABLE_SIZE / 2) {
+        if (!guest_info->fixed_table_align &&
+	    tables->table_data->len > guest_info->acpi_table_align / 2) {
             /* As of QEMU 2.1, this fires with 160 VCPUs and 255 memory slots.  */
             error_report("Warning: ACPI tables are larger than 64k.");
             error_report("Warning: migration may not work.");
             error_report("Warning: please remove CPUs, NUMA nodes, "
                          "memory slots or PCI bridges.");
         }
-        acpi_align_size(tables->table_data, ACPI_BUILD_TABLE_SIZE);
+        acpi_align_size(tables->table_data, guest_info->acpi_table_align);
     }
 
     acpi_align_size(tables->linker, ACPI_BUILD_ALIGN_SIZE);
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 103d756..060f6ec 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -61,6 +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 bool smbios_defaults = true;
 static bool smbios_legacy_mode;
 /* Make sure that guest addresses aligned at 1Gbyte boundaries get mapped to
@@ -164,6 +166,8 @@ static void pc_init1(MachineState *machine,
 
     guest_info->has_acpi_build = has_acpi_build;
     guest_info->legacy_acpi_table_size = legacy_acpi_table_size;
+    guest_info->fixed_table_align = fixed_table_align;
+    guest_info->acpi_table_align = acpi_table_align;
 
     guest_info->isapc_ram_fw = !pci_enabled;
     guest_info->has_reserved_memory = has_reserved_memory;
@@ -321,6 +325,7 @@ static void pc_compat_2_0(MachineState *machine)
      * QEMU 1.7 it is 6414.  For RHEL/CentOS 7.0 it is 6418.
      */
     legacy_acpi_table_size = 6652;
+    acpi_table_align = 4096;
     smbios_legacy_mode = true;
     has_reserved_memory = false;
     pc_set_legacy_acpi_data_size();
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index 77316d5..517e729 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -94,6 +94,8 @@ struct PcGuestInfo {
     uint64_t *node_cpu;
     FWCfgState *fw_cfg;
     int legacy_acpi_table_size;
+    int fixed_table_align;
+    int acpi_table_align;
     bool has_acpi_build;
     bool has_reserved_memory;
 };
-- 
2.1.0