[Qemu-devel] [PULL v2 14/15] pc: leave more space for BIOS allocations

["Michael S. Tsirkin" <mst@redhat.com>]

Since QEMU 2.1, we are allocating more space for ACPI tables, so no
space is left after initrd for the BIOS to allocate memory.

Besides ACPI tables, there are a few other uses of high memory in
SeaBIOS: SMBIOS tables and USB drivers use it in particular.  These uses
allocate a very small amount of memory.  Malloc metadata also lives
there.  So we need _some_ extra padding there to avoid initrd breakage,
but not much.

John Snow found a case where RHEL5 was broken by the recent change to
ACPI_TABLE_SIZE; in his case 4KB of extra padding are fine, but just to
be safe I am adding 32KB, which is roughly the same amount of padding
that was left by QEMU 2.0 and earlier.

Move initrd to leave some space for the BIOS.

Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reported-by: John Snow <jsnow@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/i386/pc.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index b6c9b61..9ac5bd2 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -72,8 +72,10 @@
 #define DPRINTF(fmt, ...)
 #endif
 
-/* Leave a chunk of memory at the top of RAM for the BIOS ACPI tables.  */
-unsigned acpi_data_size = 0x20000;
+/* Leave a chunk of memory at the top of RAM for the BIOS ACPI tables
+ * (128K) and other BIOS datastructures (less than 4K reported to be used at
+ * the moment, 32K should be enough for a while).  */
+unsigned acpi_data_size = 0x20000 + 0x8000;
 void pc_set_legacy_acpi_data_size(void)
 {
     acpi_data_size = 0x10000;
-- 
MST