multiboot: fix e801 memory map

The e801 memory sizes in the multiboot structures hard-code the available
low memory to 640.  However, the value should not include the size of the
EBDA.  Fill the value in the option ROM, getting the size of low memory
from the BIOS.

Cc: Alexander Graf <agraf@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

pc-bios/multiboot.bin

diff --git a/pc-bios/multiboot.bin b/pc-bios/multiboot.bin
index f74a6e1..7b3c174 100644
--- a/pc-bios/multiboot.bin
+++ b/pc-bios/multiboot.bin
Binary files differ

pc-bios/optionrom/multiboot.S

diff --git a/pc-bios/optionrom/multiboot.S b/pc-bios/optionrom/multiboot.S
index f08222a..003bcfb 100644
--- a/pc-bios/optionrom/multiboot.S
+++ b/pc-bios/optionrom/multiboot.S
@@ -75,6 +75,13 @@
 	shr		$4, %eax
 	mov		%ax, %fs
 
+	/* Account for the EBDA in the multiboot structure's e801
+	 * map.
+	 */
+	int		$0x12
+	cwtl
+	movl		%eax, %fs:4
+
 	/* ES = mmap_addr */
 	mov 		%fs:48, %eax
 	shr		$4, %eax