LXR linux/arch/x86/kernel/head.c

   1#include <linux/kernel.h>
   2#include <linux/init.h>
   3
   4#include <asm/setup.h>
   5#include <asm/bios_ebda.h>
   6
   7#define BIOS_LOWMEM_KILOBYTES 0x413
   8
   9/*
  10 * The BIOS places the EBDA/XBDA at the top of conventional
  11 * memory, and usually decreases the reported amount of
  12 * conventional memory (int 0x12) too. This also contains a
  13 * workaround for Dell systems that neglect to reserve EBDA.
  14 * The same workaround also avoids a problem with the AMD768MPX
  15 * chipset: reserve a page before VGA to prevent PCI prefetch
  16 * into it (errata #56). Usually the page is reserved anyways,
  17 * unless you have no PS/2 mouse plugged in.
  18 */
  19void __init reserve_ebda_region(void)
  20{
  21        unsigned int lowmem, ebda_addr;
  22
  23        /* To determine the position of the EBDA and the */
  24        /* end of conventional memory, we need to look at */
  25        /* the BIOS data area. In a paravirtual environment */
  26        /* that area is absent. We'll just have to assume */
  27        /* that the paravirt case can handle memory setup */
  28        /* correctly, without our help. */
  29        if (paravirt_enabled())
  30                return;
  31
  32        /* end of low (conventional) memory */
  33        lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES);
  34        lowmem <<= 10;
  35
  36        /* start of EBDA area */
  37        ebda_addr = get_bios_ebda();
  38        printk(KERN_INFO "BIOS EBDA/lowmem at: %08x/%08x\n", ebda_addr, lowmem);
  39
  40        /* Fixup: bios puts an EBDA in the top 64K segment */
  41        /* of conventional memory, but does not adjust lowmem. */
  42        if ((lowmem - ebda_addr) <= 0x10000)
  43                lowmem = ebda_addr;
  44
  45        /* Fixup: bios does not report an EBDA at all. */
  46        /* Some old Dells seem to need 4k anyhow (bugzilla 2990) */
  47        if ((ebda_addr == 0) && (lowmem >= 0x9f000))
  48                lowmem = 0x9f000;
  49
  50        /* Paranoia: should never happen, but... */
  51        if ((lowmem == 0) || (lowmem >= 0x100000))
  52                lowmem = 0x9f000;
  53
  54        /* reserve all memory between lowmem and the 1MB mark */
  55        reserve_early_overlap_ok(lowmem, 0x100000, "BIOS reserved");
  56}
  57