1 files changed, 55 insertions, 0 deletions

diff --git a/arch/x86/kernel/head.c b/arch/x86/kernel/head.c
new file mode 100644
index 000000000000..3e66bd364a9d
--- /dev/null
+++ b/arch/x86/kernel/head.c
@@ -0,0 +1,55 @@
+#include <linux/kernel.h>
+#include <linux/init.h>
+
+#include <asm/setup.h>
+#include <asm/bios_ebda.h>
+
+#define BIOS_LOWMEM_KILOBYTES 0x413
+
+/*
+ * The BIOS places the EBDA/XBDA at the top of conventional
+ * memory, and usually decreases the reported amount of
+ * conventional memory (int 0x12) too. This also contains a
+ * workaround for Dell systems that neglect to reserve EBDA.
+ * The same workaround also avoids a problem with the AMD768MPX
+ * chipset: reserve a page before VGA to prevent PCI prefetch
+ * into it (errata #56). Usually the page is reserved anyways,
+ * unless you have no PS/2 mouse plugged in.
+ */
+void __init reserve_ebda_region(void)
+{
+        unsigned int lowmem, ebda_addr;
+
+        /* To determine the position of the EBDA and the */
+        /* end of conventional memory, we need to look at */
+        /* the BIOS data area. In a paravirtual environment */
+        /* that area is absent. We'll just have to assume */
+        /* that the paravirt case can handle memory setup */
+        /* correctly, without our help. */
+        if (paravirt_enabled())
+                return;
+
+        /* end of low (conventional) memory */
+        lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES);
+        lowmem <<= 10;
+
+        /* start of EBDA area */
+        ebda_addr = get_bios_ebda();
+
+        /* Fixup: bios puts an EBDA in the top 64K segment */
+        /* of conventional memory, but does not adjust lowmem. */
+        if ((lowmem - ebda_addr) <= 0x10000)
+                lowmem = ebda_addr;
+
+        /* Fixup: bios does not report an EBDA at all. */
+        /* Some old Dells seem to need 4k anyhow (bugzilla 2990) */
+        if ((ebda_addr == 0) && (lowmem >= 0x9f000))
+                lowmem = 0x9f000;
+
+        /* Paranoia: should never happen, but... */
+        if ((lowmem == 0) || (lowmem >= 0x100000))
+                lowmem = 0x9f000;
+
+        /* reserve all memory between lowmem and the 1MB mark */
+        reserve_early_overlap_ok(lowmem, 0x100000, "BIOS reserved");
+}