Change 5c371b31be3203 in stable breaks Xen

[Jeremy Fitzhardinge <jeremy@goop.org>]

I have a report of Xen breaking between 2.6.27.5 and .6.  I bisected it 
down to change:

commit 5c371b31be32033b0a4a993431484da8a2305369
Author: Yinghai Lu <yhlu.kernel@gmail.com>
Date:   Mon Sep 22 02:52:26 2008 -0700

    x86: fix CONFIG_X86_RESERVE_LOW_64K=y
   
    commit 2216d199b1430d1c0affb1498a9ebdbd9c0de439 upstream
   
    The bad_bios_dmi_table() quirk never triggered because we do DMI setup
    too late. Move it a bit earlier.
   
    Also change the CONFIG_X86_RESERVE_LOW_64K quirk to operate on the e820
    table directly instead of messing with early reservations - this handles
    overlaps (which do occur in this low range of RAM) more gracefully.
   
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

I haven't completely root-caused why this is OK in mainline but failing 
in stable, but this patch works around the problem.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
index 455575b..abed1dd 100644
--- a/drivers/firmware/dmi_scan.c
+++ b/drivers/firmware/dmi_scan.c
@@ -7,6 +7,7 @@
 #include <linux/bootmem.h>
 #include <linux/slab.h>
 #include <asm/dmi.h>
+#include <asm/xen/hypervisor.h>
 
 /*
  * DMI stands for "Desktop Management Interface".  It is part
@@ -364,6 +365,11 @@ void __init dmi_scan_machine(void)
        char __iomem *p, *q;
        int rc;
 
+#ifdef CONFIG_XEN
+       if (is_running_on_xen())
+               return;
+#endif
+
        if (efi_enabled) {
                if (efi.smbios == EFI_INVALID_TABLE_ADDR)
                        goto out;