From: Rusty Russell <rusty@rustcorp.com.au>

BIOS ROM areas may not be mapped into the guest address space, so be careful
when touching those addresses to make sure they appear to be mapped.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 arch/i386/kernel/e820.c |    9 ++++++++-
 arch/i386/pci/pcbios.c  |    7 ++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff -puN arch/i386/kernel/setup.c~prep-for-paravirt-be-careful-about-touching-bios arch/i386/kernel/setup.c
diff -puN arch/i386/pci/pcbios.c~prep-for-paravirt-be-careful-about-touching-bios arch/i386/pci/pcbios.c
--- a/arch/i386/pci/pcbios.c~prep-for-paravirt-be-careful-about-touching-bios
+++ a/arch/i386/pci/pcbios.c
@@ -5,6 +5,7 @@
 #include <linux/pci.h>
 #include <linux/init.h>
 #include <linux/module.h>
+#include <asm/uaccess.h>
 #include "pci.h"
 #include "pci-functions.h"
 
@@ -301,7 +302,7 @@ static struct pci_raw_ops pci_bios_acces
 
 static struct pci_raw_ops * __devinit pci_find_bios(void)
 {
-	union bios32 *check;
+	union bios32 *check, sig;
 	unsigned char sum;
 	int i, length;
 
@@ -314,6 +315,10 @@ static struct pci_raw_ops * __devinit pc
 	for (check = (union bios32 *) __va(0xe0000);
 	     check <= (union bios32 *) __va(0xffff0);
 	     ++check) {
+		long sig;
+		if (__get_user(sig, &check->fields.signature))
+			continue;
+
 		if (check->fields.signature != BIOS32_SIGNATURE)
 			continue;
 		length = check->fields.length * 16;
diff -puN arch/i386/kernel/e820.c~prep-for-paravirt-be-careful-about-touching-bios arch/i386/kernel/e820.c
--- a/arch/i386/kernel/e820.c~prep-for-paravirt-be-careful-about-touching-bios
+++ a/arch/i386/kernel/e820.c
@@ -155,7 +155,14 @@ static struct resource standard_io_resou
 	.flags	= IORESOURCE_BUSY | IORESOURCE_IO
 } };
 
-#define romsignature(x) (*(unsigned short *)(x) == 0xaa55)
+static int romsignature(const unsigned char *x)
+{
+	unsigned short sig;
+	int ret = 0;
+	if (__get_user(sig, (const unsigned short *)x) == 0)
+		ret = (sig == 0xaa55);
+	return ret;
+}
 
 static int __init romchecksum(unsigned char *rom, unsigned long length)
 {
_