[028/136] xen: check EFER for NX before setting up GDT mapping

[Greg KH]

2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

commit b75fe4e5b869f8dbebd36df64a7fcda0c5b318ed upstream.

x86-64 assumes NX is available by default, so we need to
explicitly check for it before using NX.  Some first-generation
Intel x86-64 processors didn't support NX, and even recent systems
allow it to be disabled in BIOS.

[ Impact: prevent Xen crash on NX-less 64-bit machines ]

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 arch/x86/mm/Makefile     |    1 +
 arch/x86/xen/enlighten.c |   10 +++++-----
 2 files changed, 6 insertions(+), 5 deletions(-)

--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -4,6 +4,7 @@ obj-y	:=  init.o init_$(BITS).o fault.o 
 # Make sure __phys_addr has no stackprotector
 nostackp := $(call cc-option, -fno-stack-protector)
 CFLAGS_ioremap.o		:= $(nostackp)
+CFLAGS_init.o			:= $(nostackp)
 
 obj-$(CONFIG_SMP)		+= tlb.o
 
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1083,6 +1083,11 @@ asmlinkage void __init xen_start_kernel(
 
 	__supported_pte_mask |= _PAGE_IOMAP;
 
+#ifdef CONFIG_X86_64
+	/* Work out if we support NX */
+	check_efer();
+#endif
+
 	xen_setup_features();
 
 	/* Get mfn list */
@@ -1123,11 +1128,6 @@ asmlinkage void __init xen_start_kernel(
 
 	pgd = (pgd_t *)xen_start_info->pt_base;
 
-#ifdef CONFIG_X86_64
-	/* Work out if we support NX */
-	check_efer();
-#endif
-
 	/* Don't do the full vcpu_info placement stuff until we have a
 	   possible map and a non-dummy shared_info. */
 	per_cpu(xen_vcpu, 0) = &HYPERVISOR_shared_info->vcpu_info[0];


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