x86, mm: Clean up and simplify NX enablement

The 32- and 64-bit code used very different mechanisms for enabling
NX, but even the 32-bit code was enabling NX in head_32.S if it is
available.  Furthermore, we had a bewildering collection of tests for
the available of NX.

This patch:

a) merges the 32-bit set_nx() and the 64-bit check_efer() function
   into a single x86_configure_nx() function.  EFER control is left
   to the head code.

b) eliminates the nx_enabled variable entirely.  Things that need to
   test for NX enablement can verify __supported_pte_mask directly,
   and cpu_has_nx gives the supported status of NX.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Vegard Nossum <vegardno@ifi.uio.no>
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Chris Wright <chrisw@sous-sol.org>
LKML-Reference: <1258154897-6770-5-git-send-email-hpa@zytor.com>
Acked-by: Kees Cook <kees.cook@canonical.com>

2 files changed, 8 insertions, 39 deletions

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 73ffd5536f62..27ec2c23fd47 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -146,8 +146,8 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
         use_gbpages = direct_gbpages;
 #endif
 
-        set_nx();
-        if (nx_enabled)
+        /* XXX: replace this with Kees' improved messages */
+        if (__supported_pte_mask & _PAGE_NX)
                 printk(KERN_INFO "NX (Execute Disable) protection: active\n");
 
         /* Enable PSE if available */
diff --git a/arch/x86/mm/setup_nx.c b/arch/x86/mm/setup_nx.c
index 513d8ed5d2ec..355818b087b5 100644
--- a/arch/x86/mm/setup_nx.c
+++ b/arch/x86/mm/setup_nx.c
@@ -3,10 +3,8 @@
 #include <linux/init.h>
 
 #include <asm/pgtable.h>
+#include <asm/proto.h>
 
-int nx_enabled;
-
-#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
 static int disable_nx __cpuinitdata;
 
 /*
@@ -22,48 +20,19 @@ static int __init noexec_setup(char *str)
         if (!str)
                 return -EINVAL;
         if (!strncmp(str, "on", 2)) {
-                __supported_pte_mask |= _PAGE_NX;
                 disable_nx = 0;
         } else if (!strncmp(str, "off", 3)) {
                 disable_nx = 1;
-                __supported_pte_mask &= ~_PAGE_NX;
         }
+        x86_configure_nx();
         return 0;
 }
 early_param("noexec", noexec_setup);
-#endif
-
-#ifdef CONFIG_X86_PAE
-void __init set_nx(void)
-{
-        unsigned int v[4], l, h;
-
-        if (cpu_has_pae && (cpuid_eax(0x80000000) > 0x80000001)) {
-                cpuid(0x80000001, &v[0], &v[1], &v[2], &v[3]);
-
-                if ((v[3] & (1 << 20)) && !disable_nx) {
-                        rdmsr(MSR_EFER, l, h);
-                        l |= EFER_NX;
-                        wrmsr(MSR_EFER, l, h);
-                        nx_enabled = 1;
-                        __supported_pte_mask |= _PAGE_NX;
-                }
-        }
-}
-#else
-void set_nx(void)
-{
-}
-#endif
 
-#ifdef CONFIG_X86_64
-void __cpuinit check_efer(void)
+void __cpuinit x86_configure_nx(void)
 {
-        unsigned long efer;
-
-        rdmsrl(MSR_EFER, efer);
-        if (!(efer & EFER_NX) || disable_nx)
+        if (cpu_has_nx && !disable_nx)
+                __supported_pte_mask |= _PAGE_NX;
+        else
                 __supported_pte_mask &= ~_PAGE_NX;
 }
-#endif
-