From e5fbe20cc7eafe7f53f1a5e01c678a887c02494d Mon Sep 17 00:00:00 2001
From: kettenis <kettenis@openbsd.org>
Date: Sun, 26 Apr 2015 09:48:29 +0000
Subject: [PATCH] Only enable PAE if the CPU we're running on has NX support. 
 Without NX support we're only wasting memory on the larger PAE page tables
 without any real benefit.  This allows some simplifications of the low-level
 assembly code.

ok mlarkin@, deraadt@
---
 sys/arch/i386/i386/locore.s  | 20 ++++----------------
 sys/arch/i386/i386/mptramp.s | 14 +-------------
 sys/arch/i386/i386/pmapae.c  | 17 ++++++++---------
 3 files changed, 13 insertions(+), 38 deletions(-)

diff --git a/sys/arch/i386/i386/locore.s b/sys/arch/i386/i386/locore.s
index 1e8b4d159a6..cea9a8437ba 100644
--- a/sys/arch/i386/i386/locore.s
+++ b/sys/arch/i386/i386/locore.s
@@ -1,4 +1,4 @@
-/*	$OpenBSD: locore.s,v 1.156 2015/04/25 21:31:24 guenther Exp $	*/
+/*	$OpenBSD: locore.s,v 1.157 2015/04/26 09:48:29 kettenis Exp $	*/
 /*	$NetBSD: locore.s,v 1.145 1996/05/03 19:41:19 christos Exp $	*/
 
 /*-
@@ -1660,7 +1660,7 @@ ENTRY(i686_pagezero)
 ENTRY(cpu_paenable)
 	movl	$-1, %eax
 	testl	$CPUID_PAE, _C_LABEL(cpu_feature)
-	jz	2f
+	jz	1f
 
 	pushl	%esi
 	pushl	%edi
@@ -1677,21 +1677,9 @@ ENTRY(cpu_paenable)
 	orl	$CR4_PAE, %eax
 	movl	%eax, %cr4      /* BANG!!! */
 
-	movl	$MSR_EFER,%ecx
+	movl	$MSR_EFER, %ecx
 	rdmsr
-	movl	%edx, %edi		# %edx is needed by wrmsr below
-
-	# Check if we need to enable NXE
-	movl	$0x80000001, %eax
-	cpuid
-	andl	$CPUID_NXE, %edx
-	xorl	%eax,%eax
-	testl	%edx, %edx
-	jz	1f
 	orl	$EFER_NXE, %eax
-1:
-	movl	%edi, %edx		# Restore saved %edx
-	movl	$MSR_EFER,%ecx
 	wrmsr
 
 	movl	12(%esp), %eax
@@ -1703,7 +1691,7 @@ ENTRY(cpu_paenable)
 	xorl	%eax, %eax
 	popl	%edi
 	popl	%esi
-2:
+1:
 	ret
 
 /*
diff --git a/sys/arch/i386/i386/mptramp.s b/sys/arch/i386/i386/mptramp.s
index a6e80b8c9cb..3a5ca00a797 100644
--- a/sys/arch/i386/i386/mptramp.s
+++ b/sys/arch/i386/i386/mptramp.s
@@ -1,4 +1,4 @@
-/*	$OpenBSD: mptramp.s,v 1.16 2015/04/24 12:52:38 kettenis Exp $	*/
+/*	$OpenBSD: mptramp.s,v 1.17 2015/04/26 09:48:29 kettenis Exp $	*/
 
 /*-
  * Copyright (c) 2000 The NetBSD Foundation, Inc.
@@ -170,19 +170,7 @@ _TRMP_LABEL(mp_startup)
 	
 	movl	$MSR_EFER,%ecx
 	rdmsr
-	movl	%edx, %edi		# %edx is needed by wrmsr below
-
-	# Check if we need to enable NXE
-	movl	$0x80000001, %eax
-	cpuid
-	andl	$CPUID_NXE, %edx
-	xorl	%eax,%eax
-	testl	%edx, %edx
-	jz	1f
 	orl	$EFER_NXE, %eax
-1:
-	movl	%edi, %edx		# Restore saved %edx
-	movl	$MSR_EFER,%ecx
 	wrmsr
 
 nopae:
diff --git a/sys/arch/i386/i386/pmapae.c b/sys/arch/i386/i386/pmapae.c
index 44fab2f05ee..28c7aa17004 100644
--- a/sys/arch/i386/i386/pmapae.c
+++ b/sys/arch/i386/i386/pmapae.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: pmapae.c,v 1.35 2015/04/24 19:41:58 kettenis Exp $	*/
+/*	$OpenBSD: pmapae.c,v 1.36 2015/04/26 09:48:29 kettenis Exp $	*/
 
 /*
  * Copyright (c) 2006-2008 Michael Shalayeff
@@ -411,6 +411,8 @@
 typedef u_int64_t pd_entry_t;		/* PDE */
 typedef u_int64_t pt_entry_t;		/* PTE */
 
+#define PG_NX	0x8000000000000000ULL	/* execute-disable */
+
 /*
  * Number of PTEs per cache line. 8 byte pte, 64-byte cache line
  * Used to avoid false sharing of cache lines.
@@ -423,7 +425,6 @@ typedef u_int64_t pt_entry_t;		/* PTE */
 
 extern u_int32_t protection_codes[];	/* maps MI prot to i386 prot code */
 extern boolean_t pmap_initialized;	/* pmap_init done yet? */
-pt_entry_t pg_nx;
 
 /*
  * MULTIPROCESSOR: special VA's/ PTE's are actually allocated inside a
@@ -581,7 +582,7 @@ pmap_pte_paddr_pae(vaddr_t va)
  * Switch over to PAE page tables
  */
 void
-pmap_bootstrap_pae()
+pmap_bootstrap_pae(void)
 {
 	extern int cpu_pae, nkpde;
 	struct pmap *kpm = pmap_kernel();
@@ -591,13 +592,11 @@ pmap_bootstrap_pae()
 	vaddr_t va, eva;
 	int i, pn, pe;
 
-	if (!(cpu_feature & CPUID_PAE)){
+	if ((cpu_feature & CPUID_PAE) == 0 ||
+	    (ecpu_feature & CPUID_NXE) == 0)
 		return;
-	}
 
 	cpu_pae = 1;
-	if (ecpu_feature & CPUID_NXE)
-		pg_nx = (1ULL << 63);
 
 	va = (vaddr_t)kpm->pm_pdir;
 	kpm->pm_pdidx[0] = (va + 0*NBPG - KERNBASE) | PG_V;
@@ -1353,7 +1352,7 @@ pmap_write_protect_pae(struct pmap *pmap, vaddr_t sva, vaddr_t eva,
 
 		md_prot = protection_codes[prot];
 		if (!(prot & PROT_EXEC))
-			md_prot |= pg_nx;
+			md_prot |= PG_NX;
 		if (va < VM_MAXUSER_ADDRESS)
 			md_prot |= PG_u;
 		else if (va < VM_MAX_ADDRESS)
@@ -1610,7 +1609,7 @@ enter_now:
 
 	npte = pa | protection_codes[prot] | PG_V;
 	if (!(prot & PROT_EXEC))
-		npte |= pg_nx;
+		npte |= PG_NX;
 	pmap_exec_account(pmap, va, opte, npte);
 	if (wired)
 		npte |= PG_W;
-- 
2.20.1