x86, mtrr: Constify struct mtrr_ops

This is part of the ops structure constification
effort started by Arjan van de Ven et al.

Benefits of this constification:

 * prevents modification of data that is shared
   (referenced) by many other structure instances
   at runtime

 * detects/prevents accidental (but not intentional)
   modification attempts on archs that enforce
   read-only kernel data at runtime

 * potentially better optimized code as the compiler
   can assume that the const data cannot be changed

 * the compiler/linker move const data into .rodata
   and therefore exclude them from false sharing
Signed-off-by: Emese Revfy <re.emese@gmail.com>
LKML-Reference: <4B65D712.3080804@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/kernel/cpu/mtrr/amd.c

@@ -108,7 +108,7 @@ amd_validate_add_page(unsigned long base, unsigned long size, unsigned int type)
 	return 0;
 }
 
-static struct mtrr_ops amd_mtrr_ops = {
+static const struct mtrr_ops amd_mtrr_ops = {
 	.vendor            = X86_VENDOR_AMD,
 	.set               = amd_set_mtrr,
 	.get               = amd_get_mtrr,

arch/x86/kernel/cpu/mtrr/centaur.c

@@ -110,7 +110,7 @@ centaur_validate_add_page(unsigned long base, unsigned long size, unsigned int t
 	return 0;
 }
 
-static struct mtrr_ops centaur_mtrr_ops = {
+static const struct mtrr_ops centaur_mtrr_ops = {
 	.vendor            = X86_VENDOR_CENTAUR,
 	.set               = centaur_set_mcr,
 	.get               = centaur_get_mcr,

arch/x86/kernel/cpu/mtrr/cyrix.c

@@ -265,7 +265,7 @@ static void cyrix_set_all(void)
 	post_set();
 }
 
-static struct mtrr_ops cyrix_mtrr_ops = {
+static const struct mtrr_ops cyrix_mtrr_ops = {
 	.vendor            = X86_VENDOR_CYRIX,
 	.set_all	   = cyrix_set_all,
 	.set               = cyrix_set_arr,

arch/x86/kernel/cpu/mtrr/generic.c

@@ -752,7 +752,7 @@ int positive_have_wrcomb(void)
 /*
  * Generic structure...
  */
-struct mtrr_ops generic_mtrr_ops = {
+const struct mtrr_ops generic_mtrr_ops = {
 	.use_intel_if		= 1,
 	.set_all		= generic_set_all,
 	.get			= generic_get_mtrr,

arch/x86/kernel/cpu/mtrr/main.c

@@ -60,14 +60,14 @@ static DEFINE_MUTEX(mtrr_mutex);
 u64 size_or_mask, size_and_mask;
 static bool mtrr_aps_delayed_init;
 
-static struct mtrr_ops *mtrr_ops[X86_VENDOR_NUM];
+static const struct mtrr_ops *mtrr_ops[X86_VENDOR_NUM];
 
-struct mtrr_ops *mtrr_if;
+const struct mtrr_ops *mtrr_if;
 
 static void set_mtrr(unsigned int reg, unsigned long base,
 		     unsigned long size, mtrr_type type);
 
-void set_mtrr_ops(struct mtrr_ops *ops)
+void set_mtrr_ops(const struct mtrr_ops *ops)
 {
 	if (ops->vendor && ops->vendor < X86_VENDOR_NUM)
 		mtrr_ops[ops->vendor] = ops;

arch/x86/kernel/cpu/mtrr/mtrr.h

@@ -32,7 +32,7 @@ extern int generic_get_free_region(unsigned long base, unsigned long size,
 extern int generic_validate_add_page(unsigned long base, unsigned long size,
 				     unsigned int type);
 
-extern struct mtrr_ops generic_mtrr_ops;
+extern const struct mtrr_ops generic_mtrr_ops;
 
 extern int positive_have_wrcomb(void);
 
@@ -53,10 +53,10 @@ void fill_mtrr_var_range(unsigned int index,
 		u32 base_lo, u32 base_hi, u32 mask_lo, u32 mask_hi);
 void get_mtrr_state(void);
 
-extern void set_mtrr_ops(struct mtrr_ops *ops);
+extern void set_mtrr_ops(const struct mtrr_ops *ops);
 
 extern u64 size_or_mask, size_and_mask;
-extern struct mtrr_ops *mtrr_if;
+extern const struct mtrr_ops *mtrr_if;
 
 #define is_cpu(vnd)	(mtrr_if && mtrr_if->vendor == X86_VENDOR_##vnd)
 #define use_intel()	(mtrr_if && mtrr_if->use_intel_if == 1)