Message-Id: <200804290352.33543.yhlu.kernel@gmail.com>
Date:	Tue, 29 Apr 2008 03:52:33 -0700
From:	Yinghai Lu <yhlu.kernel.send@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Gabriel C <nix.or.die@...glemail.com>,
	Mika Fischer <mika.fischer@...pnet.de>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/2] x86: mtrr cleanup for converting continuous to discrete layout v8


some BIOS like to use continus MTRR layout, and X driver can not add
WB entries for graphical cards when 4g or more RAM installed.

the patch will change MTRR to discrete.

mtrr_chunk_size= could be used to have smaller continuous block to hold holes.
default is 256m, could be set according to size of graphics card memory.

mtrr_gran_size= could be used to send smallest mtrr block to avoid run out of MTRRs

v2: fix -1 for UC checking
v3: default to disable, and need use enable_mtrr_cleanup to enable this feature
    skip the var state change warning.
    remove next_basek in range_to_mtrr()
v4: correct warning mask.
v5: CONFIG_MTRR_SANITIZER
v6: fix 1g, 2g, 512 aligment with extra hole
v7: gran_sizek to prevent running out of MTRRs.
v8: fix hole_basek caculation caused when removing next_basek
    gran_sizek using when basek is 0.

need to apply
	[PATCH] x86: fix trimming e820 with MTRR holes.
right after this one.

Signed-off-by: Yinghai Lu <yhlu.kernel@...il.com>

Index: linux-2.6/arch/x86/kernel/cpu/mtrr/generic.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/cpu/mtrr/generic.c
+++ linux-2.6/arch/x86/kernel/cpu/mtrr/generic.c
@@ -37,7 +37,7 @@ static struct fixed_range_block fixed_ra
 static unsigned long smp_changes_mask;
 static struct mtrr_state mtrr_state = {};
 static int mtrr_state_set;
-static u64 tom2;
+u64 mtrr_tom2;
 
 #undef MODULE_PARAM_PREFIX
 #define MODULE_PARAM_PREFIX "mtrr."
@@ -139,8 +139,8 @@ u8 mtrr_type_lookup(u64 start, u64 end)
 		}
 	}
 
-	if (tom2) {
-		if (start >= (1ULL<<32) && (end < tom2))
+	if (mtrr_tom2) {
+		if (start >= (1ULL<<32) && (end < mtrr_tom2))
 			return MTRR_TYPE_WRBACK;
 	}
 
@@ -158,6 +158,20 @@ get_mtrr_var_range(unsigned int index, s
 	rdmsr(MTRRphysMask_MSR(index), vr->mask_lo, vr->mask_hi);
 }
 
+/*  fill the MSR pair relating to a var range  */
+void fill_mtrr_var_range(unsigned int index,
+		u32 base_lo, u32 base_hi, u32 mask_lo, u32 mask_hi)
+{
+	struct mtrr_var_range *vr;
+
+	vr = mtrr_state.var_ranges;
+
+	vr[index].base_lo = base_lo;
+	vr[index].base_hi = base_hi;
+	vr[index].mask_lo = mask_lo;
+	vr[index].mask_hi = mask_hi;
+}
+
 static void
 get_fixed_ranges(mtrr_type * frs)
 {
@@ -216,10 +230,10 @@ void __init get_mtrr_state(void)
 		unsigned lo, hi;
 		/* TOP_MEM2 */
 		rdmsr(MSR_K8_TOP_MEM2, lo, hi);
-		tom2 = hi;
-		tom2 <<= 32;
-		tom2 |= lo;
-		tom2 &= 0xffffff8000000ULL;
+		mtrr_tom2 = hi;
+		mtrr_tom2 <<= 32;
+		mtrr_tom2 |= lo;
+		mtrr_tom2 &= 0xffffff8000000ULL;
 	}
 	if (mtrr_show) {
 		int high_width;
@@ -251,9 +265,9 @@ void __init get_mtrr_state(void)
 			else
 				printk(KERN_INFO "MTRR %u disabled\n", i);
 		}
-		if (tom2) {
+		if (mtrr_tom2) {
 			printk(KERN_INFO "TOM2: %016llx aka %lldM\n",
-					  tom2, tom2>>20);
+					  mtrr_tom2, mtrr_tom2>>20);
 		}
 	}
 	mtrr_state_set = 1;
Index: linux-2.6/arch/x86/kernel/cpu/mtrr/main.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/cpu/mtrr/main.c
+++ linux-2.6/arch/x86/kernel/cpu/mtrr/main.c
@@ -37,6 +37,7 @@
 #include <linux/smp.h>
 #include <linux/cpu.h>
 #include <linux/mutex.h>
+#include <linux/sort.h>
 
 #include <asm/e820.h>
 #include <asm/mtrr.h>
@@ -609,6 +610,452 @@ static struct sysdev_driver mtrr_sysdev_
 	.resume		= mtrr_restore,
 };
 
+#ifdef CONFIG_MTRR_SANITIZER
+
+#ifdef CONFIG_MTRR_SANITIZER_ENABLE_DEFAULT
+static int enable_mtrr_cleanup __initdata = 1;
+#else
+static int enable_mtrr_cleanup __initdata;
+#endif
+
+#else
+
+static int enable_mtrr_cleanup __initdata = -1;
+
+#endif
+
+static int __init disable_mtrr_cleanup_setup(char *str)
+{
+	if (enable_mtrr_cleanup != -1)
+		enable_mtrr_cleanup = 0;
+	return 0;
+}
+early_param("disable_mtrr_cleanup", disable_mtrr_cleanup_setup);
+
+static int __init enable_mtrr_cleanup_setup(char *str)
+{
+	if (enable_mtrr_cleanup != -1)
+		enable_mtrr_cleanup = 1;
+	return 0;
+}
+early_param("enble_mtrr_cleanup", enable_mtrr_cleanup_setup);
+
+#define RANGE_NUM 256
+
+struct res_range {
+	unsigned long start;
+	unsigned long end;
+};
+
+static int __init add_range(struct res_range *range, int nr_range, unsigned long start,
+			      unsigned long end, int merge)
+{
+	int i;
+
+	if (!merge)
+		goto addit;
+
+	/* try to merge it with old one */
+	for (i = 0; i < nr_range; i++) {
+		unsigned long final_start, final_end;
+		unsigned long common_start, common_end;
+
+		if (!range[i].end)
+			continue;
+
+		common_start = max(range[i].start, start);
+		common_end = min(range[i].end, end);
+		if (common_start > common_end + 1)
+			continue;
+
+		final_start = min(range[i].start, start);
+		final_end = max(range[i].end, end);
+
+		range[i].start = final_start;
+		range[i].end =  final_end;
+		return nr_range;
+	}
+
+addit:
+	/* need to add that */
+	if (nr_range >= RANGE_NUM)
+		return nr_range;
+
+	range[nr_range].start = start;
+	range[nr_range].end = end;
+
+	nr_range++;
+
+	return nr_range;
+
+}
+static void __init subtract_range(struct res_range *range, unsigned long start,
+				unsigned long end)
+{
+	int i;
+	int j;
+
+	for (j = 0; j < RANGE_NUM; j++) {
+		if (!range[j].end)
+			continue;
+
+		if (start <= range[j].start && end >= range[j].end) {
+			range[j].start = 0;
+			range[j].end = 0;
+			continue;
+		}
+
+		if (start <= range[j].start && end < range[j].end && range[j].start < end + 1) {
+			range[j].start = end + 1;
+			continue;
+		}
+
+
+		if (start > range[j].start && end >= range[j].end && range[j].end > start - 1) {
+			range[j].end = start - 1;
+			continue;
+		}
+
+		if (start > range[j].start && end < range[j].end) {
+			/* find the new spare */
+			for (i = 0; i < RANGE_NUM; i++) {
+				if (range[i].end == 0)
+					break;
+			}
+			if (i < RANGE_NUM) {
+				range[i].end = range[j].end;
+				range[i].start = end + 1;
+			} else {
+				printk(KERN_ERR "run of slot in ranges\n");
+			}
+			range[j].end = start - 1;
+			continue;
+		}
+	}
+}
+
+static int __init cmp_range(const void *x1, const void *x2)
+{
+	const struct res_range *r1 = x1;
+	const struct res_range *r2 = x2;
+	long start1, start2;
+
+	start1 = r1->start;
+	start2 = r2->start;
+
+	return start1 - start2;
+}
+
+struct var_mtrr_state {
+	unsigned long range_startk, range_sizek;
+	unsigned long chunk_sizek;
+	unsigned long gran_sizek;
+	unsigned int reg;
+	unsigned address_bits;
+};
+
+static void __init set_var_mtrr(
+	unsigned int reg, unsigned long basek, unsigned long sizek,
+	unsigned char type, unsigned address_bits)
+{
+	u32 base_lo, base_hi, mask_lo, mask_hi;
+	unsigned address_mask_high;
+
+	if (!sizek) {
+		fill_mtrr_var_range(reg, 0, 0, 0, 0);
+		return;
+	}
+
+	address_mask_high = ((1u << (address_bits - 32u)) - 1u);
+
+	base_hi = basek >> 22;
+	base_lo  = basek << 10;
+
+	if (sizek < 4*1024*1024) {
+		mask_hi = address_mask_high;
+		mask_lo = ~((sizek << 10) - 1);
+	} else {
+		mask_hi = address_mask_high & (~((sizek >> 22) - 1));
+		mask_lo = 0;
+	}
+
+	base_lo |= type;
+	mask_lo |= 0x800;
+	fill_mtrr_var_range(reg, base_lo, base_hi, mask_lo, mask_hi);
+}
+
+static unsigned int __init range_to_mtrr(unsigned int reg,
+	unsigned long range_startk, unsigned long range_sizek,
+	unsigned char type, unsigned address_bits)
+{
+	if (!range_sizek || (reg >= num_var_ranges))
+		return reg;
+
+	while (range_sizek) {
+		unsigned long max_align, align;
+		unsigned long sizek;
+		/* Compute the maximum size I can make a range */
+		if (range_startk)
+			max_align = ffs(range_startk) - 1;
+		else
+			max_align = 32;
+		align = fls(range_sizek) - 1;
+		if (align > max_align)
+			align = max_align;
+
+		sizek = 1 << align;
+		printk(KERN_INFO "Setting variable MTRR %d, base: %ldMB, range: %ldMB, type %s\n",
+			reg, range_startk >> 10, sizek >> 10,
+			(type == MTRR_TYPE_UNCACHABLE)?"UC":
+			    ((type == MTRR_TYPE_WRBACK)?"WB":"Other")
+			);
+		set_var_mtrr(reg++, range_startk, sizek, type, address_bits);
+		range_startk += sizek;
+		range_sizek -= sizek;
+		if (reg >= num_var_ranges)
+			break;
+	}
+	return reg;
+}
+
+static void __init range_to_mtrr_with_hole(struct var_mtrr_state *state, unsigned long basek)
+{
+	unsigned long hole_basek, hole_sizek;
+	unsigned long range0_basek, range0_sizek;
+	unsigned long range_basek, range_sizek;
+	unsigned long chunk_sizek;
+	unsigned long gran_sizek;
+
+	hole_basek = 0;
+	hole_sizek = 0;
+	chunk_sizek = state->chunk_sizek;
+	gran_sizek = state->gran_sizek;
+
+	/* align with gran size, prevent small block used up MTRRs */
+	range_basek = ALIGN(state->range_startk, gran_sizek);
+	if ((range_basek > basek) && basek)
+		return;
+	range_sizek = ALIGN(state->range_sizek - (range_basek - state->range_startk), gran_sizek);
+
+	while (range_basek + range_sizek > (state->range_startk + state->range_sizek)) {
+		range_sizek -= gran_sizek;
+		if (!range_sizek)
+			return;
+	}
+	state->range_startk = range_basek;
+	state->range_sizek = range_sizek;
+
+	/* try to append some small hole */
+	range0_basek = state->range_startk;
+	range0_sizek = ALIGN(state->range_sizek, chunk_sizek);
+	if ((range0_sizek == state->range_sizek) ||
+	    ((range0_basek + range0_sizek - chunk_sizek > basek) && basek)) {
+			printk(KERN_INFO "rangeX: %016lx - %016lx\n", range0_basek<<10, (range0_basek + state->range_sizek)<<10);
+			state->reg = range_to_mtrr(state->reg, range0_basek,
+				state->range_sizek, MTRR_TYPE_WRBACK, state->address_bits);
+		return;
+	}
+
+
+	range0_sizek -= chunk_sizek;
+	printk(KERN_INFO "range0: %016lx - %016lx\n", range0_basek<<10, (range0_basek + range0_sizek)<<10);
+	state->reg = range_to_mtrr(state->reg, range0_basek,
+			range0_sizek, MTRR_TYPE_WRBACK, state->address_bits);
+
+	range_basek = range0_basek + range0_sizek;
+	range_sizek = chunk_sizek;
+	if (range_sizek - (state->range_sizek - range0_sizek) < (chunk_sizek >> 1)) {
+		hole_sizek = range_sizek - (state->range_sizek - range0_sizek);
+		hole_basek = range_basek + range_sizek - hole_sizek;
+	} else
+		range_sizek = state->range_sizek - range0_sizek;
+
+	printk(KERN_INFO "range: %016lx - %016lx\n", range_basek<<10, (range_basek + range_sizek)<<10);
+	state->reg = range_to_mtrr(state->reg, range_basek,
+			range_sizek, MTRR_TYPE_WRBACK, state->address_bits);
+	if (hole_sizek) {
+		printk(KERN_INFO "hole: %016lx - %016lx\n", hole_basek<<10, (hole_basek + hole_sizek)<<10);
+		state->reg = range_to_mtrr(state->reg, hole_basek,
+				hole_sizek, MTRR_TYPE_UNCACHABLE, state->address_bits);
+	}
+}
+
+static void __init set_var_mtrr_range(struct var_mtrr_state *state, unsigned long base_pfn, unsigned long size_pfn)
+{
+	unsigned long basek, sizek;
+
+	if (state->reg >= num_var_ranges)
+		return;
+
+	basek = base_pfn << (PAGE_SHIFT - 10);
+	sizek = size_pfn << (PAGE_SHIFT - 10);
+
+	/* See if I can merge with the last range */
+	if ((basek <= 1024) || (state->range_startk + state->range_sizek == basek)) {
+		unsigned long endk = basek + sizek;
+		state->range_sizek = endk - state->range_startk;
+		return;
+	}
+	/* Write the range mtrrs */
+	if (state->range_sizek != 0) {
+		range_to_mtrr_with_hole(state, basek);
+
+		state->range_startk = 0;
+		state->range_sizek = 0;
+	}
+	/* Allocate an msr */
+	state->range_startk = basek;
+	state->range_sizek  = sizek;
+}
+
+/* mininum size of mtrr block that can take hole */
+static u64 mtrr_chunk_size __initdata = (256ULL<<20);
+
+static int __init parse_mtrr_chunk_size_opt(char *p)
+{
+	if (!p)
+		return -EINVAL;
+	mtrr_chunk_size = memparse(p, &p);
+	return 0;
+}
+early_param("mtrr_chunk_size", parse_mtrr_chunk_size_opt);
+
+/* granity of mtrr of block */
+static u64 mtrr_gran_size __initdata = (64ULL<<20);
+
+static int __init parse_mtrr_gran_size_opt(char *p)
+{
+	if (!p)
+		return -EINVAL;
+	mtrr_gran_size = memparse(p, &p);
+	return 0;
+}
+early_param("mtrr_gran_size", parse_mtrr_gran_size_opt);
+
+static void __init x86_setup_var_mtrrs(struct res_range *range, int nr_range, unsigned address_bits)
+{
+	struct var_mtrr_state var_state;
+	int i;
+
+	var_state.range_startk = 0;
+	var_state.range_sizek = 0;
+	var_state.reg = 0;
+	var_state.address_bits = address_bits;
+	var_state.chunk_sizek = mtrr_chunk_size >> 10;
+	var_state.gran_sizek = mtrr_gran_size >> 10;
+
+	/* Write the range etc */
+	for (i = 0; i < nr_range; i++)
+		set_var_mtrr_range(&var_state, range[i].start, range[i].end - range[i].start + 1);
+
+	/* Write the last range */
+	range_to_mtrr_with_hole(&var_state, 0);
+	printk(KERN_INFO "DONE variable MTRRs\n");
+	/* Clear out the extra MTRR's */
+	while (var_state.reg < num_var_ranges)
+		set_var_mtrr(var_state.reg++, 0, 0, 0, var_state.address_bits);
+}
+
+static int __init x86_get_mtrr_mem_range(struct res_range *range, int nr_range, unsigned long extra_remove_base, unsigned long extra_remove_size)
+{
+	unsigned long i, base, size;
+	mtrr_type type;
+
+	for (i = 0; i < num_var_ranges; i++) {
+		mtrr_if->get(i, &base, &size, &type);
+		if (type != MTRR_TYPE_WRBACK)
+			continue;
+		nr_range = add_range(range, nr_range, base, base + size - 1, 1);
+	}
+	printk(KERN_INFO "After WB checking\n");
+	for (i = 0; i < nr_range; i++)
+		printk(KERN_INFO "MTRR MAP PFN: %016lx - %016lx\n", range[i].start, range[i].end + 1);
+
+	/* take out UC ranges */
+	for (i = 0; i < num_var_ranges; i++) {
+		mtrr_if->get(i, &base, &size, &type);
+		if (type != MTRR_TYPE_UNCACHABLE)
+			continue;
+		if (!size)
+			continue;
+		subtract_range(range, base, base + size - 1);
+	}
+	if (extra_remove_size)
+		subtract_range(range, extra_remove_base,  extra_remove_base + extra_remove_size  - 1);
+
+	/* get new range num */
+	nr_range = 0;
+	for (i = 0; i < RANGE_NUM; i++) {
+		if (!range[i].end)
+			continue;
+		nr_range++;
+	}
+	printk(KERN_INFO "After UC checking\n");
+	for (i = 0; i < nr_range; i++)
+		printk(KERN_INFO "MTRR MAP PFN: %016lx - %016lx\n", range[i].start, range[i].end + 1);
+
+	/* sort the ranges */
+	sort(range, nr_range, sizeof(struct res_range), cmp_range, NULL);
+	printk(KERN_INFO "After sorting\n");
+	for (i = 0; i < nr_range; i++)
+		printk(KERN_INFO "MTRR MAP PFN: %016lx - %016lx\n", range[i].start, range[i].end + 1);
+
+	return nr_range;
+}
+
+static int __init mtrr_cleanup(unsigned address_bits)
+{
+	unsigned long i, base, size, def, dummy;
+	mtrr_type type;
+	struct res_range range[RANGE_NUM];
+	int nr_range;
+	unsigned long extra_remove_base, extra_remove_size;
+
+	/* extra one for all 0 */
+	int num[MTRR_NUM_TYPES + 1];
+
+	if (!is_cpu(INTEL) || enable_mtrr_cleanup < 1)
+		return 0;
+	rdmsr(MTRRdefType_MSR, def, dummy);
+	def &= 0xff;
+	if (def != MTRR_TYPE_UNCACHABLE)
+		return 0;
+
+	/* check entries number */
+	memset(num, 0, sizeof(num));
+	for (i = 0; i < num_var_ranges; i++) {
+		mtrr_if->get(i, &base, &size, &type);
+		if (type >= MTRR_NUM_TYPES)
+			continue;
+		if (!size)
+			type = MTRR_NUM_TYPES;
+		num[type]++;
+	}
+
+	/* check if we got UC entries */
+	if (!num[MTRR_TYPE_UNCACHABLE])
+		return 0;
+
+	/* check if we only had WB and UC */
+	if (num[MTRR_TYPE_WRBACK] + num[MTRR_TYPE_UNCACHABLE] !=
+		num_var_ranges - num[MTRR_NUM_TYPES])
+		return 0;
+
+	memset(range, 0, sizeof(range));
+	extra_remove_size = 0;
+	if (mtrr_tom2) {
+		extra_remove_base = 1 << (32 - PAGE_SHIFT);
+		extra_remove_size = (mtrr_tom2>>PAGE_SHIFT) - extra_remove_base;
+	}
+	nr_range = x86_get_mtrr_mem_range(range, 0, extra_remove_base, extra_remove_size);
+
+	/* convert ranges to var ranges state */
+	x86_setup_var_mtrrs(range, nr_range, address_bits);
+
+	return 1;
+
+}
+
 static int disable_mtrr_trim;
 
 static int __init disable_mtrr_trim_setup(char *str)
@@ -729,18 +1176,21 @@ int __init mtrr_trim_uncached_memory(uns
  */
 void __init mtrr_bp_init(void)
 {
+	u32 phys_addr;
 	init_ifs();
 
+	phys_addr = 32;
+
 	if (cpu_has_mtrr) {
 		mtrr_if = &generic_mtrr_ops;
 		size_or_mask = 0xff000000;	/* 36 bits */
 		size_and_mask = 0x00f00000;
+		phys_addr = 36;
 
 		/* This is an AMD specific MSR, but we assume(hope?) that
 		   Intel will implement it to when they extend the address
 		   bus of the Xeon. */
 		if (cpuid_eax(0x80000000) >= 0x80000008) {
-			u32 phys_addr;
 			phys_addr = cpuid_eax(0x80000008) & 0xff;
 			/* CPUID workaround for Intel 0F33/0F34 CPU */
 			if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
@@ -758,6 +1208,7 @@ void __init mtrr_bp_init(void)
 			   don't support PAE */
 			size_or_mask = 0xfff00000;	/* 32 bits */
 			size_and_mask = 0;
+			phys_addr = 32;
 		}
 	} else {
 		switch (boot_cpu_data.x86_vendor) {
@@ -791,8 +1242,13 @@ void __init mtrr_bp_init(void)
 	if (mtrr_if) {
 		set_num_var_ranges();
 		init_table();
-		if (use_intel())
+		if (use_intel()) {
 			get_mtrr_state();
+
+			if (mtrr_cleanup(phys_addr))
+				mtrr_if->set_all();
+
+		}
 	}
 }
 
@@ -829,9 +1285,10 @@ static int __init mtrr_init_finialize(vo
 {
 	if (!mtrr_if)
 		return 0;
-	if (use_intel())
-		mtrr_state_warn();
-	else {
+	if (use_intel()) {
+		if (enable_mtrr_cleanup < 1)
+			mtrr_state_warn();
+	} else {
 		/* The CPUs haven't MTRR and seem to not support SMP. They have
 		 * specific drivers, we use a tricky method to support
 		 * suspend/resume for them.
Index: linux-2.6/arch/x86/kernel/cpu/mtrr/mtrr.h
===================================================================
--- linux-2.6.orig/arch/x86/kernel/cpu/mtrr/mtrr.h
+++ linux-2.6/arch/x86/kernel/cpu/mtrr/mtrr.h
@@ -81,6 +81,8 @@ void set_mtrr_done(struct set_mtrr_conte
 void set_mtrr_cache_disable(struct set_mtrr_context *ctxt);
 void set_mtrr_prepare_save(struct set_mtrr_context *ctxt);
 
+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);
@@ -92,6 +94,7 @@ extern struct mtrr_ops * mtrr_if;
 #define use_intel()	(mtrr_if && mtrr_if->use_intel_if == 1)
 
 extern unsigned int num_var_ranges;
+extern u64 mtrr_tom2;
 
 void mtrr_state_warn(void);
 const char *mtrr_attrib_to_str(int x);
Index: linux-2.6/Documentation/kernel-parameters.txt
===================================================================
--- linux-2.6.orig/Documentation/kernel-parameters.txt
+++ linux-2.6/Documentation/kernel-parameters.txt
@@ -595,6 +595,20 @@ and is between 256 and 4096 characters. 
 			See drivers/char/README.epca and
 			Documentation/digiepca.txt.
 
+	disable_mtrr_cleanup [X86]
+	enable_mtrr_cleanup [X86]
+			The kernel tries to adjust MTRR layout from continuous
+			to discrete, to make X server driver able to add WB
+			entry later. This parameter enables/disables that.
+
+	mtrr_chunk_size=nn[KMG] [X86]
+			used for mtrr cleanup. It is largest continous chunk
+			that could hold holes aka. UC entries.
+
+	mtrr_gran_size=nn[KMG] [X86]
+			used for mtrr cleanup. It is granity of mtrr block.
+			Big value could prevent small alignment use up MTRRs.
+
 	disable_mtrr_trim [X86, Intel and AMD only]
 			By default the kernel will trim any uncacheable
 			memory out of your available memory pool based on
Index: linux-2.6/arch/x86/Kconfig
===================================================================
--- linux-2.6.orig/arch/x86/Kconfig
+++ linux-2.6/arch/x86/Kconfig
@@ -1035,6 +1035,32 @@ config MTRR
 
 	  See <file:Documentation/mtrr.txt> for more information.
 
+config MTRR_SANITIZER
+	def_bool y
+	prompt "MTRR cleanup support"
+	depends on MTRR
+	help
+	  Convert MTRR layout from continuous to discrete, so some X driver
+	  could add WB entries.
+
+	  Say N here if you see bootup problems (boot crash, boot hang,
+	  spontaneous reboots).
+
+	  Could be disabled with disable_mtrr_cleanup. Also mtrr_chunk_size
+	  could be used to send largest mtrr entry size for continuous block
+	  to hold holes (aka. UC entries)
+
+	  If unsure, say Y.
+
+config MTRR_SANITIZER_ENABLE_DEFAULT
+	def_bool y
+	prompt "Enable MTRR cleanup by default"
+	depends on MTRR_SANITIZER
+	help
+	  Enable mtrr cleanup by default
+
+	  If unsure, say Y.
+
 config X86_PAT
 	bool
 	prompt "x86 PAT support"
--
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