xref: /linux/arch/x86/mm/pat/memtype.c (revision 8804d970fab45726b3c7cd7f240b31122aa94219)

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Page Attribute Table (PAT) support: handle memory caching attributes in page tables.
 *
 * Authors: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
 *          Suresh B Siddha <suresh.b.siddha@intel.com>
 *
 * Loosely based on earlier PAT patchset from Eric Biederman and Andi Kleen.
 *
 * Basic principles:
 *
 * PAT is a CPU feature supported by all modern x86 CPUs, to allow the firmware and
 * the kernel to set one of a handful of 'caching type' attributes for physical
 * memory ranges: uncached, write-combining, write-through, write-protected,
 * and the most commonly used and default attribute: write-back caching.
 *
 * PAT support supersedes and augments MTRR support in a compatible fashion: MTRR is
 * a hardware interface to enumerate a limited number of physical memory ranges
 * and set their caching attributes explicitly, programmed into the CPU via MSRs.
 * Even modern CPUs have MTRRs enabled - but these are typically not touched
 * by the kernel or by user-space (such as the X server), we rely on PAT for any
 * additional cache attribute logic.
 *
 * PAT doesn't work via explicit memory ranges, but uses page table entries to add
 * cache attribute information to the mapped memory range: there's 3 bits used,
 * (_PAGE_PWT, _PAGE_PCD, _PAGE_PAT), with the 8 possible values mapped by the
 * CPU to actual cache attributes via an MSR loaded into the CPU (MSR_IA32_CR_PAT).
 *
 * ( There's a metric ton of finer details, such as compatibility with CPU quirks
 *   that only support 4 types of PAT entries, and interaction with MTRRs, see
 *   below for details. )
 */

#include <linux/seq_file.h>
#include <linux/memblock.h>
#include <linux/debugfs.h>
#include <linux/ioport.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/io.h>
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/fs.h>
#include <linux/rbtree.h>

#include <asm/cpu_device_id.h>
#include <asm/cacheflush.h>
#include <asm/cacheinfo.h>
#include <asm/processor.h>
#include <asm/tlbflush.h>
#include <asm/x86_init.h>
#include <asm/fcntl.h>
#include <asm/e820/api.h>
#include <asm/mtrr.h>
#include <asm/page.h>
#include <asm/msr.h>
#include <asm/memtype.h>
#include <asm/io.h>

#include "memtype.h"
#include "../mm_internal.h"

#undef pr_fmt
#define pr_fmt(fmt) "" fmt

static bool __read_mostly pat_disabled = !IS_ENABLED(CONFIG_X86_PAT);
static u64 __ro_after_init pat_msr_val;

/*
 * PAT support is enabled by default, but can be disabled for
 * various user-requested or hardware-forced reasons:
 */
static void __init pat_disable(const char *msg_reason)
{
	if (pat_disabled)
		return;

	pat_disabled = true;
	pr_info("x86/PAT: %s\n", msg_reason);

	memory_caching_control &= ~CACHE_PAT;
}

static int __init nopat(char *str)
{
	pat_disable("PAT support disabled via boot option.");
	return 0;
}
early_param("nopat", nopat);

bool pat_enabled(void)
{
	return !pat_disabled;
}
EXPORT_SYMBOL_GPL(pat_enabled);

int pat_debug_enable;

static int __init pat_debug_setup(char *str)
{
	pat_debug_enable = 1;
	return 1;
}
__setup("debugpat", pat_debug_setup);

#ifdef CONFIG_X86_PAT
/*
 * X86 PAT uses page flags arch_1 and arch_2 together to keep track of
 * memory type of pages that have backing page struct.
 *
 * X86 PAT supports 4 different memory types:
 *  - _PAGE_CACHE_MODE_WB
 *  - _PAGE_CACHE_MODE_WC
 *  - _PAGE_CACHE_MODE_UC_MINUS
 *  - _PAGE_CACHE_MODE_WT
 *
 * _PAGE_CACHE_MODE_WB is the default type.
 */

#define _PGMT_WB		0
#define _PGMT_WC		(1UL << PG_arch_1)
#define _PGMT_UC_MINUS		(1UL << PG_arch_2)
#define _PGMT_WT		(1UL << PG_arch_2 | 1UL << PG_arch_1)
#define _PGMT_MASK		(1UL << PG_arch_2 | 1UL << PG_arch_1)
#define _PGMT_CLEAR_MASK	(~_PGMT_MASK)

static inline enum page_cache_mode get_page_memtype(struct page *pg)
{
	unsigned long pg_flags = pg->flags.f & _PGMT_MASK;

	if (pg_flags == _PGMT_WB)
		return _PAGE_CACHE_MODE_WB;
	else if (pg_flags == _PGMT_WC)
		return _PAGE_CACHE_MODE_WC;
	else if (pg_flags == _PGMT_UC_MINUS)
		return _PAGE_CACHE_MODE_UC_MINUS;
	else
		return _PAGE_CACHE_MODE_WT;
}

static inline void set_page_memtype(struct page *pg,
				    enum page_cache_mode memtype)
{
	unsigned long memtype_flags;
	unsigned long old_flags;
	unsigned long new_flags;

	switch (memtype) {
	case _PAGE_CACHE_MODE_WC:
		memtype_flags = _PGMT_WC;
		break;
	case _PAGE_CACHE_MODE_UC_MINUS:
		memtype_flags = _PGMT_UC_MINUS;
		break;
	case _PAGE_CACHE_MODE_WT:
		memtype_flags = _PGMT_WT;
		break;
	case _PAGE_CACHE_MODE_WB:
	default:
		memtype_flags = _PGMT_WB;
		break;
	}

	old_flags = READ_ONCE(pg->flags.f);
	do {
		new_flags = (old_flags & _PGMT_CLEAR_MASK) | memtype_flags;
	} while (!try_cmpxchg(&pg->flags.f, &old_flags, new_flags));
}
#else
static inline enum page_cache_mode get_page_memtype(struct page *pg)
{
	return -1;
}
static inline void set_page_memtype(struct page *pg,
				    enum page_cache_mode memtype)
{
}
#endif

#define CM(c) (_PAGE_CACHE_MODE_ ## c)

static enum page_cache_mode __init pat_get_cache_mode(unsigned int pat_val,
						      char *msg)
{
	enum page_cache_mode cache;
	char *cache_mode;

	switch (pat_val) {
	case X86_MEMTYPE_UC:       cache = CM(UC);       cache_mode = "UC  "; break;
	case X86_MEMTYPE_WC:       cache = CM(WC);       cache_mode = "WC  "; break;
	case X86_MEMTYPE_WT:       cache = CM(WT);       cache_mode = "WT  "; break;
	case X86_MEMTYPE_WP:       cache = CM(WP);       cache_mode = "WP  "; break;
	case X86_MEMTYPE_WB:       cache = CM(WB);       cache_mode = "WB  "; break;
	case X86_MEMTYPE_UC_MINUS: cache = CM(UC_MINUS); cache_mode = "UC- "; break;
	default:                   cache = CM(WB);       cache_mode = "WB  "; break;
	}

	memcpy(msg, cache_mode, 4);

	return cache;
}

#undef CM

/*
 * Update the cache mode to pgprot translation tables according to PAT
 * configuration.
 * Using lower indices is preferred, so we start with highest index.
 */
static void __init init_cache_modes(u64 pat)
{
	enum page_cache_mode cache;
	char pat_msg[33];
	int i;

	pat_msg[32] = 0;
	for (i = 7; i >= 0; i--) {
		cache = pat_get_cache_mode((pat >> (i * 8)) & 7,
					   pat_msg + 4 * i);
		update_cache_mode_entry(i, cache);
	}
	pr_info("x86/PAT: Configuration [0-7]: %s\n", pat_msg);
}

void pat_cpu_init(void)
{
	if (!boot_cpu_has(X86_FEATURE_PAT)) {
		/*
		 * If this happens we are on a secondary CPU, but switched to
		 * PAT on the boot CPU. We have no way to undo PAT.
		 */
		panic("x86/PAT: PAT enabled, but not supported by secondary CPU\n");
	}

	wrmsrq(MSR_IA32_CR_PAT, pat_msr_val);

	__flush_tlb_all();
}

/**
 * pat_bp_init - Initialize the PAT MSR value and PAT table
 *
 * This function initializes PAT MSR value and PAT table with an OS-defined
 * value to enable additional cache attributes, WC, WT and WP.
 *
 * This function prepares the calls of pat_cpu_init() via cache_cpu_init()
 * on all CPUs.
 */
void __init pat_bp_init(void)
{
	struct cpuinfo_x86 *c = &boot_cpu_data;

	if (!IS_ENABLED(CONFIG_X86_PAT))
		pr_info_once("x86/PAT: PAT support disabled because CONFIG_X86_PAT is disabled in the kernel.\n");

	if (!cpu_feature_enabled(X86_FEATURE_PAT))
		pat_disable("PAT not supported by the CPU.");
	else
		rdmsrq(MSR_IA32_CR_PAT, pat_msr_val);

	if (!pat_msr_val) {
		pat_disable("PAT support disabled by the firmware.");

		/*
		 * No PAT. Emulate the PAT table that corresponds to the two
		 * cache bits, PWT (Write Through) and PCD (Cache Disable).
		 * This setup is also the same as the BIOS default setup.
		 *
		 * PTE encoding:
		 *
		 *       PCD
		 *       |PWT  PAT
		 *       ||    slot
		 *       00    0    WB : _PAGE_CACHE_MODE_WB
		 *       01    1    WT : _PAGE_CACHE_MODE_WT
		 *       10    2    UC-: _PAGE_CACHE_MODE_UC_MINUS
		 *       11    3    UC : _PAGE_CACHE_MODE_UC
		 *
		 * NOTE: When WC or WP is used, it is redirected to UC- per
		 * the default setup in __cachemode2pte_tbl[].
		 */
		pat_msr_val = PAT_VALUE(WB, WT, UC_MINUS, UC, WB, WT, UC_MINUS, UC);
	}

	/*
	 * Xen PV doesn't allow to set PAT MSR, but all cache modes are
	 * supported.
	 */
	if (pat_disabled || cpu_feature_enabled(X86_FEATURE_XENPV)) {
		init_cache_modes(pat_msr_val);
		return;
	}

	if ((c->x86_vfm >= INTEL_PENTIUM_PRO   && c->x86_vfm <= INTEL_PENTIUM_M_DOTHAN) ||
	    (c->x86_vfm >= INTEL_P4_WILLAMETTE && c->x86_vfm <= INTEL_P4_CEDARMILL)) {
		/*
		 * PAT support with the lower four entries. Intel Pentium 2,
		 * 3, M, and 4 are affected by PAT errata, which makes the
		 * upper four entries unusable. To be on the safe side, we don't
		 * use those.
		 *
		 *  PTE encoding:
		 *      PAT
		 *      |PCD
		 *      ||PWT  PAT
		 *      |||    slot
		 *      000    0    WB : _PAGE_CACHE_MODE_WB
		 *      001    1    WC : _PAGE_CACHE_MODE_WC
		 *      010    2    UC-: _PAGE_CACHE_MODE_UC_MINUS
		 *      011    3    UC : _PAGE_CACHE_MODE_UC
		 * PAT bit unused
		 *
		 * NOTE: When WT or WP is used, it is redirected to UC- per
		 * the default setup in __cachemode2pte_tbl[].
		 */
		pat_msr_val = PAT_VALUE(WB, WC, UC_MINUS, UC, WB, WC, UC_MINUS, UC);
	} else {
		/*
		 * Full PAT support.  We put WT in slot 7 to improve
		 * robustness in the presence of errata that might cause
		 * the high PAT bit to be ignored.  This way, a buggy slot 7
		 * access will hit slot 3, and slot 3 is UC, so at worst
		 * we lose performance without causing a correctness issue.
		 * Pentium 4 erratum N46 is an example for such an erratum,
		 * although we try not to use PAT at all on affected CPUs.
		 *
		 *  PTE encoding:
		 *      PAT
		 *      |PCD
		 *      ||PWT  PAT
		 *      |||    slot
		 *      000    0    WB : _PAGE_CACHE_MODE_WB
		 *      001    1    WC : _PAGE_CACHE_MODE_WC
		 *      010    2    UC-: _PAGE_CACHE_MODE_UC_MINUS
		 *      011    3    UC : _PAGE_CACHE_MODE_UC
		 *      100    4    WB : Reserved
		 *      101    5    WP : _PAGE_CACHE_MODE_WP
		 *      110    6    UC-: Reserved
		 *      111    7    WT : _PAGE_CACHE_MODE_WT
		 *
		 * The reserved slots are unused, but mapped to their
		 * corresponding types in the presence of PAT errata.
		 */
		pat_msr_val = PAT_VALUE(WB, WC, UC_MINUS, UC, WB, WP, UC_MINUS, WT);
	}

	memory_caching_control |= CACHE_PAT;

	init_cache_modes(pat_msr_val);
}

static DEFINE_SPINLOCK(memtype_lock);	/* protects memtype accesses */

/*
 * Does intersection of PAT memory type and MTRR memory type and returns
 * the resulting memory type as PAT understands it.
 * (Type in pat and mtrr will not have same value)
 * The intersection is based on "Effective Memory Type" tables in IA-32
 * SDM vol 3a
 */
static unsigned long pat_x_mtrr_type(u64 start, u64 end,
				     enum page_cache_mode req_type)
{
	/*
	 * Look for MTRR hint to get the effective type in case where PAT
	 * request is for WB.
	 */
	if (req_type == _PAGE_CACHE_MODE_WB) {
		u8 mtrr_type, uniform;

		mtrr_type = mtrr_type_lookup(start, end, &uniform);
		if (mtrr_type != MTRR_TYPE_WRBACK)
			return _PAGE_CACHE_MODE_UC_MINUS;

		return _PAGE_CACHE_MODE_WB;
	}

	return req_type;
}

struct pagerange_state {
	unsigned long		cur_pfn;
	int			ram;
	int			not_ram;
};

static int
pagerange_is_ram_callback(unsigned long initial_pfn, unsigned long total_nr_pages, void *arg)
{
	struct pagerange_state *state = arg;

	state->not_ram	|= initial_pfn > state->cur_pfn;
	state->ram	|= total_nr_pages > 0;
	state->cur_pfn	 = initial_pfn + total_nr_pages;

	return state->ram && state->not_ram;
}

static int pat_pagerange_is_ram(resource_size_t start, resource_size_t end)
{
	int ret = 0;
	unsigned long start_pfn = start >> PAGE_SHIFT;
	unsigned long end_pfn = (end + PAGE_SIZE - 1) >> PAGE_SHIFT;
	struct pagerange_state state = {start_pfn, 0, 0};

	/*
	 * For legacy reasons, physical address range in the legacy ISA
	 * region is tracked as non-RAM. This will allow users of
	 * /dev/mem to map portions of legacy ISA region, even when
	 * some of those portions are listed(or not even listed) with
	 * different e820 types(RAM/reserved/..)
	 */
	if (start_pfn < ISA_END_ADDRESS >> PAGE_SHIFT)
		start_pfn = ISA_END_ADDRESS >> PAGE_SHIFT;

	if (start_pfn < end_pfn) {
		ret = walk_system_ram_range(start_pfn, end_pfn - start_pfn,
				&state, pagerange_is_ram_callback);
	}

	return (ret > 0) ? -1 : (state.ram ? 1 : 0);
}

/*
 * For RAM pages, we use page flags to mark the pages with appropriate type.
 * The page flags are limited to four types, WB (default), WC, WT and UC-.
 * WP request fails with -EINVAL, and UC gets redirected to UC-.  Setting
 * a new memory type is only allowed for a page mapped with the default WB
 * type.
 *
 * Here we do two passes:
 * - Find the memtype of all the pages in the range, look for any conflicts.
 * - In case of no conflicts, set the new memtype for pages in the range.
 */
static int reserve_ram_pages_type(u64 start, u64 end,
				  enum page_cache_mode req_type,
				  enum page_cache_mode *new_type)
{
	struct page *page;
	u64 pfn;

	if (req_type == _PAGE_CACHE_MODE_WP) {
		if (new_type)
			*new_type = _PAGE_CACHE_MODE_UC_MINUS;
		return -EINVAL;
	}

	if (req_type == _PAGE_CACHE_MODE_UC) {
		/* We do not support strong UC */
		WARN_ON_ONCE(1);
		req_type = _PAGE_CACHE_MODE_UC_MINUS;
	}

	for (pfn = (start >> PAGE_SHIFT); pfn < (end >> PAGE_SHIFT); ++pfn) {
		enum page_cache_mode type;

		page = pfn_to_page(pfn);
		type = get_page_memtype(page);
		if (type != _PAGE_CACHE_MODE_WB) {
			pr_info("x86/PAT: reserve_ram_pages_type failed [mem %#010Lx-%#010Lx], track 0x%x, req 0x%x\n",
				start, end - 1, type, req_type);
			if (new_type)
				*new_type = type;

			return -EBUSY;
		}
	}

	if (new_type)
		*new_type = req_type;

	for (pfn = (start >> PAGE_SHIFT); pfn < (end >> PAGE_SHIFT); ++pfn) {
		page = pfn_to_page(pfn);
		set_page_memtype(page, req_type);
	}
	return 0;
}

static int free_ram_pages_type(u64 start, u64 end)
{
	struct page *page;
	u64 pfn;

	for (pfn = (start >> PAGE_SHIFT); pfn < (end >> PAGE_SHIFT); ++pfn) {
		page = pfn_to_page(pfn);
		set_page_memtype(page, _PAGE_CACHE_MODE_WB);
	}
	return 0;
}

static u64 sanitize_phys(u64 address)
{
	/*
	 * When changing the memtype for pages containing poison allow
	 * for a "decoy" virtual address (bit 63 clear) passed to
	 * set_memory_X(). __pa() on a "decoy" address results in a
	 * physical address with bit 63 set.
	 *
	 * Decoy addresses are not present for 32-bit builds, see
	 * set_mce_nospec().
	 */
	if (IS_ENABLED(CONFIG_X86_64))
		return address & __PHYSICAL_MASK;
	return address;
}

/*
 * req_type typically has one of the:
 * - _PAGE_CACHE_MODE_WB
 * - _PAGE_CACHE_MODE_WC
 * - _PAGE_CACHE_MODE_UC_MINUS
 * - _PAGE_CACHE_MODE_UC
 * - _PAGE_CACHE_MODE_WT
 *
 * If new_type is NULL, function will return an error if it cannot reserve the
 * region with req_type. If new_type is non-NULL, function will return
 * available type in new_type in case of no error. In case of any error
 * it will return a negative return value.
 */
int memtype_reserve(u64 start, u64 end, enum page_cache_mode req_type,
		    enum page_cache_mode *new_type)
{
	struct memtype *entry_new;
	enum page_cache_mode actual_type;
	int is_range_ram;
	int err = 0;

	start = sanitize_phys(start);

	/*
	 * The end address passed into this function is exclusive, but
	 * sanitize_phys() expects an inclusive address.
	 */
	end = sanitize_phys(end - 1) + 1;
	if (start >= end) {
		WARN(1, "%s failed: [mem %#010Lx-%#010Lx], req %s\n", __func__,
				start, end - 1, cattr_name(req_type));
		return -EINVAL;
	}

	if (!pat_enabled()) {
		/* This is identical to page table setting without PAT */
		if (new_type)
			*new_type = req_type;
		return 0;
	}

	/* Low ISA region is always mapped WB in page table. No need to track */
	if (x86_platform.is_untracked_pat_range(start, end)) {
		if (new_type)
			*new_type = _PAGE_CACHE_MODE_WB;
		return 0;
	}

	/*
	 * Call mtrr_lookup to get the type hint. This is an
	 * optimization for /dev/mem mmap'ers into WB memory (BIOS
	 * tools and ACPI tools). Use WB request for WB memory and use
	 * UC_MINUS otherwise.
	 */
	actual_type = pat_x_mtrr_type(start, end, req_type);

	if (new_type)
		*new_type = actual_type;

	is_range_ram = pat_pagerange_is_ram(start, end);
	if (is_range_ram == 1) {

		err = reserve_ram_pages_type(start, end, req_type, new_type);

		return err;
	} else if (is_range_ram < 0) {
		return -EINVAL;
	}

	entry_new = kzalloc(sizeof(struct memtype), GFP_KERNEL);
	if (!entry_new)
		return -ENOMEM;

	entry_new->start = start;
	entry_new->end	 = end;
	entry_new->type	 = actual_type;

	spin_lock(&memtype_lock);

	err = memtype_check_insert(entry_new, new_type);
	if (err) {
		pr_info("x86/PAT: memtype_reserve failed [mem %#010Lx-%#010Lx], track %s, req %s\n",
			start, end - 1,
			cattr_name(entry_new->type), cattr_name(req_type));
		kfree(entry_new);
		spin_unlock(&memtype_lock);

		return err;
	}

	spin_unlock(&memtype_lock);

	dprintk("memtype_reserve added [mem %#010Lx-%#010Lx], track %s, req %s, ret %s\n",
		start, end - 1, cattr_name(entry_new->type), cattr_name(req_type),
		new_type ? cattr_name(*new_type) : "-");

	return err;
}

int memtype_free(u64 start, u64 end)
{
	int is_range_ram;
	struct memtype *entry_old;

	if (!pat_enabled())
		return 0;

	start = sanitize_phys(start);
	end = sanitize_phys(end);

	/* Low ISA region is always mapped WB. No need to track */
	if (x86_platform.is_untracked_pat_range(start, end))
		return 0;

	is_range_ram = pat_pagerange_is_ram(start, end);
	if (is_range_ram == 1)
		return free_ram_pages_type(start, end);
	if (is_range_ram < 0)
		return -EINVAL;

	spin_lock(&memtype_lock);
	entry_old = memtype_erase(start, end);
	spin_unlock(&memtype_lock);

	if (IS_ERR(entry_old)) {
		pr_info("x86/PAT: %s:%d freeing invalid memtype [mem %#010Lx-%#010Lx]\n",
			current->comm, current->pid, start, end - 1);
		return -EINVAL;
	}

	kfree(entry_old);

	dprintk("memtype_free request [mem %#010Lx-%#010Lx]\n", start, end - 1);

	return 0;
}


/**
 * lookup_memtype - Looks up the memory type for a physical address
 * @paddr: physical address of which memory type needs to be looked up
 *
 * Only to be called when PAT is enabled
 *
 * Returns _PAGE_CACHE_MODE_WB, _PAGE_CACHE_MODE_WC, _PAGE_CACHE_MODE_UC_MINUS
 * or _PAGE_CACHE_MODE_WT.
 */
static enum page_cache_mode lookup_memtype(u64 paddr)
{
	enum page_cache_mode rettype = _PAGE_CACHE_MODE_WB;
	struct memtype *entry;

	if (x86_platform.is_untracked_pat_range(paddr, paddr + PAGE_SIZE))
		return rettype;

	if (pat_pagerange_is_ram(paddr, paddr + PAGE_SIZE)) {
		struct page *page;

		page = pfn_to_page(paddr >> PAGE_SHIFT);
		return get_page_memtype(page);
	}

	spin_lock(&memtype_lock);

	entry = memtype_lookup(paddr);
	if (entry != NULL)
		rettype = entry->type;
	else
		rettype = _PAGE_CACHE_MODE_UC_MINUS;

	spin_unlock(&memtype_lock);

	return rettype;
}

/**
 * pat_pfn_immune_to_uc_mtrr - Check whether the PAT memory type
 * of @pfn cannot be overridden by UC MTRR memory type.
 * @pfn: The page frame number to check.
 *
 * Only to be called when PAT is enabled.
 *
 * Returns true, if the PAT memory type of @pfn is UC, UC-, or WC.
 * Returns false in other cases.
 */
bool pat_pfn_immune_to_uc_mtrr(unsigned long pfn)
{
	enum page_cache_mode cm = lookup_memtype(PFN_PHYS(pfn));

	return cm == _PAGE_CACHE_MODE_UC ||
	       cm == _PAGE_CACHE_MODE_UC_MINUS ||
	       cm == _PAGE_CACHE_MODE_WC;
}
EXPORT_SYMBOL_GPL(pat_pfn_immune_to_uc_mtrr);

/**
 * memtype_reserve_io - Request a memory type mapping for a region of memory
 * @start: start (physical address) of the region
 * @end: end (physical address) of the region
 * @type: A pointer to memtype, with requested type. On success, requested
 * or any other compatible type that was available for the region is returned
 *
 * On success, returns 0
 * On failure, returns non-zero
 */
int memtype_reserve_io(resource_size_t start, resource_size_t end,
			enum page_cache_mode *type)
{
	resource_size_t size = end - start;
	enum page_cache_mode req_type = *type;
	enum page_cache_mode new_type;
	int ret;

	WARN_ON_ONCE(iomem_map_sanity_check(start, size));

	ret = memtype_reserve(start, end, req_type, &new_type);
	if (ret)
		goto out_err;

	if (!is_new_memtype_allowed(start, size, req_type, new_type))
		goto out_free;

	if (memtype_kernel_map_sync(start, size, new_type) < 0)
		goto out_free;

	*type = new_type;
	return 0;

out_free:
	memtype_free(start, end);
	ret = -EBUSY;
out_err:
	return ret;
}

/**
 * memtype_free_io - Release a memory type mapping for a region of memory
 * @start: start (physical address) of the region
 * @end: end (physical address) of the region
 */
void memtype_free_io(resource_size_t start, resource_size_t end)
{
	memtype_free(start, end);
}

#ifdef CONFIG_X86_PAT
int arch_io_reserve_memtype_wc(resource_size_t start, resource_size_t size)
{
	enum page_cache_mode type = _PAGE_CACHE_MODE_WC;

	return memtype_reserve_io(start, start + size, &type);
}
EXPORT_SYMBOL(arch_io_reserve_memtype_wc);

void arch_io_free_memtype_wc(resource_size_t start, resource_size_t size)
{
	memtype_free_io(start, start + size);
}
EXPORT_SYMBOL(arch_io_free_memtype_wc);
#endif

pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
				unsigned long size, pgprot_t vma_prot)
{
	if (!phys_mem_access_encrypted(pfn << PAGE_SHIFT, size))
		vma_prot = pgprot_decrypted(vma_prot);

	return vma_prot;
}

static inline void pgprot_set_cachemode(pgprot_t *prot, enum page_cache_mode pcm)
{
	*prot = __pgprot((pgprot_val(*prot) & ~_PAGE_CACHE_MASK) |
			 cachemode2protval(pcm));
}

int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
				unsigned long size, pgprot_t *vma_prot)
{
	enum page_cache_mode pcm = _PAGE_CACHE_MODE_WB;

	if (!pat_enabled())
		return 1;

	if (!range_is_allowed(pfn, size))
		return 0;

	if (file->f_flags & O_DSYNC)
		pcm = _PAGE_CACHE_MODE_UC_MINUS;

	pgprot_set_cachemode(vma_prot, pcm);
	return 1;
}

/*
 * Change the memory type for the physical address range in kernel identity
 * mapping space if that range is a part of identity map.
 */
int memtype_kernel_map_sync(u64 base, unsigned long size,
			    enum page_cache_mode pcm)
{
	unsigned long id_sz;

	if (base > __pa(high_memory-1))
		return 0;

	/*
	 * Some areas in the middle of the kernel identity range
	 * are not mapped, for example the PCI space.
	 */
	if (!page_is_ram(base >> PAGE_SHIFT))
		return 0;

	id_sz = (__pa(high_memory-1) <= base + size) ?
				__pa(high_memory) - base : size;

	if (ioremap_change_attr((unsigned long)__va(base), id_sz, pcm) < 0) {
		pr_info("x86/PAT: %s:%d ioremap_change_attr failed %s for [mem %#010Lx-%#010Lx]\n",
			current->comm, current->pid,
			cattr_name(pcm),
			base, (unsigned long long)(base + size-1));
		return -EINVAL;
	}
	return 0;
}

/*
 * Internal interface to reserve a range of physical memory with prot.
 * Reserved non RAM regions only and after successful memtype_reserve,
 * this func also keeps identity mapping (if any) in sync with this new prot.
 */
static int reserve_pfn_range(u64 paddr, unsigned long size, pgprot_t *vma_prot)
{
	int is_ram = 0;
	int ret;
	enum page_cache_mode want_pcm = pgprot2cachemode(*vma_prot);
	enum page_cache_mode pcm = want_pcm;

	is_ram = pat_pagerange_is_ram(paddr, paddr + size);

	/*
	 * reserve_pfn_range() for RAM pages. We do not refcount to keep
	 * track of number of mappings of RAM pages. We can assert that
	 * the type requested matches the type of first page in the range.
	 */
	if (is_ram) {
		if (!pat_enabled())
			return 0;

		pcm = lookup_memtype(paddr);
		if (want_pcm != pcm) {
			pr_warn("x86/PAT: %s:%d map pfn RAM range req %s for [mem %#010Lx-%#010Lx], got %s\n",
				current->comm, current->pid,
				cattr_name(want_pcm),
				(unsigned long long)paddr,
				(unsigned long long)(paddr + size - 1),
				cattr_name(pcm));
			pgprot_set_cachemode(vma_prot, pcm);
		}
		return 0;
	}

	ret = memtype_reserve(paddr, paddr + size, want_pcm, &pcm);
	if (ret)
		return ret;

	if (pcm != want_pcm) {
		if (!is_new_memtype_allowed(paddr, size, want_pcm, pcm)) {
			memtype_free(paddr, paddr + size);
			pr_err("x86/PAT: %s:%d map pfn expected mapping type %s for [mem %#010Lx-%#010Lx], got %s\n",
			       current->comm, current->pid,
			       cattr_name(want_pcm),
			       (unsigned long long)paddr,
			       (unsigned long long)(paddr + size - 1),
			       cattr_name(pcm));
			return -EINVAL;
		}
		pgprot_set_cachemode(vma_prot, pcm);
	}

	if (memtype_kernel_map_sync(paddr, size, pcm) < 0) {
		memtype_free(paddr, paddr + size);
		return -EINVAL;
	}
	return 0;
}

/*
 * Internal interface to free a range of physical memory.
 * Frees non RAM regions only.
 */
static void free_pfn_range(u64 paddr, unsigned long size)
{
	int is_ram;

	is_ram = pat_pagerange_is_ram(paddr, paddr + size);
	if (is_ram == 0)
		memtype_free(paddr, paddr + size);
}

int pfnmap_setup_cachemode(unsigned long pfn, unsigned long size, pgprot_t *prot)
{
	resource_size_t paddr = (resource_size_t)pfn << PAGE_SHIFT;
	enum page_cache_mode pcm;

	if (!pat_enabled())
		return 0;

	pcm = lookup_memtype(paddr);

	/* Check memtype for the remaining pages */
	while (size > PAGE_SIZE) {
		size -= PAGE_SIZE;
		paddr += PAGE_SIZE;
		if (pcm != lookup_memtype(paddr))
			return -EINVAL;
	}

	pgprot_set_cachemode(prot, pcm);
	return 0;
}

int pfnmap_track(unsigned long pfn, unsigned long size, pgprot_t *prot)
{
	const resource_size_t paddr = (resource_size_t)pfn << PAGE_SHIFT;

	return reserve_pfn_range(paddr, size, prot);
}

void pfnmap_untrack(unsigned long pfn, unsigned long size)
{
	const resource_size_t paddr = (resource_size_t)pfn << PAGE_SHIFT;

	free_pfn_range(paddr, size);
}

pgprot_t pgprot_writecombine(pgprot_t prot)
{
	pgprot_set_cachemode(&prot, _PAGE_CACHE_MODE_WC);
	return prot;
}
EXPORT_SYMBOL_GPL(pgprot_writecombine);

pgprot_t pgprot_writethrough(pgprot_t prot)
{
	pgprot_set_cachemode(&prot, _PAGE_CACHE_MODE_WT);
	return prot;
}
EXPORT_SYMBOL_GPL(pgprot_writethrough);

#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_X86_PAT)

/*
 * We are allocating a temporary printout-entry to be passed
 * between seq_start()/next() and seq_show():
 */
static struct memtype *memtype_get_idx(loff_t pos)
{
	struct memtype *entry_print;
	int ret;

	entry_print  = kzalloc(sizeof(struct memtype), GFP_KERNEL);
	if (!entry_print)
		return NULL;

	spin_lock(&memtype_lock);
	ret = memtype_copy_nth_element(entry_print, pos);
	spin_unlock(&memtype_lock);

	/* Free it on error: */
	if (ret) {
		kfree(entry_print);
		return NULL;
	}

	return entry_print;
}

static void *memtype_seq_start(struct seq_file *seq, loff_t *pos)
{
	if (*pos == 0) {
		++*pos;
		seq_puts(seq, "PAT memtype list:\n");
	}

	return memtype_get_idx(*pos);
}

static void *memtype_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
	kfree(v);
	++*pos;
	return memtype_get_idx(*pos);
}

static void memtype_seq_stop(struct seq_file *seq, void *v)
{
	kfree(v);
}

static int memtype_seq_show(struct seq_file *seq, void *v)
{
	struct memtype *entry_print = (struct memtype *)v;

	seq_printf(seq, "PAT: [mem 0x%016Lx-0x%016Lx] %s\n",
			entry_print->start,
			entry_print->end,
			cattr_name(entry_print->type));

	return 0;
}

static const struct seq_operations memtype_seq_ops = {
	.start = memtype_seq_start,
	.next  = memtype_seq_next,
	.stop  = memtype_seq_stop,
	.show  = memtype_seq_show,
};

static int memtype_seq_open(struct inode *inode, struct file *file)
{
	return seq_open(file, &memtype_seq_ops);
}

static const struct file_operations memtype_fops = {
	.open    = memtype_seq_open,
	.read    = seq_read,
	.llseek  = seq_lseek,
	.release = seq_release,
};

static int __init pat_memtype_list_init(void)
{
	if (pat_enabled()) {
		debugfs_create_file("pat_memtype_list", S_IRUSR,
				    arch_debugfs_dir, NULL, &memtype_fops);
	}
	return 0;
}
late_initcall(pat_memtype_list_init);

#endif /* CONFIG_DEBUG_FS && CONFIG_X86_PAT */