arch/powerpc/mm/init_64.c - third_party/linux - Git at Google

 /*
  *  PowerPC version
  *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
  *
  *  Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
  *  and Cort Dougan (PReP) (cort@cs.nmt.edu)
  *    Copyright (C) 1996 Paul Mackerras
  *
  *  Derived from "arch/i386/mm/init.c"
  *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  *
  *  Dave Engebretsen <engebret@us.ibm.com>
  *      Rework for PPC64 port.
  *
  *  This program is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU General Public License
  *  as published by the Free Software Foundation; either version
  *  2 of the License, or (at your option) any later version.
  *
  */

 #undef DEBUG

 #include <linux/signal.h>
 #include <linux/sched.h>
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/mman.h>
 #include <linux/mm.h>
 #include <linux/swap.h>
 #include <linux/stddef.h>
 #include <linux/vmalloc.h>
 #include <linux/init.h>
 #include <linux/delay.h>
 #include <linux/highmem.h>
 #include <linux/idr.h>
 #include <linux/nodemask.h>
 #include <linux/module.h>
 #include <linux/poison.h>
 #include <linux/memblock.h>
 #include <linux/hugetlb.h>
 #include <linux/slab.h>
 #include <linux/of_fdt.h>
 #include <linux/libfdt.h>
 #include <linux/memremap.h>

 #include <asm/pgalloc.h>
 #include <asm/page.h>
 #include <asm/prom.h>
 #include <asm/rtas.h>
 #include <asm/io.h>
 #include <asm/mmu_context.h>
 #include <asm/pgtable.h>
 #include <asm/mmu.h>
 #include <linux/uaccess.h>
 #include <asm/smp.h>
 #include <asm/machdep.h>
 #include <asm/tlb.h>
 #include <asm/eeh.h>
 #include <asm/processor.h>
 #include <asm/mmzone.h>
 #include <asm/cputable.h>
 #include <asm/sections.h>
 #include <asm/iommu.h>
 #include <asm/vdso.h>

 #include "mmu_decl.h"

 phys_addr_t memstart_addr = ~0;
 EXPORT_SYMBOL_GPL(memstart_addr);
 phys_addr_t kernstart_addr;
 EXPORT_SYMBOL_GPL(kernstart_addr);

 #ifdef CONFIG_SPARSEMEM_VMEMMAP
 /*
  * Given an address within the vmemmap, determine the pfn of the page that
  * represents the start of the section it is within.  Note that we have to
  * do this by hand as the proffered address may not be correctly aligned.
  * Subtraction of non-aligned pointers produces undefined results.
  */
 static unsigned long __meminit vmemmap_section_start(unsigned long page)
 {
 	unsigned long offset = page - ((unsigned long)(vmemmap));

 	/* Return the pfn of the start of the section. */
 	return (offset / sizeof(struct page)) & PAGE_SECTION_MASK;
 }

 /*
  * Check if this vmemmap page is already initialised.  If any section
  * which overlaps this vmemmap page is initialised then this page is
  * initialised already.
  */
 static int __meminit vmemmap_populated(unsigned long start, int page_size)
 {
 	unsigned long end = start + page_size;
 	start = (unsigned long)(pfn_to_page(vmemmap_section_start(start)));

 	for (; start < end; start += (PAGES_PER_SECTION * sizeof(struct page)))
 		if (pfn_valid(page_to_pfn((struct page *)start)))
 			return 1;

 	return 0;
 }

 /*
  * vmemmap virtual address space management does not have a traditonal page
  * table to track which virtual struct pages are backed by physical mapping.
  * The virtual to physical mappings are tracked in a simple linked list
  * format. 'vmemmap_list' maintains the entire vmemmap physical mapping at
  * all times where as the 'next' list maintains the available
  * vmemmap_backing structures which have been deleted from the
  * 'vmemmap_global' list during system runtime (memory hotplug remove
  * operation). The freed 'vmemmap_backing' structures are reused later when
  * new requests come in without allocating fresh memory. This pointer also
  * tracks the allocated 'vmemmap_backing' structures as we allocate one
  * full page memory at a time when we dont have any.
  */
 struct vmemmap_backing *vmemmap_list;
 static struct vmemmap_backing *next;

 /*
  * The same pointer 'next' tracks individual chunks inside the allocated
  * full page during the boot time and again tracks the freeed nodes during
  * runtime. It is racy but it does not happen as they are separated by the
  * boot process. Will create problem if some how we have memory hotplug
  * operation during boot !!
  */
 static int num_left;
 static int num_freed;

 static __meminit struct vmemmap_backing * vmemmap_list_alloc(int node)
 {
 	struct vmemmap_backing *vmem_back;
 	/* get from freed entries first */
 	if (num_freed) {
 		num_freed--;
 		vmem_back = next;
 		next = next->list;

 		return vmem_back;
 	}

 	/* allocate a page when required and hand out chunks */
 	if (!num_left) {
 		next = vmemmap_alloc_block(PAGE_SIZE, node);
 		if (unlikely(!next)) {
 			WARN_ON(1);
 			return NULL;
 		}
 		num_left = PAGE_SIZE / sizeof(struct vmemmap_backing);
 	}

 	num_left--;

 	return next++;
 }

 static __meminit void vmemmap_list_populate(unsigned long phys,
 					    unsigned long start,
 					    int node)
 {
 	struct vmemmap_backing *vmem_back;

 	vmem_back = vmemmap_list_alloc(node);
 	if (unlikely(!vmem_back)) {
 		WARN_ON(1);
 		return;
 	}

 	vmem_back->phys = phys;
 	vmem_back->virt_addr = start;
 	vmem_back->list = vmemmap_list;

 	vmemmap_list = vmem_back;
 }

 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 		struct vmem_altmap *altmap)
 {
 	unsigned long page_size = 1 << mmu_psize_defs[mmu_vmemmap_psize].shift;

 	/* Align to the page size of the linear mapping. */
 	start = _ALIGN_DOWN(start, page_size);

 	pr_debug("vmemmap_populate %lx..%lx, node %d\n", start, end, node);

 	for (; start < end; start += page_size) {
 		void *p;
 		int rc;

 		if (vmemmap_populated(start, page_size))
 			continue;

 		if (altmap)
 			p = altmap_alloc_block_buf(page_size, altmap);
 		else
 			p = vmemmap_alloc_block_buf(page_size, node);
 		if (!p)
 			return -ENOMEM;

 		vmemmap_list_populate(__pa(p), start, node);

 		pr_debug("      * %016lx..%016lx allocated at %p\n",
 			 start, start + page_size, p);

 		rc = vmemmap_create_mapping(start, page_size, __pa(p));
 		if (rc < 0) {
 			pr_warn("%s: Unable to create vmemmap mapping: %d\n",
 				__func__, rc);
 			return -EFAULT;
 		}
 	}

 	return 0;
 }

 #ifdef CONFIG_MEMORY_HOTPLUG
 static unsigned long vmemmap_list_free(unsigned long start)
 {
 	struct vmemmap_backing *vmem_back, *vmem_back_prev;

 	vmem_back_prev = vmem_back = vmemmap_list;

 	/* look for it with prev pointer recorded */
 	for (; vmem_back; vmem_back = vmem_back->list) {
 		if (vmem_back->virt_addr == start)
 			break;
 		vmem_back_prev = vmem_back;
 	}

 	if (unlikely(!vmem_back)) {
 		WARN_ON(1);
 		return 0;
 	}

 	/* remove it from vmemmap_list */
 	if (vmem_back == vmemmap_list) /* remove head */
 		vmemmap_list = vmem_back->list;
 	else
 		vmem_back_prev->list = vmem_back->list;

 	/* next point to this freed entry */
 	vmem_back->list = next;
 	next = vmem_back;
 	num_freed++;

 	return vmem_back->phys;
 }

 void __ref vmemmap_free(unsigned long start, unsigned long end,
 		struct vmem_altmap *altmap)
 {
 	unsigned long page_size = 1 << mmu_psize_defs[mmu_vmemmap_psize].shift;
 	unsigned long page_order = get_order(page_size);

 	start = _ALIGN_DOWN(start, page_size);

 	pr_debug("vmemmap_free %lx...%lx\n", start, end);

 	for (; start < end; start += page_size) {
 		unsigned long nr_pages, addr;
 		struct page *section_base;
 		struct page *page;

 		/*
 		 * the section has already be marked as invalid, so
 		 * vmemmap_populated() true means some other sections still
 		 * in this page, so skip it.
 		 */
 		if (vmemmap_populated(start, page_size))
 			continue;

 		addr = vmemmap_list_free(start);
 		if (!addr)
 			continue;

 		page = pfn_to_page(addr >> PAGE_SHIFT);
 		section_base = pfn_to_page(vmemmap_section_start(start));
 		nr_pages = 1 << page_order;

 		if (altmap) {
 			vmem_altmap_free(altmap, nr_pages);
 		} else if (PageReserved(page)) {
 			/* allocated from bootmem */
 			if (page_size < PAGE_SIZE) {
 				/*
 				 * this shouldn't happen, but if it is
 				 * the case, leave the memory there
 				 */
 				WARN_ON_ONCE(1);
 			} else {
 				while (nr_pages--)
 					free_reserved_page(page++);
 			}
 		} else {
 			free_pages((unsigned long)(__va(addr)), page_order);
 		}

 		vmemmap_remove_mapping(start, page_size);
 	}
 }
 #endif
 void register_page_bootmem_memmap(unsigned long section_nr,
 				  struct page *start_page, unsigned long size)
 {
 }

 /*
  * We do not have access to the sparsemem vmemmap, so we fallback to
  * walking the list of sparsemem blocks which we already maintain for
  * the sake of crashdump. In the long run, we might want to maintain
  * a tree if performance of that linear walk becomes a problem.
  *
  * realmode_pfn_to_page functions can fail due to:
  * 1) As real sparsemem blocks do not lay in RAM continously (they
  * are in virtual address space which is not available in the real mode),
  * the requested page struct can be split between blocks so get_page/put_page
  * may fail.
  * 2) When huge pages are used, the get_page/put_page API will fail
  * in real mode as the linked addresses in the page struct are virtual
  * too.
  */
 struct page *realmode_pfn_to_page(unsigned long pfn)
 {
 	struct vmemmap_backing *vmem_back;
 	struct page *page;
 	unsigned long page_size = 1 << mmu_psize_defs[mmu_vmemmap_psize].shift;
 	unsigned long pg_va = (unsigned long) pfn_to_page(pfn);

 	for (vmem_back = vmemmap_list; vmem_back; vmem_back = vmem_back->list) {
 		if (pg_va < vmem_back->virt_addr)
 			continue;

 		/* After vmemmap_list entry free is possible, need check all */
 		if ((pg_va + sizeof(struct page)) <=
 				(vmem_back->virt_addr + page_size)) {
 			page = (struct page *) (vmem_back->phys + pg_va -
 				vmem_back->virt_addr);
 			return page;
 		}
 	}

 	/* Probably that page struct is split between real pages */
 	return NULL;
 }
 EXPORT_SYMBOL_GPL(realmode_pfn_to_page);

 #else

 struct page *realmode_pfn_to_page(unsigned long pfn)
 {
 	struct page *page = pfn_to_page(pfn);
 	return page;
 }
 EXPORT_SYMBOL_GPL(realmode_pfn_to_page);

 #endif /* CONFIG_SPARSEMEM_VMEMMAP */

 #ifdef CONFIG_PPC_BOOK3S_64
 static bool disable_radix = !IS_ENABLED(CONFIG_PPC_RADIX_MMU_DEFAULT);

 static int __init parse_disable_radix(char *p)
 {
 	bool val;

 	if (!p)
 		val = true;
 	else if (kstrtobool(p, &val))
 		return -EINVAL;

 	disable_radix = val;

 	return 0;
 }
 early_param("disable_radix", parse_disable_radix);

 /*
  * If we're running under a hypervisor, we need to check the contents of
  * /chosen/ibm,architecture-vec-5 to see if the hypervisor is willing to do
  * radix.  If not, we clear the radix feature bit so we fall back to hash.
  */
 static void __init early_check_vec5(void)
 {
 	unsigned long root, chosen;
 	int size;
 	const u8 *vec5;
 	u8 mmu_supported;

 	root = of_get_flat_dt_root();
 	chosen = of_get_flat_dt_subnode_by_name(root, "chosen");
 	if (chosen == -FDT_ERR_NOTFOUND) {
 		cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
 		return;
 	}
 	vec5 = of_get_flat_dt_prop(chosen, "ibm,architecture-vec-5", &size);
 	if (!vec5) {
 		cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
 		return;
 	}
 	if (size <= OV5_INDX(OV5_MMU_SUPPORT)) {
 		cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
 		return;
 	}

 	/* Check for supported configuration */
 	mmu_supported = vec5[OV5_INDX(OV5_MMU_SUPPORT)] &
 			OV5_FEAT(OV5_MMU_SUPPORT);
 	if (mmu_supported == OV5_FEAT(OV5_MMU_RADIX)) {
 		/* Hypervisor only supports radix - check enabled && GTSE */
 		if (!early_radix_enabled()) {
 			pr_warn("WARNING: Ignoring cmdline option disable_radix\n");
 		}
 		if (!(vec5[OV5_INDX(OV5_RADIX_GTSE)] &
 						OV5_FEAT(OV5_RADIX_GTSE))) {
 			pr_warn("WARNING: Hypervisor doesn't support RADIX with GTSE\n");
 		}
 		/* Do radix anyway - the hypervisor said we had to */
 		cur_cpu_spec->mmu_features |= MMU_FTR_TYPE_RADIX;
 	} else if (mmu_supported == OV5_FEAT(OV5_MMU_HASH)) {
 		/* Hypervisor only supports hash - disable radix */
 		cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
 	}
 }

 void __init mmu_early_init_devtree(void)
 {
 	/* Disable radix mode based on kernel command line. */
 	if (disable_radix)
 		cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;

 	/*
 	 * Check /chosen/ibm,architecture-vec-5 if running as a guest.
 	 * When running bare-metal, we can use radix if we like
 	 * even though the ibm,architecture-vec-5 property created by
 	 * skiboot doesn't have the necessary bits set.
 	 */
 	if (!(mfmsr() & MSR_HV))
 		early_check_vec5();

 	if (early_radix_enabled())
 		radix__early_init_devtree();
 	else
 		hash__early_init_devtree();
 }
 #endif /* CONFIG_PPC_BOOK3S_64 */
	/*
	* PowerPC version
	* Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
	*
	* Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
	* and Cort Dougan (PReP) (cort@cs.nmt.edu)
	* Copyright (C) 1996 Paul Mackerras
	*
	* Derived from "arch/i386/mm/init.c"
	* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
	*
	* Dave Engebretsen <engebret@us.ibm.com>
	* Rework for PPC64 port.
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License
	* as published by the Free Software Foundation; either version
	* 2 of the License, or (at your option) any later version.
	*
	*/

	#undef DEBUG

	#include <linux/signal.h>
	#include <linux/sched.h>
	#include <linux/kernel.h>
	#include <linux/errno.h>
	#include <linux/string.h>
	#include <linux/types.h>
	#include <linux/mman.h>
	#include <linux/mm.h>
	#include <linux/swap.h>
	#include <linux/stddef.h>
	#include <linux/vmalloc.h>
	#include <linux/init.h>
	#include <linux/delay.h>
	#include <linux/highmem.h>
	#include <linux/idr.h>
	#include <linux/nodemask.h>
	#include <linux/module.h>
	#include <linux/poison.h>
	#include <linux/memblock.h>
	#include <linux/hugetlb.h>
	#include <linux/slab.h>
	#include <linux/of_fdt.h>
	#include <linux/libfdt.h>
	#include <linux/memremap.h>

	#include <asm/pgalloc.h>
	#include <asm/page.h>
	#include <asm/prom.h>
	#include <asm/rtas.h>
	#include <asm/io.h>
	#include <asm/mmu_context.h>
	#include <asm/pgtable.h>
	#include <asm/mmu.h>
	#include <linux/uaccess.h>
	#include <asm/smp.h>
	#include <asm/machdep.h>
	#include <asm/tlb.h>
	#include <asm/eeh.h>
	#include <asm/processor.h>
	#include <asm/mmzone.h>
	#include <asm/cputable.h>
	#include <asm/sections.h>
	#include <asm/iommu.h>
	#include <asm/vdso.h>

	#include "mmu_decl.h"

	phys_addr_t memstart_addr = ~0;
	EXPORT_SYMBOL_GPL(memstart_addr);
	phys_addr_t kernstart_addr;
	EXPORT_SYMBOL_GPL(kernstart_addr);

	#ifdef CONFIG_SPARSEMEM_VMEMMAP
	/*
	* Given an address within the vmemmap, determine the pfn of the page that
	* represents the start of the section it is within. Note that we have to
	* do this by hand as the proffered address may not be correctly aligned.
	* Subtraction of non-aligned pointers produces undefined results.
	*/
	static unsigned long __meminit vmemmap_section_start(unsigned long page)
	{
	unsigned long offset = page - ((unsigned long)(vmemmap));

	/* Return the pfn of the start of the section. */
	return (offset / sizeof(struct page)) & PAGE_SECTION_MASK;
	}

	/*
	* Check if this vmemmap page is already initialised. If any section
	* which overlaps this vmemmap page is initialised then this page is
	* initialised already.
	*/
	static int __meminit vmemmap_populated(unsigned long start, int page_size)
	{
	unsigned long end = start + page_size;
	start = (unsigned long)(pfn_to_page(vmemmap_section_start(start)));

	for (; start < end; start += (PAGES_PER_SECTION * sizeof(struct page)))
	if (pfn_valid(page_to_pfn((struct page *)start)))
	return 1;

	return 0;
	}

	/*
	* vmemmap virtual address space management does not have a traditonal page
	* table to track which virtual struct pages are backed by physical mapping.
	* The virtual to physical mappings are tracked in a simple linked list
	* format. 'vmemmap_list' maintains the entire vmemmap physical mapping at
	* all times where as the 'next' list maintains the available
	* vmemmap_backing structures which have been deleted from the
	* 'vmemmap_global' list during system runtime (memory hotplug remove
	* operation). The freed 'vmemmap_backing' structures are reused later when
	* new requests come in without allocating fresh memory. This pointer also
	* tracks the allocated 'vmemmap_backing' structures as we allocate one
	* full page memory at a time when we dont have any.
	*/
	struct vmemmap_backing *vmemmap_list;
	static struct vmemmap_backing *next;

	/*
	* The same pointer 'next' tracks individual chunks inside the allocated
	* full page during the boot time and again tracks the freeed nodes during
	* runtime. It is racy but it does not happen as they are separated by the
	* boot process. Will create problem if some how we have memory hotplug
	* operation during boot !!
	*/
	static int num_left;
	static int num_freed;

	static __meminit struct vmemmap_backing * vmemmap_list_alloc(int node)
	{
	struct vmemmap_backing *vmem_back;
	/* get from freed entries first */
	if (num_freed) {
	num_freed--;
	vmem_back = next;
	next = next->list;

	return vmem_back;
	}

	/* allocate a page when required and hand out chunks */
	if (!num_left) {
	next = vmemmap_alloc_block(PAGE_SIZE, node);
	if (unlikely(!next)) {
	WARN_ON(1);
	return NULL;
	}
	num_left = PAGE_SIZE / sizeof(struct vmemmap_backing);
	}

	num_left--;

	return next++;
	}

	static __meminit void vmemmap_list_populate(unsigned long phys,
	unsigned long start,
	int node)
	{
	struct vmemmap_backing *vmem_back;

	vmem_back = vmemmap_list_alloc(node);
	if (unlikely(!vmem_back)) {
	WARN_ON(1);
	return;
	}

	vmem_back->phys = phys;
	vmem_back->virt_addr = start;
	vmem_back->list = vmemmap_list;

	vmemmap_list = vmem_back;
	}

	int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
	struct vmem_altmap *altmap)
	{
	unsigned long page_size = 1 << mmu_psize_defs[mmu_vmemmap_psize].shift;

	/* Align to the page size of the linear mapping. */
	start = _ALIGN_DOWN(start, page_size);

	pr_debug("vmemmap_populate %lx..%lx, node %d\n", start, end, node);

	for (; start < end; start += page_size) {
	void *p;
	int rc;

	if (vmemmap_populated(start, page_size))
	continue;

	if (altmap)
	p = altmap_alloc_block_buf(page_size, altmap);
	else
	p = vmemmap_alloc_block_buf(page_size, node);
	if (!p)
	return -ENOMEM;

	vmemmap_list_populate(__pa(p), start, node);

	pr_debug(" * %016lx..%016lx allocated at %p\n",
	start, start + page_size, p);

	rc = vmemmap_create_mapping(start, page_size, __pa(p));
	if (rc < 0) {
	pr_warn("%s: Unable to create vmemmap mapping: %d\n",
	__func__, rc);
	return -EFAULT;
	}
	}

	return 0;
	}

	#ifdef CONFIG_MEMORY_HOTPLUG
	static unsigned long vmemmap_list_free(unsigned long start)
	{
	struct vmemmap_backing vmem_back, vmem_back_prev;

	vmem_back_prev = vmem_back = vmemmap_list;

	/* look for it with prev pointer recorded */
	for (; vmem_back; vmem_back = vmem_back->list) {
	if (vmem_back->virt_addr == start)
	break;
	vmem_back_prev = vmem_back;
	}

	if (unlikely(!vmem_back)) {
	WARN_ON(1);
	return 0;
	}

	/* remove it from vmemmap_list */
	if (vmem_back == vmemmap_list) /* remove head */
	vmemmap_list = vmem_back->list;
	else
	vmem_back_prev->list = vmem_back->list;

	/* next point to this freed entry */
	vmem_back->list = next;
	next = vmem_back;
	num_freed++;

	return vmem_back->phys;
	}

	void __ref vmemmap_free(unsigned long start, unsigned long end,
	struct vmem_altmap *altmap)
	{
	unsigned long page_size = 1 << mmu_psize_defs[mmu_vmemmap_psize].shift;
	unsigned long page_order = get_order(page_size);

	start = _ALIGN_DOWN(start, page_size);

	pr_debug("vmemmap_free %lx...%lx\n", start, end);

	for (; start < end; start += page_size) {
	unsigned long nr_pages, addr;
	struct page *section_base;
	struct page *page;

	/*
	* the section has already be marked as invalid, so
	* vmemmap_populated() true means some other sections still
	* in this page, so skip it.
	*/
	if (vmemmap_populated(start, page_size))
	continue;

	addr = vmemmap_list_free(start);
	if (!addr)
	continue;

	page = pfn_to_page(addr >> PAGE_SHIFT);
	section_base = pfn_to_page(vmemmap_section_start(start));
	nr_pages = 1 << page_order;

	if (altmap) {
	vmem_altmap_free(altmap, nr_pages);
	} else if (PageReserved(page)) {
	/* allocated from bootmem */
	if (page_size < PAGE_SIZE) {
	/*
	* this shouldn't happen, but if it is
	* the case, leave the memory there
	*/
	WARN_ON_ONCE(1);
	} else {
	while (nr_pages--)
	free_reserved_page(page++);
	}
	} else {
	free_pages((unsigned long)(__va(addr)), page_order);
	}

	vmemmap_remove_mapping(start, page_size);
	}
	}
	#endif
	void register_page_bootmem_memmap(unsigned long section_nr,
	struct page *start_page, unsigned long size)
	{
	}

	/*
	* We do not have access to the sparsemem vmemmap, so we fallback to
	* walking the list of sparsemem blocks which we already maintain for
	* the sake of crashdump. In the long run, we might want to maintain
	* a tree if performance of that linear walk becomes a problem.
	*
	* realmode_pfn_to_page functions can fail due to:
	* 1) As real sparsemem blocks do not lay in RAM continously (they
	* are in virtual address space which is not available in the real mode),
	* the requested page struct can be split between blocks so get_page/put_page
	* may fail.
	* 2) When huge pages are used, the get_page/put_page API will fail
	* in real mode as the linked addresses in the page struct are virtual
	* too.
	*/
	struct page *realmode_pfn_to_page(unsigned long pfn)
	{
	struct vmemmap_backing *vmem_back;
	struct page *page;
	unsigned long page_size = 1 << mmu_psize_defs[mmu_vmemmap_psize].shift;
	unsigned long pg_va = (unsigned long) pfn_to_page(pfn);

	for (vmem_back = vmemmap_list; vmem_back; vmem_back = vmem_back->list) {
	if (pg_va < vmem_back->virt_addr)
	continue;

	/* After vmemmap_list entry free is possible, need check all */
	if ((pg_va + sizeof(struct page)) <=
	(vmem_back->virt_addr + page_size)) {
	page = (struct page *) (vmem_back->phys + pg_va -
	vmem_back->virt_addr);
	return page;
	}
	}

	/* Probably that page struct is split between real pages */
	return NULL;
	}
	EXPORT_SYMBOL_GPL(realmode_pfn_to_page);

	#else

	struct page *realmode_pfn_to_page(unsigned long pfn)
	{
	struct page *page = pfn_to_page(pfn);
	return page;
	}
	EXPORT_SYMBOL_GPL(realmode_pfn_to_page);

	#endif /* CONFIG_SPARSEMEM_VMEMMAP */

	#ifdef CONFIG_PPC_BOOK3S_64
	static bool disable_radix = !IS_ENABLED(CONFIG_PPC_RADIX_MMU_DEFAULT);

	static int __init parse_disable_radix(char *p)
	{
	bool val;

	if (!p)
	val = true;
	else if (kstrtobool(p, &val))
	return -EINVAL;

	disable_radix = val;

	return 0;
	}
	early_param("disable_radix", parse_disable_radix);

	/*
	* If we're running under a hypervisor, we need to check the contents of
	* /chosen/ibm,architecture-vec-5 to see if the hypervisor is willing to do
	* radix. If not, we clear the radix feature bit so we fall back to hash.
	*/
	static void __init early_check_vec5(void)
	{
	unsigned long root, chosen;
	int size;
	const u8 *vec5;
	u8 mmu_supported;

	root = of_get_flat_dt_root();
	chosen = of_get_flat_dt_subnode_by_name(root, "chosen");
	if (chosen == -FDT_ERR_NOTFOUND) {
	cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
	return;
	}
	vec5 = of_get_flat_dt_prop(chosen, "ibm,architecture-vec-5", &size);
	if (!vec5) {
	cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
	return;
	}
	if (size <= OV5_INDX(OV5_MMU_SUPPORT)) {
	cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
	return;
	}

	/* Check for supported configuration */
	mmu_supported = vec5[OV5_INDX(OV5_MMU_SUPPORT)] &
	OV5_FEAT(OV5_MMU_SUPPORT);
	if (mmu_supported == OV5_FEAT(OV5_MMU_RADIX)) {
	/* Hypervisor only supports radix - check enabled && GTSE */
	if (!early_radix_enabled()) {
	pr_warn("WARNING: Ignoring cmdline option disable_radix\n");
	}
	if (!(vec5[OV5_INDX(OV5_RADIX_GTSE)] &
	OV5_FEAT(OV5_RADIX_GTSE))) {
	pr_warn("WARNING: Hypervisor doesn't support RADIX with GTSE\n");
	}
	/* Do radix anyway - the hypervisor said we had to */
	cur_cpu_spec->mmu_features \|= MMU_FTR_TYPE_RADIX;
	} else if (mmu_supported == OV5_FEAT(OV5_MMU_HASH)) {
	/* Hypervisor only supports hash - disable radix */
	cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
	}
	}

	void __init mmu_early_init_devtree(void)
	{
	/* Disable radix mode based on kernel command line. */
	if (disable_radix)
	cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;

	/*
	* Check /chosen/ibm,architecture-vec-5 if running as a guest.
	* When running bare-metal, we can use radix if we like
	* even though the ibm,architecture-vec-5 property created by
	* skiboot doesn't have the necessary bits set.
	*/
	if (!(mfmsr() & MSR_HV))
	early_check_vec5();

	if (early_radix_enabled())
	radix__early_init_devtree();
	else
	hash__early_init_devtree();
	}
	#endif /* CONFIG_PPC_BOOK3S_64 */