/*
 * Based on arch/arm/mm/mmu.c
 *
 * Copyright (C) 1995-2005 Russell King
 * Copyright (C) 2012 ARM Ltd.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <linux/cache.h>
#include <linux/export.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/ioport.h>
#include <linux/kexec.h>
#include <linux/libfdt.h>
#include <linux/mman.h>
#include <linux/nodemask.h>
#include <linux/memblock.h>
#include <linux/memory.h>
#include <linux/fs.h>
#include <linux/io.h>
#include <linux/mm.h>
#include <linux/vmalloc.h>

#include <asm/barrier.h>
#include <asm/cputype.h>
#include <asm/fixmap.h>
#include <asm/kasan.h>
#include <asm/kernel-pgtable.h>
#include <asm/sections.h>
#include <asm/setup.h>
#include <asm/sizes.h>
#include <asm/tlb.h>
#include <asm/memblock.h>
#include <asm/mmu_context.h>
#include <asm/ptdump.h>
#include <asm/tlbflush.h>

#define NO_BLOCK_MAPPINGS       BIT(0)
#define NO_CONT_MAPPINGS        BIT(1)

u64 idmap_t0sz = TCR_T0SZ(VA_BITS_MIN);
u64 idmap_ptrs_per_pgd = PTRS_PER_PGD;

u64 __section(".mmuoff.data.write") vabits_actual;
EXPORT_SYMBOL(vabits_actual);

u64 kimage_voffset __ro_after_init;
EXPORT_SYMBOL(kimage_voffset);

/*
 * Empty_zero_page is a special page that is used for zero-initialized data
 * and COW.
 */
unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
EXPORT_SYMBOL(empty_zero_page);

static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss;
static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss __maybe_unused;
static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss __maybe_unused;

static DEFINE_SPINLOCK(swapper_pgdir_lock);

void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)
{
        pgd_t *fixmap_pgdp;

        spin_lock(&swapper_pgdir_lock);
        fixmap_pgdp = pgd_set_fixmap(__pa_symbol(pgdp));
        WRITE_ONCE(*fixmap_pgdp, pgd);
        /*
         * We need dsb(ishst) here to ensure the page-table-walker sees
         * our new entry before set_p?d() returns. The fixmap's
         * flush_tlb_kernel_range() via clear_fixmap() does this for us.
         */
        pgd_clear_fixmap();
        spin_unlock(&swapper_pgdir_lock);
}

pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
                              unsigned long size, pgprot_t vma_prot)
{
        if (!pfn_valid(pfn))
                return pgprot_noncached(vma_prot);
        else if (file->f_flags & O_SYNC)
                return pgprot_writecombine(vma_prot);
        return vma_prot;
}
EXPORT_SYMBOL(phys_mem_access_prot);

static phys_addr_t __init early_pgtable_alloc(int shift)
{
        phys_addr_t phys;
        void *ptr;

        phys = memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);

        /*
         * The FIX_{PGD,PUD,PMD} slots may be in active use, but the FIX_PTE
         * slot will be free, so we can (ab)use the FIX_PTE slot to initialise
         * any level of table.
         */
        ptr = pte_set_fixmap(phys);

        memset(ptr, 0, PAGE_SIZE);

        /*
         * Implicit barriers also ensure the zeroed page is visible to the page
         * table walker
         */
        pte_clear_fixmap();

        return phys;
}

static bool pgattr_change_is_safe(u64 old, u64 new)
{
        /*
         * The following mapping attributes may be updated in live
         * kernel mappings without the need for break-before-make.
         */
        static const pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;

        /* creating or taking down mappings is always safe */
        if (old == 0 || new == 0)
                return true;

        /* live contiguous mappings may not be manipulated at all */
        if ((old | new) & PTE_CONT)
                return false;

        /* Transitioning from Non-Global to Global is unsafe */
        if (old & ~new & PTE_NG)
                return false;

        return ((old ^ new) & ~mask) == 0;
}

static void init_pte(pmd_t *pmdp, unsigned long addr, unsigned long end,
                     phys_addr_t phys, pgprot_t prot)
{
        pte_t *ptep;

        ptep = pte_set_fixmap_offset(pmdp, addr);
        do {
                pte_t old_pte = READ_ONCE(*ptep);

                set_pte(ptep, pfn_pte(__phys_to_pfn(phys), prot));

                /*
                 * After the PTE entry has been populated once, we
                 * only allow updates to the permission attributes.
                 */
                BUG_ON(!pgattr_change_is_safe(pte_val(old_pte),
                                              READ_ONCE(pte_val(*ptep))));

                phys += PAGE_SIZE;
        } while (ptep++, addr += PAGE_SIZE, addr != end);

        pte_clear_fixmap();
}

static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
                                unsigned long end, phys_addr_t phys,
                                pgprot_t prot,
                                phys_addr_t (*pgtable_alloc)(int),
                                int flags)
{
        unsigned long next;
        pmd_t pmd = READ_ONCE(*pmdp);

        BUG_ON(pmd_sect(pmd));
        if (pmd_none(pmd)) {
                phys_addr_t pte_phys;
                BUG_ON(!pgtable_alloc);
                pte_phys = pgtable_alloc(PAGE_SHIFT);
                __pmd_populate(pmdp, pte_phys, PMD_TYPE_TABLE);
                pmd = READ_ONCE(*pmdp);
        }
        BUG_ON(pmd_bad(pmd));

        do {
                pgprot_t __prot = prot;

                next = pte_cont_addr_end(addr, end);

                /* use a contiguous mapping if the range is suitably aligned */
                if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
                    (flags & NO_CONT_MAPPINGS) == 0)
                        __prot = __pgprot(pgprot_val(prot) | PTE_CONT);

                init_pte(pmdp, addr, next, phys, __prot);

                phys += next - addr;
        } while (addr = next, addr != end);
}

static void init_pmd(pud_t *pudp, unsigned long addr, unsigned long end,
                     phys_addr_t phys, pgprot_t prot,
                     phys_addr_t (*pgtable_alloc)(int), int flags)
{
        unsigned long next;
        pmd_t *pmdp;

        pmdp = pmd_set_fixmap_offset(pudp, addr);
        do {
                pmd_t old_pmd = READ_ONCE(*pmdp);

                next = pmd_addr_end(addr, end);

                /* try section mapping first */
                if (((addr | next | phys) & ~SECTION_MASK) == 0 &&
                    (flags & NO_BLOCK_MAPPINGS) == 0) {
                        pmd_set_huge(pmdp, phys, prot);

                        /*
                         * After the PMD entry has been populated once, we
                         * only allow updates to the permission attributes.
                         */
                        BUG_ON(!pgattr_change_is_safe(pmd_val(old_pmd),
                                                      READ_ONCE(pmd_val(*pmdp))));
                } else {
                        alloc_init_cont_pte(pmdp, addr, next, phys, prot,
                                            pgtable_alloc, flags);

                        BUG_ON(pmd_val(old_pmd) != 0 &&
                               pmd_val(old_pmd) != READ_ONCE(pmd_val(*pmdp)));
                }
                phys += next - addr;
        } while (pmdp++, addr = next, addr != end);

        pmd_clear_fixmap();
}

static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr,
                                unsigned long end, phys_addr_t phys,
                                pgprot_t prot,
                                phys_addr_t (*pgtable_alloc)(int), int flags)
{
        unsigned long next;
        pud_t pud = READ_ONCE(*pudp);

        /*
         * Check for initial section mappings in the pgd/pud.
         */
        BUG_ON(pud_sect(pud));
        if (pud_none(pud)) {
                phys_addr_t pmd_phys;
                BUG_ON(!pgtable_alloc);
                pmd_phys = pgtable_alloc(PMD_SHIFT);
                __pud_populate(pudp, pmd_phys, PUD_TYPE_TABLE);
                pud = READ_ONCE(*pudp);
        }
        BUG_ON(pud_bad(pud));

        do {
                pgprot_t __prot = prot;

                next = pmd_cont_addr_end(addr, end);

                /* use a contiguous mapping if the range is suitably aligned */
                if ((((addr | next | phys) & ~CONT_PMD_MASK) == 0) &&
                    (flags & NO_CONT_MAPPINGS) == 0)
                        __prot = __pgprot(pgprot_val(prot) | PTE_CONT);

                init_pmd(pudp, addr, next, phys, __prot, pgtable_alloc, flags);

                phys += next - addr;
        } while (addr = next, addr != end);
}

static inline bool use_1G_block(unsigned long addr, unsigned long next,
                        unsigned long phys)
{
        if (PAGE_SHIFT != 12)
                return false;

        if (((addr | next | phys) & ~PUD_MASK) != 0)
                return false;

        return true;
}

static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
                           phys_addr_t phys, pgprot_t prot,
                           phys_addr_t (*pgtable_alloc)(int),
                           int flags)
{
        unsigned long next;
        pud_t *pudp;
        pgd_t pgd = READ_ONCE(*pgdp);

        if (pgd_none(pgd)) {
                phys_addr_t pud_phys;
                BUG_ON(!pgtable_alloc);
                pud_phys = pgtable_alloc(PUD_SHIFT);
                __pgd_populate(pgdp, pud_phys, PUD_TYPE_TABLE);
                pgd = READ_ONCE(*pgdp);
        }
        BUG_ON(pgd_bad(pgd));

        pudp = pud_set_fixmap_offset(pgdp, addr);
        do {
                pud_t old_pud = READ_ONCE(*pudp);

                next = pud_addr_end(addr, end);

                /*
                 * For 4K granule only, attempt to put down a 1GB block
                 */
                if (use_1G_block(addr, next, phys) &&
                    (flags & NO_BLOCK_MAPPINGS) == 0) {
                        pud_set_huge(pudp, phys, prot);

                        /*
                         * After the PUD entry has been populated once, we
                         * only allow updates to the permission attributes.
                         */
                        BUG_ON(!pgattr_change_is_safe(pud_val(old_pud),
                                                      READ_ONCE(pud_val(*pudp))));
                } else {
                        alloc_init_cont_pmd(pudp, addr, next, phys, prot,
                                            pgtable_alloc, flags);

                        BUG_ON(pud_val(old_pud) != 0 &&
                               pud_val(old_pud) != READ_ONCE(pud_val(*pudp)));
                }
                phys += next - addr;
        } while (pudp++, addr = next, addr != end);

        pud_clear_fixmap();
}

static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
                                 unsigned long virt, phys_addr_t size,
                                 pgprot_t prot,
                                 phys_addr_t (*pgtable_alloc)(int),
                                 int flags)
{
        unsigned long addr, length, end, next;
        pgd_t *pgdp = pgd_offset_raw(pgdir, virt);

        /*
         * If the virtual and physical address don't have the same offset
         * within a page, we cannot map the region as the caller expects.
         */
        if (WARN_ON((phys ^ virt) & ~PAGE_MASK))
                return;

        phys &= PAGE_MASK;
        addr = virt & PAGE_MASK;
        length = PAGE_ALIGN(size + (virt & ~PAGE_MASK));

        end = addr + length;
        do {
                next = pgd_addr_end(addr, end);
                alloc_init_pud(pgdp, addr, next, phys, prot, pgtable_alloc,
                               flags);
                phys += next - addr;
        } while (pgdp++, addr = next, addr != end);
}

static phys_addr_t __pgd_pgtable_alloc(int shift)
{
        void *ptr = (void *)__get_free_page(PGALLOC_GFP);
        BUG_ON(!ptr);

        /* Ensure the zeroed page is visible to the page table walker */
        dsb(ishst);
        return __pa(ptr);
}

static phys_addr_t pgd_pgtable_alloc(int shift)
{
        phys_addr_t pa = __pgd_pgtable_alloc(shift);

        /*
         * Call proper page table ctor in case later we need to
         * call core mm functions like apply_to_page_range() on
         * this pre-allocated page table.
         *
         * We don't select ARCH_ENABLE_SPLIT_PMD_PTLOCK if pmd is
         * folded, and if so pgtable_pmd_page_ctor() becomes nop.
         */
        if (shift == PAGE_SHIFT)
                BUG_ON(!pgtable_page_ctor(phys_to_page(pa)));
        else if (shift == PMD_SHIFT)
                BUG_ON(!pgtable_pmd_page_ctor(phys_to_page(pa)));

        return pa;
}

/*
 * This function can only be used to modify existing table entries,
 * without allocating new levels of table. Note that this permits the
 * creation of new section or page entries.
 */
static void __init create_mapping_noalloc(phys_addr_t phys, unsigned long virt,
                                  phys_addr_t size, pgprot_t prot)
{
        if ((virt >= PAGE_END) && (virt < VMALLOC_START)) {
                pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
                        &phys, virt);
                return;
        }
        __create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL,
                             NO_CONT_MAPPINGS);
}

void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
                               unsigned long virt, phys_addr_t size,
                               pgprot_t prot, bool page_mappings_only)
{
        int flags = 0;

        BUG_ON(mm == &init_mm);

        if (page_mappings_only)
                flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;

        __create_pgd_mapping(mm->pgd, phys, virt, size, prot,
                             pgd_pgtable_alloc, flags);
}

static void update_mapping_prot(phys_addr_t phys, unsigned long virt,
                                phys_addr_t size, pgprot_t prot)
{
        if ((virt >= PAGE_END) && (virt < VMALLOC_START)) {
                pr_warn("BUG: not updating mapping for %pa at 0x%016lx - outside kernel range\n",
                        &phys, virt);
                return;
        }

        __create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL,
                             NO_CONT_MAPPINGS);

        /* flush the TLBs after updating live kernel mappings */
        flush_tlb_kernel_range(virt, virt + size);
}

static void __init __map_memblock(pgd_t *pgdp, phys_addr_t start,
                                  phys_addr_t end, pgprot_t prot, int flags)
{
        __create_pgd_mapping(pgdp, start, __phys_to_virt(start), end - start,
                             prot, early_pgtable_alloc, flags);
}

void __init mark_linear_text_alias_ro(void)
{
        /*
         * Remove the write permissions from the linear alias of .text/.rodata
         */
        update_mapping_prot(__pa_symbol(_text), (unsigned long)lm_alias(_text),
                            (unsigned long)__init_begin - (unsigned long)_text,
                            PAGE_KERNEL_RO);
}

static void __init map_mem(pgd_t *pgdp)
{
        phys_addr_t kernel_start = __pa_symbol(_text);
        phys_addr_t kernel_end = __pa_symbol(__init_begin);
        struct memblock_region *reg;
        int flags = 0;

        if (rodata_full || debug_pagealloc_enabled())
                flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;

        /*
         * Take care not to create a writable alias for the
         * read-only text and rodata sections of the kernel image.
         * So temporarily mark them as NOMAP to skip mappings in
         * the following for-loop
         */
        memblock_mark_nomap(kernel_start, kernel_end - kernel_start);
#ifdef CONFIG_KEXEC_CORE
        if (crashk_res.end)
                memblock_mark_nomap(crashk_res.start,
                                    resource_size(&crashk_res));
#endif

        /* map all the memory banks */
        for_each_memblock(memory, reg) {
                phys_addr_t start = reg->base;
                phys_addr_t end = start + reg->size;

                if (start >= end)
                        break;
                if (memblock_is_nomap(reg))
                        continue;

                __map_memblock(pgdp, start, end, PAGE_KERNEL, flags);
        }

        /*
         * Map the linear alias of the [_text, __init_begin) interval
         * as non-executable now, and remove the write permission in
         * mark_linear_text_alias_ro() below (which will be called after
         * alternative patching has completed). This makes the contents
         * of the region accessible to subsystems such as hibernate,
         * but protects it from inadvertent modification or execution.
         * Note that contiguous mappings cannot be remapped in this way,
         * so we should avoid them here.
         */
        __map_memblock(pgdp, kernel_start, kernel_end,
                       PAGE_KERNEL, NO_CONT_MAPPINGS);
        memblock_clear_nomap(kernel_start, kernel_end - kernel_start);

#ifdef CONFIG_KEXEC_CORE
        /*
         * Use page-level mappings here so that we can shrink the region
         * in page granularity and put back unused memory to buddy system
         * through /sys/kernel/kexec_crash_size interface.
         */
        if (crashk_res.end) {
                __map_memblock(pgdp, crashk_res.start, crashk_res.end + 1,
                               PAGE_KERNEL,
                               NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS);
                memblock_clear_nomap(crashk_res.start,
                                     resource_size(&crashk_res));
        }
#endif
}

void mark_rodata_ro(void)
{
        unsigned long section_size;

        /*
         * mark .rodata as read only. Use __init_begin rather than __end_rodata
         * to cover NOTES and EXCEPTION_TABLE.
         */
        section_size = (unsigned long)__init_begin - (unsigned long)__start_rodata;
        update_mapping_prot(__pa_symbol(__start_rodata), (unsigned long)__start_rodata,
                            section_size, PAGE_KERNEL_RO);

        debug_checkwx();
}

static void __init map_kernel_segment(pgd_t *pgdp, void *va_start, void *va_end,
                                      pgprot_t prot, struct vm_struct *vma,
                                      int flags, unsigned long vm_flags)
{
        phys_addr_t pa_start = __pa_symbol(va_start);
        unsigned long size = va_end - va_start;

        BUG_ON(!PAGE_ALIGNED(pa_start));
        BUG_ON(!PAGE_ALIGNED(size));

        __create_pgd_mapping(pgdp, pa_start, (unsigned long)va_start, size, prot,
                             early_pgtable_alloc, flags);

        if (!(vm_flags & VM_NO_GUARD))
                size += PAGE_SIZE;

        vma->addr       = va_start;
        vma->phys_addr  = pa_start;
        vma->size       = size;
        vma->flags      = VM_MAP | vm_flags;
        vma->caller     = __builtin_return_address(0);

        vm_area_add_early(vma);
}

static int __init parse_rodata(char *arg)
{
        int ret = strtobool(arg, &rodata_enabled);
        if (!ret) {
                rodata_full = false;
                return 0;
        }

        /* permit 'full' in addition to boolean options */
        if (strcmp(arg, "full"))
                return -EINVAL;

        rodata_enabled = true;
        rodata_full = true;
        return 0;
}
early_param("rodata", parse_rodata);

#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
static int __init map_entry_trampoline(void)
{
        pgprot_t prot = rodata_enabled ? PAGE_KERNEL_ROX : PAGE_KERNEL_EXEC;
        phys_addr_t pa_start = __pa_symbol(__entry_tramp_text_start);

        /* The trampoline is always mapped and can therefore be global */
        pgprot_val(prot) &= ~PTE_NG;

        /* Map only the text into the trampoline page table */
        memset(tramp_pg_dir, 0, PGD_SIZE);
        __create_pgd_mapping(tramp_pg_dir, pa_start, TRAMP_VALIAS, PAGE_SIZE,
                             prot, __pgd_pgtable_alloc, 0);

        /* Map both the text and data into the kernel page table */
        __set_fixmap(FIX_ENTRY_TRAMP_TEXT, pa_start, prot);
        if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
                extern char __entry_tramp_data_start[];

                __set_fixmap(FIX_ENTRY_TRAMP_DATA,
                             __pa_symbol(__entry_tramp_data_start),
                             PAGE_KERNEL_RO);
        }

        return 0;
}
core_initcall(map_entry_trampoline);
#endif

/*
 * Create fine-grained mappings for the kernel.
 */
static void __init map_kernel(pgd_t *pgdp)
{
        static struct vm_struct vmlinux_text, vmlinux_rodata, vmlinux_inittext,
                                vmlinux_initdata, vmlinux_data;

        /*
         * External debuggers may need to write directly to the text
         * mapping to install SW breakpoints. Allow this (only) when
         * explicitly requested with rodata=off.
         */
        pgprot_t text_prot = rodata_enabled ? PAGE_KERNEL_ROX : PAGE_KERNEL_EXEC;

        /*
         * Only rodata will be remapped with different permissions later on,
         * all other segments are allowed to use contiguous mappings.
         */
        map_kernel_segment(pgdp, _text, _etext, text_prot, &vmlinux_text, 0,
                           VM_NO_GUARD);
        map_kernel_segment(pgdp, __start_rodata, __inittext_begin, PAGE_KERNEL,
                           &vmlinux_rodata, NO_CONT_MAPPINGS, VM_NO_GUARD);
        map_kernel_segment(pgdp, __inittext_begin, __inittext_end, text_prot,
                           &vmlinux_inittext, 0, VM_NO_GUARD);
        map_kernel_segment(pgdp, __initdata_begin, __initdata_end, PAGE_KERNEL,
                           &vmlinux_initdata, 0, VM_NO_GUARD);
        map_kernel_segment(pgdp, _data, _end, PAGE_KERNEL, &vmlinux_data, 0, 0);

        if (!READ_ONCE(pgd_val(*pgd_offset_raw(pgdp, FIXADDR_START)))) {
                /*
                 * The fixmap falls in a separate pgd to the kernel, and doesn't
                 * live in the carveout for the swapper_pg_dir. We can simply
                 * re-use the existing dir for the fixmap.
                 */
                set_pgd(pgd_offset_raw(pgdp, FIXADDR_START),
                        READ_ONCE(*pgd_offset_k(FIXADDR_START)));
        } else if (CONFIG_PGTABLE_LEVELS > 3) {
                pgd_t *bm_pgdp;
                pud_t *bm_pudp;
                /*
                 * The fixmap shares its top level pgd entry with the kernel
                 * mapping. This can really only occur when we are running
                 * with 16k/4 levels, so we can simply reuse the pud level
                 * entry instead.
                 */
                BUG_ON(!IS_ENABLED(CONFIG_ARM64_16K_PAGES));
                bm_pgdp = pgd_offset_raw(pgdp, FIXADDR_START);
                bm_pudp = pud_set_fixmap_offset(bm_pgdp, FIXADDR_START);
                pud_populate(&init_mm, bm_pudp, lm_alias(bm_pmd));
                pud_clear_fixmap();
        } else {
                BUG();
        }

        kasan_copy_shadow(pgdp);
}

/*
 * paging_init() sets up the page tables, initialises the zone memory
 * maps and sets up the zero page.
 */
void __init paging_init(void)
{
        pgd_t *pgdp = pgd_set_fixmap(__pa_symbol(swapper_pg_dir));

        map_kernel(pgdp);
        map_mem(pgdp);

        pgd_clear_fixmap();

        cpu_replace_ttbr1(lm_alias(swapper_pg_dir));
        init_mm.pgd = swapper_pg_dir;

        memblock_free(__pa_symbol(init_pg_dir),
                      __pa_symbol(init_pg_end) - __pa_symbol(init_pg_dir));
}

/*
 * Check whether a kernel address is valid (derived from arch/x86/).
 */
int kern_addr_valid(unsigned long addr)
{
        pgd_t *pgdp;
        pud_t *pudp, pud;
        pmd_t *pmdp, pmd;
        pte_t *ptep, pte;

        if ((((long)addr) >> VA_BITS) != -1UL)
                return 0;

        pgdp = pgd_offset_k(addr);
        if (pgd_none(READ_ONCE(*pgdp)))
                return 0;

        pudp = pud_offset(pgdp, addr);
        pud = READ_ONCE(*pudp);
        if (pud_none(pud))
                return 0;

        if (pud_sect(pud))
                return pfn_valid(pud_pfn(pud));

        pmdp = pmd_offset(pudp, addr);
        pmd = READ_ONCE(*pmdp);
        if (pmd_none(pmd))
                return 0;

        if (pmd_sect(pmd))
                return pfn_valid(pmd_pfn(pmd));

        ptep = pte_offset_kernel(pmdp, addr);
        pte = READ_ONCE(*ptep);
        if (pte_none(pte))
                return 0;

        return pfn_valid(pte_pfn(pte));
}

#ifdef CONFIG_MEMORY_HOTPLUG
static void free_hotplug_page_range(struct page *page, size_t size)
{
        WARN_ON(PageReserved(page));
        free_pages((unsigned long)page_address(page), get_order(size));
}

static void free_hotplug_pgtable_page(struct page *page)
{
        free_hotplug_page_range(page, PAGE_SIZE);
}

static bool pgtable_range_aligned(unsigned long start, unsigned long end,
                                  unsigned long floor, unsigned long ceiling,
                                  unsigned long mask)
{
        start &= mask;
        if (start < floor)
                return false;

        if (ceiling) {
                ceiling &= mask;
                if (!ceiling)
                        return false;
        }

        if (end - 1 > ceiling - 1)
                return false;
        return true;
}

static void unmap_hotplug_pte_range(pmd_t *pmdp, unsigned long addr,
                                    unsigned long end, bool free_mapped)
{
        pte_t *ptep, pte;

        do {
                ptep = pte_offset_kernel(pmdp, addr);
                pte = READ_ONCE(*ptep);
                if (pte_none(pte))
                        continue;

                WARN_ON(!pte_present(pte));
                pte_clear(&init_mm, addr, ptep);
                flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
                if (free_mapped)
                        free_hotplug_page_range(pte_page(pte), PAGE_SIZE);
        } while (addr += PAGE_SIZE, addr < end);
}

static void unmap_hotplug_pmd_range(pud_t *pudp, unsigned long addr,
                                    unsigned long end, bool free_mapped)
{
        unsigned long next;
        pmd_t *pmdp, pmd;

        do {
                next = pmd_addr_end(addr, end);
                pmdp = pmd_offset(pudp, addr);
                pmd = READ_ONCE(*pmdp);
                if (pmd_none(pmd))
                        continue;

                WARN_ON(!pmd_present(pmd));
                if (pmd_sect(pmd)) {
                        pmd_clear(pmdp);

                        /*
                         * One TLBI should be sufficient here as the PMD_SIZE
                         * range is mapped with a single block entry.
                         */
                        flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
                        if (free_mapped)
                                free_hotplug_page_range(pmd_page(pmd),
                                                        PMD_SIZE);
                        continue;
                }
                WARN_ON(!pmd_table(pmd));
                unmap_hotplug_pte_range(pmdp, addr, next, free_mapped);
        } while (addr = next, addr < end);
}

static void unmap_hotplug_pud_range(p4d_t *p4dp, unsigned long addr,
                                    unsigned long end, bool free_mapped)
{
        unsigned long next;
        pud_t *pudp, pud;

        do {
                next = pud_addr_end(addr, end);
                pudp = pud_offset(p4dp, addr);
                pud = READ_ONCE(*pudp);
                if (pud_none(pud))
                        continue;

                WARN_ON(!pud_present(pud));
                if (pud_sect(pud)) {
                        pud_clear(pudp);

                        /*
                         * One TLBI should be sufficient here as the PUD_SIZE
                         * range is mapped with a single block entry.
                         */
                        flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
                        if (free_mapped)
                                free_hotplug_page_range(pud_page(pud),
                                                        PUD_SIZE);
                        continue;
                }
                WARN_ON(!pud_table(pud));
                unmap_hotplug_pmd_range(pudp, addr, next, free_mapped);
        } while (addr = next, addr < end);
}

static void unmap_hotplug_p4d_range(pgd_t *pgdp, unsigned long addr,
                                    unsigned long end, bool free_mapped)
{
        unsigned long next;
        p4d_t *p4dp, p4d;

        do {
                next = p4d_addr_end(addr, end);
                p4dp = p4d_offset(pgdp, addr);
                p4d = READ_ONCE(*p4dp);
                if (p4d_none(p4d))
                        continue;

                WARN_ON(!p4d_present(p4d));
                unmap_hotplug_pud_range(p4dp, addr, next, free_mapped);
        } while (addr = next, addr < end);
}

static void unmap_hotplug_range(unsigned long addr, unsigned long end,
                                bool free_mapped)
{
        unsigned long next;
        pgd_t *pgdp, pgd;

        do {
                next = pgd_addr_end(addr, end);
                pgdp = pgd_offset_k(addr);
                pgd = READ_ONCE(*pgdp);
                if (pgd_none(pgd))
                        continue;

                WARN_ON(!pgd_present(pgd));
                unmap_hotplug_p4d_range(pgdp, addr, next, free_mapped);
        } while (addr = next, addr < end);
}

static void free_empty_pte_table(pmd_t *pmdp, unsigned long addr,
                                 unsigned long end, unsigned long floor,
                                 unsigned long ceiling)
{
        pte_t *ptep, pte;
        unsigned long i, start = addr;

        do {
                ptep = pte_offset_kernel(pmdp, addr);
                pte = READ_ONCE(*ptep);

                /*
                 * This is just a sanity check here which verifies that
                 * pte clearing has been done by earlier unmap loops.
                 */
                WARN_ON(!pte_none(pte));
        } while (addr += PAGE_SIZE, addr < end);

        if (!pgtable_range_aligned(start, end, floor, ceiling, PMD_MASK))
                return;

        /*
         * Check whether we can free the pte page if the rest of the
         * entries are empty. Overlap with other regions have been
         * handled by the floor/ceiling check.
         */
        ptep = pte_offset_kernel(pmdp, 0UL);
        for (i = 0; i < PTRS_PER_PTE; i++) {
                if (!pte_none(READ_ONCE(ptep[i])))
                        return;
        }

        pmd_clear(pmdp);
        __flush_tlb_kernel_pgtable(start);
        free_hotplug_pgtable_page(virt_to_page(ptep));
}

static void free_empty_pmd_table(pud_t *pudp, unsigned long addr,
                                 unsigned long end, unsigned long floor,
                                 unsigned long ceiling)
{
        pmd_t *pmdp, pmd;
        unsigned long i, next, start = addr;

        do {
                next = pmd_addr_end(addr, end);
                pmdp = pmd_offset(pudp, addr);
                pmd = READ_ONCE(*pmdp);
                if (pmd_none(pmd))
                        continue;

                WARN_ON(!pmd_present(pmd) || !pmd_table(pmd) || pmd_sect(pmd));
                free_empty_pte_table(pmdp, addr, next, floor, ceiling);
        } while (addr = next, addr < end);

        if (CONFIG_PGTABLE_LEVELS <= 2)
                return;

        if (!pgtable_range_aligned(start, end, floor, ceiling, PUD_MASK))
                return;

        /*
         * Check whether we can free the pmd page if the rest of the
         * entries are empty. Overlap with other regions have been
         * handled by the floor/ceiling check.
         */
        pmdp = pmd_offset(pudp, 0UL);
        for (i = 0; i < PTRS_PER_PMD; i++) {
                if (!pmd_none(READ_ONCE(pmdp[i])))
                        return;
        }

        pud_clear(pudp);
        __flush_tlb_kernel_pgtable(start);
        free_hotplug_pgtable_page(virt_to_page(pmdp));
}

static void free_empty_pud_table(p4d_t *p4dp, unsigned long addr,
                                 unsigned long end, unsigned long floor,
                                 unsigned long ceiling)
{
        pud_t *pudp, pud;
        unsigned long i, next, start = addr;

        do {
                next = pud_addr_end(addr, end);
                pudp = pud_offset(p4dp, addr);
                pud = READ_ONCE(*pudp);
                if (pud_none(pud))
                        continue;

                WARN_ON(!pud_present(pud) || !pud_table(pud) || pud_sect(pud));
                free_empty_pmd_table(pudp, addr, next, floor, ceiling);
        } while (addr = next, addr < end);

        if (CONFIG_PGTABLE_LEVELS <= 3)
                return;

        if (!pgtable_range_aligned(start, end, floor, ceiling, PGDIR_MASK))
                return;

        /*
         * Check whether we can free the pud page if the rest of the
         * entries are empty. Overlap with other regions have been
         * handled by the floor/ceiling check.
         */
        pudp = pud_offset(p4dp, 0UL);
        for (i = 0; i < PTRS_PER_PUD; i++) {
                if (!pud_none(READ_ONCE(pudp[i])))

                        return;
        }

        p4d_clear(p4dp);
        __flush_tlb_kernel_pgtable(start);
        free_hotplug_pgtable_page(virt_to_page(pudp));
}

static void free_empty_p4d_table(pgd_t *pgdp, unsigned long addr,
                                 unsigned long end, unsigned long floor,
                                 unsigned long ceiling)
{
        unsigned long next;
        p4d_t *p4dp, p4d;

        do {
                next = p4d_addr_end(addr, end);
                p4dp = p4d_offset(pgdp, addr);
                p4d = READ_ONCE(*p4dp);
                if (p4d_none(p4d))
                        continue;

                WARN_ON(!p4d_present(p4d));
                free_empty_pud_table(p4dp, addr, next, floor, ceiling);
        } while (addr = next, addr < end);
}

static void free_empty_tables(unsigned long addr, unsigned long end,
                              unsigned long floor, unsigned long ceiling)
{
        unsigned long next;
        pgd_t *pgdp, pgd;

        do {
                next = pgd_addr_end(addr, end);
                pgdp = pgd_offset_k(addr);
                pgd = READ_ONCE(*pgdp);
                if (pgd_none(pgd))
                        continue;

                WARN_ON(!pgd_present(pgd));
                free_empty_p4d_table(pgdp, addr, next, floor, ceiling);
        } while (addr = next, addr < end);
}
#endif

#ifdef CONFIG_SPARSEMEM_VMEMMAP
#if !ARM64_SWAPPER_USES_SECTION_MAPS
int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
                struct vmem_altmap *altmap)
{
        return vmemmap_populate_basepages(start, end, node);
}
#else   /* !ARM64_SWAPPER_USES_SECTION_MAPS */
int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
                struct vmem_altmap *altmap)
{
        unsigned long addr = start;
        unsigned long next;
        pgd_t *pgdp;
        pud_t *pudp;
        pmd_t *pmdp;

        do {
                next = pmd_addr_end(addr, end);

                pgdp = vmemmap_pgd_populate(addr, node);
                if (!pgdp)
                        return -ENOMEM;

                pudp = vmemmap_pud_populate(pgdp, addr, node);
                if (!pudp)
                        return -ENOMEM;

                pmdp = pmd_offset(pudp, addr);
                if (pmd_none(READ_ONCE(*pmdp))) {
                        void *p = NULL;

                        p = vmemmap_alloc_block_buf(PMD_SIZE, node);
                        if (!p)
                                return -ENOMEM;

                        pmd_set_huge(pmdp, __pa(p), __pgprot(PROT_SECT_NORMAL));
                } else
                        vmemmap_verify((pte_t *)pmdp, node, addr, next);
        } while (addr = next, addr != end);

        return 0;
}
#endif  /* CONFIG_ARM64_64K_PAGES */
void vmemmap_free(unsigned long start, unsigned long end,
                struct vmem_altmap *altmap)
{
#ifdef CONFIG_MEMORY_HOTPLUG
        WARN_ON((start < VMEMMAP_START) || (end > VMEMMAP_END));

        unmap_hotplug_range(start, end, true);
        free_empty_tables(start, end, VMEMMAP_START, VMEMMAP_END);
#endif
}
#endif  /* CONFIG_SPARSEMEM_VMEMMAP */

static inline pud_t * fixmap_pud(unsigned long addr)
{
        pgd_t *pgdp = pgd_offset_k(addr);
        pgd_t pgd = READ_ONCE(*pgdp);

        BUG_ON(pgd_none(pgd) || pgd_bad(pgd));

        return pud_offset_kimg(pgdp, addr);
}

static inline pmd_t * fixmap_pmd(unsigned long addr)
{
        pud_t *pudp = fixmap_pud(addr);
        pud_t pud = READ_ONCE(*pudp);

        BUG_ON(pud_none(pud) || pud_bad(pud));

        return pmd_offset_kimg(pudp, addr);
}

static inline pte_t * fixmap_pte(unsigned long addr)
{
        return &bm_pte[pte_index(addr)];
}

/*
 * The p*d_populate functions call virt_to_phys implicitly so they can't be used
 * directly on kernel symbols (bm_p*d). This function is called too early to use
 * lm_alias so __p*d_populate functions must be used to populate with the
 * physical address from __pa_symbol.
 */
void __init early_fixmap_init(void)
{
        pgd_t *pgdp, pgd;
        pud_t *pudp;
        pmd_t *pmdp;
        unsigned long addr = FIXADDR_START;

        pgdp = pgd_offset_k(addr);
        pgd = READ_ONCE(*pgdp);
        if (CONFIG_PGTABLE_LEVELS > 3 &&
            !(pgd_none(pgd) || pgd_page_paddr(pgd) == __pa_symbol(bm_pud))) {
                /*
                 * We only end up here if the kernel mapping and the fixmap
                 * share the top level pgd entry, which should only happen on
                 * 16k/4 levels configurations.
                 */
                BUG_ON(!IS_ENABLED(CONFIG_ARM64_16K_PAGES));
                pudp = pud_offset_kimg(pgdp, addr);
        } else {
                if (pgd_none(pgd))
                        __pgd_populate(pgdp, __pa_symbol(bm_pud), PUD_TYPE_TABLE);
                pudp = fixmap_pud(addr);
        }
        if (pud_none(READ_ONCE(*pudp)))
                __pud_populate(pudp, __pa_symbol(bm_pmd), PMD_TYPE_TABLE);
        pmdp = fixmap_pmd(addr);
        __pmd_populate(pmdp, __pa_symbol(bm_pte), PMD_TYPE_TABLE);

        /*
         * The boot-ioremap range spans multiple pmds, for which
         * we are not prepared:
         */
        BUILD_BUG_ON((__fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT)
                     != (__fix_to_virt(FIX_BTMAP_END) >> PMD_SHIFT));

        if ((pmdp != fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)))
             || pmdp != fixmap_pmd(fix_to_virt(FIX_BTMAP_END))) {
                WARN_ON(1);
                pr_warn("pmdp %p != %p, %p\n",
                        pmdp, fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)),
                        fixmap_pmd(fix_to_virt(FIX_BTMAP_END)));
                pr_warn("fix_to_virt(FIX_BTMAP_BEGIN): %08lx\n",
                        fix_to_virt(FIX_BTMAP_BEGIN));
                pr_warn("fix_to_virt(FIX_BTMAP_END):   %08lx\n",
                        fix_to_virt(FIX_BTMAP_END));

                pr_warn("FIX_BTMAP_END:       %d\n", FIX_BTMAP_END);
                pr_warn("FIX_BTMAP_BEGIN:     %d\n", FIX_BTMAP_BEGIN);
        }
}

/*
 * Unusually, this is also called in IRQ context (ghes_iounmap_irq) so if we
 * ever need to use IPIs for TLB broadcasting, then we're in trouble here.
 */
void __set_fixmap(enum fixed_addresses idx,
                               phys_addr_t phys, pgprot_t flags)
{
        unsigned long addr = __fix_to_virt(idx);
        pte_t *ptep;

        BUG_ON(idx <= FIX_HOLE || idx >= __end_of_fixed_addresses);

        ptep = fixmap_pte(addr);

        if (pgprot_val(flags)) {
                set_pte(ptep, pfn_pte(phys >> PAGE_SHIFT, flags));
        } else {
                pte_clear(&init_mm, addr, ptep);
                flush_tlb_kernel_range(addr, addr+PAGE_SIZE);
        }
}

void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot)
{
        const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
        int offset;
        void *dt_virt;

        /*
         * Check whether the physical FDT address is set and meets the minimum
         * alignment requirement. Since we are relying on MIN_FDT_ALIGN to be
         * at least 8 bytes so that we can always access the magic and size
         * fields of the FDT header after mapping the first chunk, double check
         * here if that is indeed the case.
         */
        BUILD_BUG_ON(MIN_FDT_ALIGN < 8);
        if (!dt_phys || dt_phys % MIN_FDT_ALIGN)
                return NULL;

        /*
         * Make sure that the FDT region can be mapped without the need to
         * allocate additional translation table pages, so that it is safe
         * to call create_mapping_noalloc() this early.
         *
         * On 64k pages, the FDT will be mapped using PTEs, so we need to
         * be in the same PMD as the rest of the fixmap.
         * On 4k pages, we'll use section mappings for the FDT so we only
         * have to be in the same PUD.
         */
        BUILD_BUG_ON(dt_virt_base % SZ_2M);

        BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> SWAPPER_TABLE_SHIFT !=
                     __fix_to_virt(FIX_BTMAP_BEGIN) >> SWAPPER_TABLE_SHIFT);

        offset = dt_phys % SWAPPER_BLOCK_SIZE;
        dt_virt = (void *)dt_virt_base + offset;

        /* map the first chunk so we can read the size from the header */
        create_mapping_noalloc(round_down(dt_phys, SWAPPER_BLOCK_SIZE),
                        dt_virt_base, SWAPPER_BLOCK_SIZE, prot);

        if (fdt_magic(dt_virt) != FDT_MAGIC)
                return NULL;

        *size = fdt_totalsize(dt_virt);
        if (*size > MAX_FDT_SIZE)
                return NULL;

        if (offset + *size > SWAPPER_BLOCK_SIZE)
                create_mapping_noalloc(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
                               round_up(offset + *size, SWAPPER_BLOCK_SIZE), prot);

        return dt_virt;
}

void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
{
        void *dt_virt;
        int size;

        dt_virt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL_RO);
        if (!dt_virt)
                return NULL;

        memblock_reserve(dt_phys, size);
        return dt_virt;
}

int __init arch_ioremap_pud_supported(void)
{
        /*
         * Only 4k granule supports level 1 block mappings.
         * SW table walks can't handle removal of intermediate entries.
         */
        return IS_ENABLED(CONFIG_ARM64_4K_PAGES) &&
               !IS_ENABLED(CONFIG_PTDUMP_DEBUGFS);
}

int __init arch_ioremap_pmd_supported(void)
{
        /* See arch_ioremap_pud_supported() */
        return !IS_ENABLED(CONFIG_PTDUMP_DEBUGFS);
}

int pud_set_huge(pud_t *pudp, phys_addr_t phys, pgprot_t prot)
{
        pgprot_t sect_prot = __pgprot(PUD_TYPE_SECT |
                                        pgprot_val(mk_sect_prot(prot)));
        pud_t new_pud = pfn_pud(__phys_to_pfn(phys), sect_prot);

        /* Only allow permission changes for now */
        if (!pgattr_change_is_safe(READ_ONCE(pud_val(*pudp)),
                                   pud_val(new_pud)))
                return 0;

        BUG_ON(phys & ~PUD_MASK);
        set_pud(pudp, new_pud);
        return 1;
}

int pmd_set_huge(pmd_t *pmdp, phys_addr_t phys, pgprot_t prot)
{
        pgprot_t sect_prot = __pgprot(PMD_TYPE_SECT |
                                        pgprot_val(mk_sect_prot(prot)));
        pmd_t new_pmd = pfn_pmd(__phys_to_pfn(phys), sect_prot);

        /* Only allow permission changes for now */
        if (!pgattr_change_is_safe(READ_ONCE(pmd_val(*pmdp)),
                                   pmd_val(new_pmd)))
                return 0;

        BUG_ON(phys & ~PMD_MASK);
        set_pmd(pmdp, new_pmd);
        return 1;
}

int pud_clear_huge(pud_t *pudp)
{
        if (!pud_sect(READ_ONCE(*pudp)))
                return 0;
        pud_clear(pudp);
        return 1;
}

int pmd_clear_huge(pmd_t *pmdp)
{
        if (!pmd_sect(READ_ONCE(*pmdp)))
                return 0;
        pmd_clear(pmdp);
        return 1;
}

int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)
{
        pte_t *table;
        pmd_t pmd;

        pmd = READ_ONCE(*pmdp);

        if (!pmd_present(pmd))
                return 1;
        if (!pmd_table(pmd)) {
                VM_WARN_ON(!pmd_table(pmd));
                return 1;
        }

        table = pte_offset_kernel(pmdp, addr);
        pmd_clear(pmdp);
        __flush_tlb_kernel_pgtable(addr);
        pte_free_kernel(NULL, table);
        return 1;
}

int pud_free_pmd_page(pud_t *pudp, unsigned long addr)
{
        pmd_t *table;
        pmd_t *pmdp;
        pud_t pud;
        unsigned long next, end;

        pud = READ_ONCE(*pudp);

        if (!pud_present(pud))
                return 1;
        if (!pud_table(pud)) {
                VM_WARN_ON(!pud_table(pud));
                return 1;
        }

        table = pmd_offset(pudp, addr);
        pmdp = table;
        next = addr;
        end = addr + PUD_SIZE;
        do {
                pmd_free_pte_page(pmdp, next);
        } while (pmdp++, next += PMD_SIZE, next != end);

        pud_clear(pudp);
        __flush_tlb_kernel_pgtable(addr);
        pmd_free(NULL, table);
        return 1;
}

#ifdef CONFIG_MEMORY_HOTPLUG
static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long start, u64 size)
{
        unsigned long end = start + size;

        WARN_ON(pgdir != init_mm.pgd);
        WARN_ON((start < PAGE_OFFSET) || (end > PAGE_END));

        unmap_hotplug_range(start, end, false);
        free_empty_tables(start, end, PAGE_OFFSET, PAGE_END);
}

int arch_add_memory(int nid, u64 start, u64 size,
                    struct mhp_params *params)
{
        int ret, flags = 0;

        if (rodata_full || debug_pagealloc_enabled())
                flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;

        __create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start),
                             size, params->pgprot, __pgd_pgtable_alloc,
                             flags);

        memblock_clear_nomap(start, size);

        ret = __add_pages(nid, start >> PAGE_SHIFT, size >> PAGE_SHIFT,
                           params);
        if (ret)
                __remove_pgd_mapping(swapper_pg_dir,
                                     __phys_to_virt(start), size);
        return ret;
}

void arch_remove_memory(int nid, u64 start, u64 size,
                        struct vmem_altmap *altmap)
{
        unsigned long start_pfn = start >> PAGE_SHIFT;
        unsigned long nr_pages = size >> PAGE_SHIFT;

        __remove_pages(start_pfn, nr_pages, altmap);
        __remove_pgd_mapping(swapper_pg_dir, __phys_to_virt(start), size);
}

/*
 * This memory hotplug notifier helps prevent boot memory from being
 * inadvertently removed as it blocks pfn range offlining process in
 * __offline_pages(). Hence this prevents both offlining as well as
 * removal process for boot memory which is initially always online.
 * In future if and when boot memory could be removed, this notifier
 * should be dropped and free_hotplug_page_range() should handle any
 * reserved pages allocated during boot.
 */
static int prevent_bootmem_remove_notifier(struct notifier_block *nb,
                                           unsigned long action, void *data)
{
        struct mem_section *ms;
        struct memory_notify *arg = data;
        unsigned long end_pfn = arg->start_pfn + arg->nr_pages;
        unsigned long pfn = arg->start_pfn;

        if (action != MEM_GOING_OFFLINE)
                return NOTIFY_OK;

        for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
                ms = __pfn_to_section(pfn);
                if (early_section(ms))
                        return NOTIFY_BAD;
        }
        return NOTIFY_OK;
}

static struct notifier_block prevent_bootmem_remove_nb = {
        .notifier_call = prevent_bootmem_remove_notifier,
};

static int __init prevent_bootmem_remove_init(void)
{
        return register_memory_notifier(&prevent_bootmem_remove_nb);
}
device_initcall(prevent_bootmem_remove_init);
#endif