/*
 * kexec.c - kexec system call core code.
 * Copyright (C) 2002-2004 Eric Biederman  <ebiederm@xmission.com>
 *
 * This source code is licensed under the GNU General Public License,
 * Version 2.  See the file COPYING for more details.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/capability.h>
#include <linux/mm.h>
#include <linux/file.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/kexec.h>
#include <linux/mutex.h>
#include <linux/list.h>
#include <linux/highmem.h>
#include <linux/syscalls.h>
#include <linux/reboot.h>
#include <linux/ioport.h>
#include <linux/hardirq.h>
#include <linux/elf.h>
#include <linux/elfcore.h>
#include <linux/utsname.h>
#include <linux/numa.h>
#include <linux/suspend.h>
#include <linux/device.h>
#include <linux/freezer.h>
#include <linux/pm.h>
#include <linux/cpu.h>
#include <linux/uaccess.h>
#include <linux/io.h>
#include <linux/console.h>
#include <linux/vmalloc.h>
#include <linux/swap.h>
#include <linux/syscore_ops.h>
#include <linux/compiler.h>
#include <linux/hugetlb.h>
#include <linux/frame.h>

#include <asm/page.h>
#include <asm/sections.h>

#include <crypto/hash.h>
#include <crypto/sha.h>
#include "kexec_internal.h"

DEFINE_MUTEX(kexec_mutex);

/* Per cpu memory for storing cpu states in case of system crash. */
note_buf_t __percpu *crash_notes;

/* Flag to indicate we are going to kexec a new kernel */
bool kexec_in_progress = false;


/* Location of the reserved area for the crash kernel */
struct resource crashk_res = {
        .name  = "Crash kernel",
        .start = 0,
        .end   = 0,
        .flags = IORESOURCE_BUSY | IORESOURCE_SYSTEM_RAM,
        .desc  = IORES_DESC_CRASH_KERNEL
};
struct resource crashk_low_res = {
        .name  = "Crash kernel",
        .start = 0,
        .end   = 0,
        .flags = IORESOURCE_BUSY | IORESOURCE_SYSTEM_RAM,
        .desc  = IORES_DESC_CRASH_KERNEL
};

int kexec_should_crash(struct task_struct *p)
{
        /*
         * If crash_kexec_post_notifiers is enabled, don't run
         * crash_kexec() here yet, which must be run after panic
         * notifiers in panic().
         */
        if (crash_kexec_post_notifiers)
                return 0;
        /*
         * There are 4 panic() calls in do_exit() path, each of which
         * corresponds to each of these 4 conditions.
         */
        if (in_interrupt() || !p->pid || is_global_init(p) || panic_on_oops)
                return 1;
        return 0;
}

int kexec_crash_loaded(void)
{
        return !!kexec_crash_image;
}
EXPORT_SYMBOL_GPL(kexec_crash_loaded);

/*
 * When kexec transitions to the new kernel there is a one-to-one
 * mapping between physical and virtual addresses.  On processors
 * where you can disable the MMU this is trivial, and easy.  For
 * others it is still a simple predictable page table to setup.
 *
 * In that environment kexec copies the new kernel to its final
 * resting place.  This means I can only support memory whose
 * physical address can fit in an unsigned long.  In particular
 * addresses where (pfn << PAGE_SHIFT) > ULONG_MAX cannot be handled.
 * If the assembly stub has more restrictive requirements
 * KEXEC_SOURCE_MEMORY_LIMIT and KEXEC_DEST_MEMORY_LIMIT can be
 * defined more restrictively in <asm/kexec.h>.
 *
 * The code for the transition from the current kernel to the
 * the new kernel is placed in the control_code_buffer, whose size
 * is given by KEXEC_CONTROL_PAGE_SIZE.  In the best case only a single
 * page of memory is necessary, but some architectures require more.
 * Because this memory must be identity mapped in the transition from
 * virtual to physical addresses it must live in the range
 * 0 - TASK_SIZE, as only the user space mappings are arbitrarily
 * modifiable.
 *
 * The assembly stub in the control code buffer is passed a linked list
 * of descriptor pages detailing the source pages of the new kernel,
 * and the destination addresses of those source pages.  As this data
 * structure is not used in the context of the current OS, it must
 * be self-contained.
 *
 * The code has been made to work with highmem pages and will use a
 * destination page in its final resting place (if it happens
 * to allocate it).  The end product of this is that most of the
 * physical address space, and most of RAM can be used.
 *
 * Future directions include:
 *  - allocating a page table with the control code buffer identity
 *    mapped, to simplify machine_kexec and make kexec_on_panic more
 *    reliable.
 */

/*
 * KIMAGE_NO_DEST is an impossible destination address..., for
 * allocating pages whose destination address we do not care about.
 */
#define KIMAGE_NO_DEST (-1UL)
#define PAGE_COUNT(x) (((x) + PAGE_SIZE - 1) >> PAGE_SHIFT)

static struct page *kimage_alloc_page(struct kimage *image,
                                       gfp_t gfp_mask,
                                       unsigned long dest);

int sanity_check_segment_list(struct kimage *image)
{
        int i;
        unsigned long nr_segments = image->nr_segments;
        unsigned long total_pages = 0;

        /*
         * Verify we have good destination addresses.  The caller is
         * responsible for making certain we don't attempt to load
         * the new image into invalid or reserved areas of RAM.  This
         * just verifies it is an address we can use.
         *
         * Since the kernel does everything in page size chunks ensure
         * the destination addresses are page aligned.  Too many
         * special cases crop of when we don't do this.  The most
         * insidious is getting overlapping destination addresses
         * simply because addresses are changed to page size
         * granularity.
         */
        for (i = 0; i < nr_segments; i++) {
                unsigned long mstart, mend;

                mstart = image->segment[i].mem;
                mend   = mstart + image->segment[i].memsz;
                if (mstart > mend)
                        return -EADDRNOTAVAIL;
                if ((mstart & ~PAGE_MASK) || (mend & ~PAGE_MASK))
                        return -EADDRNOTAVAIL;
                if (mend >= KEXEC_DESTINATION_MEMORY_LIMIT)
                        return -EADDRNOTAVAIL;
        }

        /* Verify our destination addresses do not overlap.
         * If we alloed overlapping destination addresses
         * through very weird things can happen with no
         * easy explanation as one segment stops on another.
         */
        for (i = 0; i < nr_segments; i++) {
                unsigned long mstart, mend;
                unsigned long j;

                mstart = image->segment[i].mem;
                mend   = mstart + image->segment[i].memsz;
                for (j = 0; j < i; j++) {
                        unsigned long pstart, pend;

                        pstart = image->segment[j].mem;
                        pend   = pstart + image->segment[j].memsz;
                        /* Do the segments overlap ? */
                        if ((mend > pstart) && (mstart < pend))
                                return -EINVAL;
                }
        }

        /* Ensure our buffer sizes are strictly less than
         * our memory sizes.  This should always be the case,
         * and it is easier to check up front than to be surprised
         * later on.
         */
        for (i = 0; i < nr_segments; i++) {
                if (image->segment[i].bufsz > image->segment[i].memsz)
                        return -EINVAL;
        }

        /*
         * Verify that no more than half of memory will be consumed. If the
         * request from userspace is too large, a large amount of time will be
         * wasted allocating pages, which can cause a soft lockup.
         */
        for (i = 0; i < nr_segments; i++) {
                if (PAGE_COUNT(image->segment[i].memsz) > totalram_pages / 2)
                        return -EINVAL;

                total_pages += PAGE_COUNT(image->segment[i].memsz);
        }

        if (total_pages > totalram_pages / 2)
                return -EINVAL;

        /*
         * Verify we have good destination addresses.  Normally
         * the caller is responsible for making certain we don't
         * attempt to load the new image into invalid or reserved
         * areas of RAM.  But crash kernels are preloaded into a
         * reserved area of ram.  We must ensure the addresses
         * are in the reserved area otherwise preloading the
         * kernel could corrupt things.
         */

        if (image->type == KEXEC_TYPE_CRASH) {
                for (i = 0; i < nr_segments; i++) {
                        unsigned long mstart, mend;

                        mstart = image->segment[i].mem;
                        mend = mstart + image->segment[i].memsz - 1;
                        /* Ensure we are within the crash kernel limits */
                        if ((mstart < phys_to_boot_phys(crashk_res.start)) ||
                            (mend > phys_to_boot_phys(crashk_res.end)))
                                return -EADDRNOTAVAIL;
                }
        }

        return 0;
}

struct kimage *do_kimage_alloc_init(void)
{
        struct kimage *image;

        /* Allocate a controlling structure */
        image = kzalloc(sizeof(*image), GFP_KERNEL);
        if (!image)
                return NULL;

        image->head = 0;
        image->entry = &image->head;
        image->last_entry = &image->head;
        image->control_page = ~0; /* By default this does not apply */
        image->type = KEXEC_TYPE_DEFAULT;

        /* Initialize the list of control pages */
        INIT_LIST_HEAD(&image->control_pages);

        /* Initialize the list of destination pages */
        INIT_LIST_HEAD(&image->dest_pages);

        /* Initialize the list of unusable pages */
        INIT_LIST_HEAD(&image->unusable_pages);

        return image;
}

int kimage_is_destination_range(struct kimage *image,
                                        unsigned long start,
                                        unsigned long end)
{
        unsigned long i;

        for (i = 0; i < image->nr_segments; i++) {
                unsigned long mstart, mend;

                mstart = image->segment[i].mem;
                mend = mstart + image->segment[i].memsz;
                if ((end > mstart) && (start < mend))
                        return 1;
        }

        return 0;
}

static struct page *kimage_alloc_pages(gfp_t gfp_mask, unsigned int order)
{
        struct page *pages;

        pages = alloc_pages(gfp_mask & ~__GFP_ZERO, order);
        if (pages) {
                unsigned int count, i;

                pages->mapping = NULL;
                set_page_private(pages, order);
                count = 1 << order;
                for (i = 0; i < count; i++)
                        SetPageReserved(pages + i);

                arch_kexec_post_alloc_pages(page_address(pages), count,
                                            gfp_mask);

                if (gfp_mask & __GFP_ZERO)
                        for (i = 0; i < count; i++)
                                clear_highpage(pages + i);
        }

        return pages;
}

static void kimage_free_pages(struct page *page)
{
        unsigned int order, count, i;

        order = page_private(page);
        count = 1 << order;

        arch_kexec_pre_free_pages(page_address(page), count);

        for (i = 0; i < count; i++)
                ClearPageReserved(page + i);
        __free_pages(page, order);
}

void kimage_free_page_list(struct list_head *list)
{
        struct page *page, *next;

        list_for_each_entry_safe(page, next, list, lru) {
                list_del(&page->lru);
                kimage_free_pages(page);
        }
}

static struct page *kimage_alloc_normal_control_pages(struct kimage *image,
                                                        unsigned int order)
{
        /* Control pages are special, they are the intermediaries
         * that are needed while we copy the rest of the pages
         * to their final resting place.  As such they must
         * not conflict with either the destination addresses
         * or memory the kernel is already using.
         *
         * The only case where we really need more than one of
         * these are for architectures where we cannot disable
         * the MMU and must instead generate an identity mapped
         * page table for all of the memory.
         *
         * At worst this runs in O(N) of the image size.
         */
        struct list_head extra_pages;
        struct page *pages;
        unsigned int count;

        count = 1 << order;
        INIT_LIST_HEAD(&extra_pages);

        /* Loop while I can allocate a page and the page allocated
         * is a destination page.
         */
        do {
                unsigned long pfn, epfn, addr, eaddr;

                pages = kimage_alloc_pages(KEXEC_CONTROL_MEMORY_GFP, order);
                if (!pages)
                        break;
                pfn   = page_to_boot_pfn(pages);
                epfn  = pfn + count;
                addr  = pfn << PAGE_SHIFT;
                eaddr = epfn << PAGE_SHIFT;
                if ((epfn >= (KEXEC_CONTROL_MEMORY_LIMIT >> PAGE_SHIFT)) ||
                              kimage_is_destination_range(image, addr, eaddr)) {
                        list_add(&pages->lru, &extra_pages);
                        pages = NULL;
                }
        } while (!pages);

        if (pages) {
                /* Remember the allocated page... */
                list_add(&pages->lru, &image->control_pages);

                /* Because the page is already in it's destination
                 * location we will never allocate another page at
                 * that address.  Therefore kimage_alloc_pages
                 * will not return it (again) and we don't need
                 * to give it an entry in image->segment[].
                 */
        }
        /* Deal with the destination pages I have inadvertently allocated.
         *
         * Ideally I would convert multi-page allocations into single
         * page allocations, and add everything to image->dest_pages.
         *
         * For now it is simpler to just free the pages.
         */
        kimage_free_page_list(&extra_pages);

        return pages;
}

static struct page *kimage_alloc_crash_control_pages(struct kimage *image,
                                                      unsigned int order)
{
        /* Control pages are special, they are the intermediaries
         * that are needed while we copy the rest of the pages
         * to their final resting place.  As such they must
         * not conflict with either the destination addresses
         * or memory the kernel is already using.
         *
         * Control pages are also the only pags we must allocate
         * when loading a crash kernel.  All of the other pages
         * are specified by the segments and we just memcpy
         * into them directly.
         *
         * The only case where we really need more than one of
         * these are for architectures where we cannot disable
         * the MMU and must instead generate an identity mapped
         * page table for all of the memory.
         *
         * Given the low demand this implements a very simple
         * allocator that finds the first hole of the appropriate
         * size in the reserved memory region, and allocates all
         * of the memory up to and including the hole.
         */
        unsigned long hole_start, hole_end, size;
        struct page *pages;

        pages = NULL;
        size = (1 << order) << PAGE_SHIFT;
        hole_start = (image->control_page + (size - 1)) & ~(size - 1);
        hole_end   = hole_start + size - 1;
        while (hole_end <= crashk_res.end) {
                unsigned long i;

                cond_resched();

                if (hole_end > KEXEC_CRASH_CONTROL_MEMORY_LIMIT)
                        break;
                /* See if I overlap any of the segments */
                for (i = 0; i < image->nr_segments; i++) {
                        unsigned long mstart, mend;

                        mstart = image->segment[i].mem;
                        mend   = mstart + image->segment[i].memsz - 1;
                        if ((hole_end >= mstart) && (hole_start <= mend)) {
                                /* Advance the hole to the end of the segment */
                                hole_start = (mend + (size - 1)) & ~(size - 1);
                                hole_end   = hole_start + size - 1;
                                break;
                        }
                }
                /* If I don't overlap any segments I have found my hole! */
                if (i == image->nr_segments) {
                        pages = pfn_to_page(hole_start >> PAGE_SHIFT);
                        image->control_page = hole_end;
                        break;
                }
        }

        return pages;
}


struct page *kimage_alloc_control_pages(struct kimage *image,
                                         unsigned int order)
{
        struct page *pages = NULL;

        switch (image->type) {
        case KEXEC_TYPE_DEFAULT:
                pages = kimage_alloc_normal_control_pages(image, order);
                break;
        case KEXEC_TYPE_CRASH:
                pages = kimage_alloc_crash_control_pages(image, order);
                break;
        }

        return pages;
}

int kimage_crash_copy_vmcoreinfo(struct kimage *image)
{
        struct page *vmcoreinfo_page;
        void *safecopy;

        if (image->type != KEXEC_TYPE_CRASH)
                return 0;

        /*
         * For kdump, allocate one vmcoreinfo safe copy from the
         * crash memory. as we have arch_kexec_protect_crashkres()
         * after kexec syscall, we naturally protect it from write
         * (even read) access under kernel direct mapping. But on
         * the other hand, we still need to operate it when crash
         * happens to generate vmcoreinfo note, hereby we rely on
         * vmap for this purpose.
         */
        vmcoreinfo_page = kimage_alloc_control_pages(image, 0);
        if (!vmcoreinfo_page) {
                pr_warn("Could not allocate vmcoreinfo buffer\n");
                return -ENOMEM;
        }
        safecopy = vmap(&vmcoreinfo_page, 1, VM_MAP, PAGE_KERNEL);
        if (!safecopy) {
                pr_warn("Could not vmap vmcoreinfo buffer\n");
                return -ENOMEM;
        }

        image->vmcoreinfo_data_copy = safecopy;
        crash_update_vmcoreinfo_safecopy(safecopy);

        return 0;
}

static int kimage_add_entry(struct kimage *image, kimage_entry_t entry)
{
        if (*image->entry != 0)
                image->entry++;

        if (image->entry == image->last_entry) {
                kimage_entry_t *ind_page;
                struct page *page;

                page = kimage_alloc_page(image, GFP_KERNEL, KIMAGE_NO_DEST);
                if (!page)
                        return -ENOMEM;

                ind_page = page_address(page);
                *image->entry = virt_to_boot_phys(ind_page) | IND_INDIRECTION;
                image->entry = ind_page;
                image->last_entry = ind_page +
                                      ((PAGE_SIZE/sizeof(kimage_entry_t)) - 1);
        }
        *image->entry = entry;
        image->entry++;
        *image->entry = 0;

        return 0;
}

static int kimage_set_destination(struct kimage *image,
                                   unsigned long destination)
{
        int result;

        destination &= PAGE_MASK;
        result = kimage_add_entry(image, destination | IND_DESTINATION);

        return result;
}


static int kimage_add_page(struct kimage *image, unsigned long page)
{
        int result;

        page &= PAGE_MASK;
        result = kimage_add_entry(image, page | IND_SOURCE);

        return result;
}


static void kimage_free_extra_pages(struct kimage *image)
{
        /* Walk through and free any extra destination pages I may have */
        kimage_free_page_list(&image->dest_pages);

        /* Walk through and free any unusable pages I have cached */
        kimage_free_page_list(&image->unusable_pages);

}
void kimage_terminate(struct kimage *image)
{
        if (*image->entry != 0)
                image->entry++;

        *image->entry = IND_DONE;
}

#define for_each_kimage_entry(image, ptr, entry) \
        for (ptr = &image->head; (entry = *ptr) && !(entry & IND_DONE); \
                ptr = (entry & IND_INDIRECTION) ? \
                        boot_phys_to_virt((entry & PAGE_MASK)) : ptr + 1)

static void kimage_free_entry(kimage_entry_t entry)
{
        struct page *page;

        page = boot_pfn_to_page(entry >> PAGE_SHIFT);
        kimage_free_pages(page);
}

void kimage_free(struct kimage *image)
{
        kimage_entry_t *ptr, entry;
        kimage_entry_t ind = 0;

        if (!image)
                return;

        if (image->vmcoreinfo_data_copy) {
                crash_update_vmcoreinfo_safecopy(NULL);
                vunmap(image->vmcoreinfo_data_copy);
        }

        kimage_free_extra_pages(image);
        for_each_kimage_entry(image, ptr, entry) {
                if (entry & IND_INDIRECTION) {
                        /* Free the previous indirection page */
                        if (ind & IND_INDIRECTION)
                                kimage_free_entry(ind);
                        /* Save this indirection page until we are
                         * done with it.
                         */
                        ind = entry;
                } else if (entry & IND_SOURCE)
                        kimage_free_entry(entry);
        }
        /* Free the final indirection page */
        if (ind & IND_INDIRECTION)
                kimage_free_entry(ind);

        /* Handle any machine specific cleanup */
        machine_kexec_cleanup(image);

        /* Free the kexec control pages... */
        kimage_free_page_list(&image->control_pages);

        /*
         * Free up any temporary buffers allocated. This might hit if
         * error occurred much later after buffer allocation.
         */
        if (image->file_mode)
                kimage_file_post_load_cleanup(image);

        kfree(image);
}

static kimage_entry_t *kimage_dst_used(struct kimage *image,
                                        unsigned long page)
{
        kimage_entry_t *ptr, entry;
        unsigned long destination = 0;

        for_each_kimage_entry(image, ptr, entry) {
                if (entry & IND_DESTINATION)
                        destination = entry & PAGE_MASK;
                else if (entry & IND_SOURCE) {
                        if (page == destination)
                                return ptr;
                        destination += PAGE_SIZE;
                }
        }

        return NULL;
}

static struct page *kimage_alloc_page(struct kimage *image,
                                        gfp_t gfp_mask,
                                        unsigned long destination)
{
        /*
         * Here we implement safeguards to ensure that a source page
         * is not copied to its destination page before the data on
         * the destination page is no longer useful.
         *
         * To do this we maintain the invariant that a source page is
         * either its own destination page, or it is not a
         * destination page at all.
         *
         * That is slightly stronger than required, but the proof
         * that no problems will not occur is trivial, and the
         * implementation is simply to verify.
         *
         * When allocating all pages normally this algorithm will run
         * in O(N) time, but in the worst case it will run in O(N^2)
         * time.   If the runtime is a problem the data structures can
         * be fixed.
         */
        struct page *page;
        unsigned long addr;

        /*
         * Walk through the list of destination pages, and see if I
         * have a match.
         */
        list_for_each_entry(page, &image->dest_pages, lru) {
                addr = page_to_boot_pfn(page) << PAGE_SHIFT;
                if (addr == destination) {
                        list_del(&page->lru);
                        return page;
                }
        }
        page = NULL;
        while (1) {
                kimage_entry_t *old;

                /* Allocate a page, if we run out of memory give up */
                page = kimage_alloc_pages(gfp_mask, 0);
                if (!page)
                        return NULL;
                /* If the page cannot be used file it away */
                if (page_to_boot_pfn(page) >
                                (KEXEC_SOURCE_MEMORY_LIMIT >> PAGE_SHIFT)) {
                        list_add(&page->lru, &image->unusable_pages);
                        continue;
                }
                addr = page_to_boot_pfn(page) << PAGE_SHIFT;

                /* If it is the destination page we want use it */
                if (addr == destination)
                        break;

                /* If the page is not a destination page use it */
                if (!kimage_is_destination_range(image, addr,
                                                  addr + PAGE_SIZE))
                        break;

                /*
                 * I know that the page is someones destination page.
                 * See if there is already a source page for this
                 * destination page.  And if so swap the source pages.
                 */
                old = kimage_dst_used(image, addr);
                if (old) {
                        /* If so move it */
                        unsigned long old_addr;
                        struct page *old_page;

                        old_addr = *old & PAGE_MASK;
                        old_page = boot_pfn_to_page(old_addr >> PAGE_SHIFT);
                        copy_highpage(page, old_page);
                        *old = addr | (*old & ~PAGE_MASK);

                        /* The old page I have found cannot be a
                         * destination page, so return it if it's
                         * gfp_flags honor the ones passed in.
                         */
                        if (!(gfp_mask & __GFP_HIGHMEM) &&
                            PageHighMem(old_page)) {
                                kimage_free_pages(old_page);
                                continue;
                        }
                        addr = old_addr;
                        page = old_page;
                        break;
                }
                /* Place the page on the destination list, to be used later */
                list_add(&page->lru, &image->dest_pages);
        }

        return page;
}

static int kimage_load_normal_segment(struct kimage *image,
                                         struct kexec_segment *segment)
{
        unsigned long maddr;
        size_t ubytes, mbytes;
        int result;
        unsigned char __user *buf = NULL;
        unsigned char *kbuf = NULL;

        result = 0;
        if (image->file_mode)
                kbuf = segment->kbuf;
        else
                buf = segment->buf;
        ubytes = segment->bufsz;
        mbytes = segment->memsz;
        maddr = segment->mem;

        result = kimage_set_destination(image, maddr);
        if (result < 0)
                goto out;

        while (mbytes) {
                struct page *page;
                char *ptr;
                size_t uchunk, mchunk;

                page = kimage_alloc_page(image, GFP_HIGHUSER, maddr);
                if (!page) {
                        result  = -ENOMEM;
                        goto out;
                }
                result = kimage_add_page(image, page_to_boot_pfn(page)
                                                                << PAGE_SHIFT);
                if (result < 0)
                        goto out;

                ptr = kmap(page);
                /* Start with a clear page */
                clear_page(ptr);
                ptr += maddr & ~PAGE_MASK;
                mchunk = min_t(size_t, mbytes,
                                PAGE_SIZE - (maddr & ~PAGE_MASK));
                uchunk = min(ubytes, mchunk);

                /* For file based kexec, source pages are in kernel memory */
                if (image->file_mode)
                        memcpy(ptr, kbuf, uchunk);
                else
                        result = copy_from_user(ptr, buf, uchunk);
                kunmap(page);
                if (result) {
                        result = -EFAULT;
                        goto out;
                }
                ubytes -= uchunk;
                maddr  += mchunk;
                if (image->file_mode)
                        kbuf += mchunk;
                else
                        buf += mchunk;
                mbytes -= mchunk;

                cond_resched();
        }
out:
        return result;
}

static int kimage_load_crash_segment(struct kimage *image,
                                        struct kexec_segment *segment)
{
        /* For crash dumps kernels we simply copy the data from
         * user space to it's destination.
         * We do things a page at a time for the sake of kmap.
         */
        unsigned long maddr;
        size_t ubytes, mbytes;
        int result;
        unsigned char __user *buf = NULL;
        unsigned char *kbuf = NULL;

        result = 0;
        if (image->file_mode)
                kbuf = segment->kbuf;
        else
                buf = segment->buf;
        ubytes = segment->bufsz;
        mbytes = segment->memsz;
        maddr = segment->mem;
        while (mbytes) {
                struct page *page;
                char *ptr;
                size_t uchunk, mchunk;

                page = boot_pfn_to_page(maddr >> PAGE_SHIFT);
                if (!page) {
                        result  = -ENOMEM;
                        goto out;
                }
                ptr = kmap(page);
                ptr += maddr & ~PAGE_MASK;
                mchunk = min_t(size_t, mbytes,
                                PAGE_SIZE - (maddr & ~PAGE_MASK));
                uchunk = min(ubytes, mchunk);
                if (mchunk > uchunk) {
                        /* Zero the trailing part of the page */
                        memset(ptr + uchunk, 0, mchunk - uchunk);
                }

                /* For file based kexec, source pages are in kernel memory */
                if (image->file_mode)
                        memcpy(ptr, kbuf, uchunk);
                else
                        result = copy_from_user(ptr, buf, uchunk);
                kexec_flush_icache_page(page);
                kunmap(page);
                if (result) {
                        result = -EFAULT;
                        goto out;
                }
                ubytes -= uchunk;
                maddr  += mchunk;
                if (image->file_mode)
                        kbuf += mchunk;
                else
                        buf += mchunk;
                mbytes -= mchunk;

                cond_resched();
        }
out:
        return result;
}

int kimage_load_segment(struct kimage *image,
                                struct kexec_segment *segment)
{
        int result = -ENOMEM;

        switch (image->type) {
        case KEXEC_TYPE_DEFAULT:
                result = kimage_load_normal_segment(image, segment);
                break;
        case KEXEC_TYPE_CRASH:
                result = kimage_load_crash_segment(image, segment);
                break;
        }

        return result;
}

struct kimage *kexec_image;
struct kimage *kexec_crash_image;
int kexec_load_disabled;

/*
 * No panic_cpu check version of crash_kexec().  This function is called
 * only when panic_cpu holds the current CPU number; this is the only CPU
 * which processes crash_kexec routines.
 */
void __noclone __crash_kexec(struct pt_regs *regs)
{
        /* Take the kexec_mutex here to prevent sys_kexec_load
         * running on one cpu from replacing the crash kernel
         * we are using after a panic on a different cpu.
         *
         * If the crash kernel was not located in a fixed area
         * of memory the xchg(&kexec_crash_image) would be
         * sufficient.  But since I reuse the memory...
         */
        if (mutex_trylock(&kexec_mutex)) {
                if (kexec_crash_image) {
                        struct pt_regs fixed_regs;

                        crash_setup_regs(&fixed_regs, regs);
                        crash_save_vmcoreinfo();
                        machine_crash_shutdown(&fixed_regs);
                        machine_kexec(kexec_crash_image);
                }
                mutex_unlock(&kexec_mutex);
        }
}
STACK_FRAME_NON_STANDARD(__crash_kexec);

void crash_kexec(struct pt_regs *regs)
{
        int old_cpu, this_cpu;

        /*
         * Only one CPU is allowed to execute the crash_kexec() code as with
         * panic().  Otherwise parallel calls of panic() and crash_kexec()
         * may stop each other.  To exclude them, we use panic_cpu here too.
         */
        this_cpu = raw_smp_processor_id();
        old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu);
        if (old_cpu == PANIC_CPU_INVALID) {
                /* This is the 1st CPU which comes here, so go ahead. */
                printk_safe_flush_on_panic();
                __crash_kexec(regs);

                /*
                 * Reset panic_cpu to allow another panic()/crash_kexec()
                 * call.
                 */
                atomic_set(&panic_cpu, PANIC_CPU_INVALID);
        }
}

size_t crash_get_memory_size(void)
{
        size_t size = 0;

        mutex_lock(&kexec_mutex);
        if (crashk_res.end != crashk_res.start)
                size = resource_size(&crashk_res);
        mutex_unlock(&kexec_mutex);
        return size;
}

void __weak crash_free_reserved_phys_range(unsigned long begin,
                                           unsigned long end)
{
        unsigned long addr;

        for (addr = begin; addr < end; addr += PAGE_SIZE)
                free_reserved_page(boot_pfn_to_page(addr >> PAGE_SHIFT));
}

int crash_shrink_memory(unsigned long new_size)
{

        int ret = 0;
        unsigned long start, end;
        unsigned long old_size;
        struct resource *ram_res;

        mutex_lock(&kexec_mutex);

        if (kexec_crash_image) {
                ret = -ENOENT;
                goto unlock;
        }
        start = crashk_res.start;
        end = crashk_res.end;
        old_size = (end == 0) ? 0 : end - start + 1;
        if (new_size >= old_size) {
                ret = (new_size == old_size) ? 0 : -EINVAL;
                goto unlock;
        }

        ram_res = kzalloc(sizeof(*ram_res), GFP_KERNEL);
        if (!ram_res) {
                ret = -ENOMEM;
                goto unlock;
        }

        start = roundup(start, KEXEC_CRASH_MEM_ALIGN);
        end = roundup(start + new_size, KEXEC_CRASH_MEM_ALIGN);

        crash_free_reserved_phys_range(end, crashk_res.end);

        if ((start == end) && (crashk_res.parent != NULL))
                release_resource(&crashk_res);

        ram_res->start = end;
        ram_res->end = crashk_res.end;
        ram_res->flags = IORESOURCE_BUSY | IORESOURCE_SYSTEM_RAM;
        ram_res->name = "System RAM";

        crashk_res.end = end - 1;

        insert_resource(&iomem_resource, ram_res);

unlock:
        mutex_unlock(&kexec_mutex);
        return ret;
}

void crash_save_cpu(struct pt_regs *regs, int cpu)
{
        struct elf_prstatus prstatus;
        u32 *buf;

        if ((cpu < 0) || (cpu >= nr_cpu_ids))
                return;

        /* Using ELF notes here is opportunistic.
         * I need a well defined structure format
         * for the data I pass, and I need tags
         * on the data to indicate what information I have
         * squirrelled away.  ELF notes happen to provide
         * all of that, so there is no need to invent something new.
         */
        buf = (u32 *)per_cpu_ptr(crash_notes, cpu);
        if (!buf)
                return;
        memset(&prstatus, 0, sizeof(prstatus));
        prstatus.pr_pid = current->pid;
        elf_core_copy_kernel_regs(&prstatus.pr_reg, regs);
        buf = append_elf_note(buf, KEXEC_CORE_NOTE_NAME, NT_PRSTATUS,
                              &prstatus, sizeof(prstatus));
        final_note(buf);
}

static int __init crash_notes_memory_init(void)
{
        /* Allocate memory for saving cpu registers. */
        size_t size, align;

        /*
         * crash_notes could be allocated across 2 vmalloc pages when percpu
         * is vmalloc based . vmalloc doesn't guarantee 2 continuous vmalloc
         * pages are also on 2 continuous physical pages. In this case the
         * 2nd part of crash_notes in 2nd page could be lost since only the
         * starting address and size of crash_notes are exported through sysfs.
         * Here round up the size of crash_notes to the nearest power of two
         * and pass it to __alloc_percpu as align value. This can make sure
         * crash_notes is allocated inside one physical page.
         */
        size = sizeof(note_buf_t);
        align = min(roundup_pow_of_two(sizeof(note_buf_t)), PAGE_SIZE);

        /*
         * Break compile if size is bigger than PAGE_SIZE since crash_notes
         * definitely will be in 2 pages with that.
         */
        BUILD_BUG_ON(size > PAGE_SIZE);

        crash_notes = __alloc_percpu(size, align);
        if (!crash_notes) {
                pr_warn("Memory allocation for saving cpu register states failed\n");
                return -ENOMEM;
        }
        return 0;
}
subsys_initcall(crash_notes_memory_init);


/*
 * Move into place and start executing a preloaded standalone
 * executable.  If nothing was preloaded return an error.
 */
int kernel_kexec(void)
{
        int error = 0;

        if (!mutex_trylock(&kexec_mutex))
                return -EBUSY;
        if (!kexec_image) {
                error = -EINVAL;
                goto Unlock;
        }

#ifdef CONFIG_KEXEC_JUMP
        if (kexec_image->preserve_context) {
                lock_system_sleep();
                pm_prepare_console();
                error = freeze_processes();
                if (error) {
                        error = -EBUSY;
                        goto Restore_console;
                }
                suspend_console();
                error = dpm_suspend_start(PMSG_FREEZE);
                if (error)
                        goto Resume_console;
                /* At this point, dpm_suspend_start() has been called,
                 * but *not* dpm_suspend_end(). We *must* call
                 * dpm_suspend_end() now.  Otherwise, drivers for
                 * some devices (e.g. interrupt controllers) become
                 * desynchronized with the actual state of the
                 * hardware at resume time, and evil weirdness ensues.
                 */
                error = dpm_suspend_end(PMSG_FREEZE);
                if (error)
                        goto Resume_devices;
                error = disable_nonboot_cpus();
                if (error)
                        goto Enable_cpus;
                local_irq_disable();
                error = syscore_suspend();
                if (error)
                        goto Enable_irqs;
        } else
#endif
        {
                kexec_in_progress = true;
                kernel_restart_prepare(NULL);
                migrate_to_reboot_cpu();

                /*
                 * migrate_to_reboot_cpu() disables CPU hotplug assuming that
                 * no further code needs to use CPU hotplug (which is true in
                 * the reboot case). However, the kexec path depends on using
                 * CPU hotplug again; so re-enable it here.
                 */
                cpu_hotplug_enable();
                pr_emerg("Starting new kernel\n");
                machine_shutdown();
        }

        machine_kexec(kexec_image);

#ifdef CONFIG_KEXEC_JUMP
        if (kexec_image->preserve_context) {
                syscore_resume();
 Enable_irqs:
                local_irq_enable();
 Enable_cpus:
                enable_nonboot_cpus();
                dpm_resume_start(PMSG_RESTORE);
 Resume_devices:
                dpm_resume_end(PMSG_RESTORE);
 Resume_console:
                resume_console();
                thaw_processes();
 Restore_console:
                pm_restore_console();
                unlock_system_sleep();
        }
#endif

 Unlock:
        mutex_unlock(&kexec_mutex);
        return error;
}

/*
 * Protection mechanism for crashkernel reserved memory after
 * the kdump kernel is loaded.
 *
 * Provide an empty default implementation here -- architecture
 * code may override this
 */
void __weak arch_kexec_protect_crashkres(void)
{}

void __weak arch_kexec_unprotect_crashkres(void)
{}