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 *    Memory preserving reboot related code.
 *    Created by: Hariprasad Nellitheertha (hari@in.ibm.com)
 *    Copyright (C) IBM Corporation, 2004. All rights reserved

#include <linux/errno.h>
#include <linux/highmem.h>
#include <linux/crash_dump.h>

#include <asm/uaccess.h>

static void *kdump_buf_page;

 * copy_oldmem_page - copy one page from "oldmem"
 * @pfn: page frame number to be copied
 * @buf: target memory address for the copy; this can be in kernel address
 *    space or user address space (see @userbuf)
 * @csize: number of bytes to copy
 * @offset: offset in bytes into the page (based on pfn) to begin the copy
 * @userbuf: if set, @buf is in user address space, use copy_to_user(),
 *    otherwise @buf is in kernel address space, use memcpy().
 * Copy a page from "oldmem". For this page, there is no pte mapped
 * in the current kernel. We stitch up a pte, similar to kmap_atomic.
 * Calling copy_to_user() in atomic context is not desirable. Hence first
 * copying the data to a pre-allocated kernel page and then copying to user
 * space in non-atomic context.
ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
                               size_t csize, unsigned long offset, int userbuf)
      void  *vaddr;

      if (!csize)
            return 0;

      vaddr = kmap_atomic_pfn(pfn, KM_PTE0);

      if (!userbuf) {
            memcpy(buf, (vaddr + offset), csize);
            kunmap_atomic(vaddr, KM_PTE0);
      } else {
            if (!kdump_buf_page) {
                  printk(KERN_WARNING "Kdump: Kdump buffer page not"
                        " allocated\n");
                  kunmap_atomic(vaddr, KM_PTE0);
                  return -EFAULT;
            copy_page(kdump_buf_page, vaddr);
            kunmap_atomic(vaddr, KM_PTE0);
            if (copy_to_user(buf, (kdump_buf_page + offset), csize))
                  return -EFAULT;

      return csize;

static int __init kdump_buf_page_init(void)
      int ret = 0;

      kdump_buf_page = kmalloc(PAGE_SIZE, GFP_KERNEL);
      if (!kdump_buf_page) {
            printk(KERN_WARNING "Kdump: Failed to allocate kdump buffer"
                   " page\n");
            ret = -ENOMEM;

      return ret;

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