text: /*
   *	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;
  
  /* Stores the physical address of elf header of crash image. */
  unsigned long long elfcorehdr_addr = ELFCORE_ADDR_MAX;
  
  static inline bool is_crashed_pfn_valid(unsigned long pfn)
  {
  #ifndef CONFIG_X86_PAE
  	/*
  	 * non-PAE kdump kernel executed from a PAE one will crop high pte
  	 * bits and poke unwanted space counting again from address 0, we
  	 * don't want that. pte must fit into unsigned long. In fact the
  	 * test checks high 12 bits for being zero (pfn will be shifted left
  	 * by PAGE_SHIFT).
  	 */
  	return pte_pfn(pfn_pte(pfn, __pgprot(0))) == pfn;
  #else
  	return true;
  #endif
  }
  
  /**
   * 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;
  
  	if (!is_crashed_pfn_valid(pfn))
  		return -EFAULT;
  
  	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;
  }
  arch_initcall(kdump_buf_page_init);
  