/*
   * kexec.c - kexec system call
   * 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.
   */

  #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/spinlock.h>
  #include <linux/list.h>
  #include <linux/highmem.h>
  #include <linux/syscalls.h>
  #include <linux/reboot.h>
  #include <linux/syscalls.h>
  #include <linux/ioport.h>

  #include <linux/hardirq.h>

  #include <asm/page.h>
  #include <asm/uaccess.h>
  #include <asm/io.h>
  #include <asm/system.h>
  #include <asm/semaphore.h>

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

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

  int kexec_should_crash(struct task_struct *p)
  {
  	if (in_interrupt() || !p->pid || p->pid == 1 || panic_on_oops)
  		return 1;
  	return 0;
  }

  /*
   * 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_CODE_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)

  static int kimage_is_destination_range(struct kimage *image,
  				       unsigned long start, unsigned long end);
  static struct page *kimage_alloc_page(struct kimage *image,

  				       gfp_t gfp_mask,

  				       unsigned long dest);

  
  static int do_kimage_alloc(struct kimage **rimage, unsigned long entry,

  	                    unsigned long nr_segments,
                              struct kexec_segment __user *segments)

  {
  	size_t segment_bytes;
  	struct kimage *image;
  	unsigned long i;
  	int result;
  
  	/* Allocate a controlling structure */
  	result = -ENOMEM;
  	image = kmalloc(sizeof(*image), GFP_KERNEL);

  	if (!image)

  		goto out;

  	memset(image, 0, sizeof(*image));
  	image->head = 0;
  	image->entry = &image->head;
  	image->last_entry = &image->head;
  	image->control_page = ~0; /* By default this does not apply */
  	image->start = entry;
  	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 unuseable pages */
  	INIT_LIST_HEAD(&image->unuseable_pages);
  
  	/* Read in the segments */
  	image->nr_segments = nr_segments;
  	segment_bytes = nr_segments * sizeof(*segments);
  	result = copy_from_user(image->segment, segments, segment_bytes);
  	if (result)
  		goto out;
  
  	/*
  	 * 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 addreses 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.
  	 */
  	result = -EADDRNOTAVAIL;
  	for (i = 0; i < nr_segments; i++) {
  		unsigned long mstart, mend;

  		mstart = image->segment[i].mem;
  		mend   = mstart + image->segment[i].memsz;
  		if ((mstart & ~PAGE_MASK) || (mend & ~PAGE_MASK))
  			goto out;
  		if (mend >= KEXEC_DESTINATION_MEMORY_LIMIT)
  			goto out;
  	}
  
  	/* 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.
  	 */
  	result = -EINVAL;

  	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))
  				goto out;
  		}
  	}
  
  	/* 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.
  	 */
  	result = -EINVAL;

  	for (i = 0; i < nr_segments; i++) {

  		if (image->segment[i].bufsz > image->segment[i].memsz)
  			goto out;
  	}

  	result = 0;

  out:
  	if (result == 0)

  		*rimage = image;

  	else

  		kfree(image);

  	return result;
  
  }
  
  static int kimage_normal_alloc(struct kimage **rimage, unsigned long entry,

  				unsigned long nr_segments,
  				struct kexec_segment __user *segments)

  {
  	int result;
  	struct kimage *image;
  
  	/* Allocate and initialize a controlling structure */
  	image = NULL;
  	result = do_kimage_alloc(&image, entry, nr_segments, segments);

  	if (result)

  		goto out;

  	*rimage = image;
  
  	/*
  	 * Find a location for the control code buffer, and add it
  	 * the vector of segments so that it's pages will also be
  	 * counted as destination pages.
  	 */
  	result = -ENOMEM;
  	image->control_code_page = kimage_alloc_control_pages(image,

  					   get_order(KEXEC_CONTROL_CODE_SIZE));

  	if (!image->control_code_page) {
  		printk(KERN_ERR "Could not allocate control_code_buffer
  ");
  		goto out;
  	}
  
  	result = 0;
   out:

  	if (result == 0)

  		*rimage = image;

  	else

  		kfree(image);

  	return result;
  }
  
  static int kimage_crash_alloc(struct kimage **rimage, unsigned long entry,

  				unsigned long nr_segments,

  				struct kexec_segment __user *segments)

  {
  	int result;
  	struct kimage *image;
  	unsigned long i;
  
  	image = NULL;
  	/* Verify we have a valid entry point */
  	if ((entry < crashk_res.start) || (entry > crashk_res.end)) {
  		result = -EADDRNOTAVAIL;
  		goto out;
  	}
  
  	/* Allocate and initialize a controlling structure */
  	result = do_kimage_alloc(&image, entry, nr_segments, segments);

  	if (result)

  		goto out;

  
  	/* Enable the special crash kernel control page
  	 * allocation policy.
  	 */
  	image->control_page = crashk_res.start;
  	image->type = KEXEC_TYPE_CRASH;
  
  	/*
  	 * 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.
  	 */
  	result = -EADDRNOTAVAIL;
  	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 < crashk_res.start) || (mend > crashk_res.end))
  			goto out;
  	}

  	/*
  	 * Find a location for the control code buffer, and add
  	 * the vector of segments so that it's pages will also be
  	 * counted as destination pages.
  	 */
  	result = -ENOMEM;
  	image->control_code_page = kimage_alloc_control_pages(image,

  					   get_order(KEXEC_CONTROL_CODE_SIZE));

  	if (!image->control_code_page) {
  		printk(KERN_ERR "Could not allocate control_code_buffer
  ");
  		goto out;
  	}
  
  	result = 0;

  out:
  	if (result == 0)

  		*rimage = image;

  	else

  		kfree(image);

  	return result;
  }

  static 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, 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);

  	}

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

  	order = page_private(page);

  	count = 1 << order;

  	for (i = 0; i < count; i++)

  		ClearPageReserved(page + i);

  	__free_pages(page, order);
  }
  
  static void kimage_free_page_list(struct list_head *list)
  {
  	struct list_head *pos, *next;

  	list_for_each_safe(pos, next, list) {
  		struct page *page;
  
  		page = list_entry(pos, struct page, 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(GFP_KERNEL, order);
  		if (!pages)
  			break;
  		pfn   = page_to_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 everyting 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;

  
  		if (hole_end > KEXEC_CONTROL_MEMORY_LIMIT)

  			break;

  		if (hole_end > crashk_res.end)

  			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);
  			break;
  		}
  	}

  	if (pages)

  		image->control_page = hole_end;

  	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;
  }
  
  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_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);

  	if (result == 0)

  		image->destination = 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);

  	if (result == 0)

  		image->destination += PAGE_SIZE;

  	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 unuseable pages I have cached */
  	kimage_free_page_list(&image->unuseable_pages);
  
  }
  static int kimage_terminate(struct kimage *image)
  {

  	if (*image->entry != 0)

  		image->entry++;

  	*image->entry = IND_DONE;

  	return 0;
  }
  
  #define for_each_kimage_entry(image, ptr, entry) \
  	for (ptr = &image->head; (entry = *ptr) && !(entry & IND_DONE); \
  		ptr = (entry & IND_INDIRECTION)? \
  			phys_to_virt((entry & PAGE_MASK)): ptr +1)
  
  static void kimage_free_entry(kimage_entry_t entry)
  {
  	struct page *page;
  
  	page = pfn_to_page(entry >> PAGE_SHIFT);
  	kimage_free_pages(page);
  }
  
  static void kimage_free(struct kimage *image)
  {
  	kimage_entry_t *ptr, entry;
  	kimage_entry_t ind = 0;
  
  	if (!image)
  		return;

  	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);
  	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_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_pfn(page) >
  				(KEXEC_SOURCE_MEMORY_LIMIT >> PAGE_SHIFT)) {

  			list_add(&page->lru, &image->unuseable_pages);
  			continue;
  		}
  		addr = page_to_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 = 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.
  			 */
  			addr = old_addr;
  			page = old_page;
  			break;
  		}
  		else {
  			/* Place the page on the destination list I
  			 * will use it 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;
  	unsigned long ubytes, mbytes;
  	int result;

  	unsigned char __user *buf;

  
  	result = 0;
  	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 == 0) {
  			result  = -ENOMEM;
  			goto out;
  		}

  		result = kimage_add_page(image, page_to_pfn(page)
  								<< PAGE_SHIFT);
  		if (result < 0)

  			goto out;

  		ptr = kmap(page);
  		/* Start with a clear page */
  		memset(ptr, 0, PAGE_SIZE);
  		ptr += maddr & ~PAGE_MASK;
  		mchunk = PAGE_SIZE - (maddr & ~PAGE_MASK);

  		if (mchunk > mbytes)

  			mchunk = mbytes;

  		uchunk = mchunk;

  		if (uchunk > ubytes)

  			uchunk = ubytes;

  		result = copy_from_user(ptr, buf, uchunk);
  		kunmap(page);
  		if (result) {
  			result = (result < 0) ? result : -EIO;
  			goto out;
  		}
  		ubytes -= uchunk;
  		maddr  += mchunk;
  		buf    += mchunk;
  		mbytes -= mchunk;
  	}

  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;
  	unsigned long ubytes, mbytes;
  	int result;

  	unsigned char __user *buf;

  
  	result = 0;
  	buf = segment->buf;
  	ubytes = segment->bufsz;
  	mbytes = segment->memsz;
  	maddr = segment->mem;

  	while (mbytes) {

  		struct page *page;
  		char *ptr;
  		size_t uchunk, mchunk;

  		page = pfn_to_page(maddr >> PAGE_SHIFT);
  		if (page == 0) {
  			result  = -ENOMEM;
  			goto out;
  		}
  		ptr = kmap(page);
  		ptr += maddr & ~PAGE_MASK;
  		mchunk = PAGE_SIZE - (maddr & ~PAGE_MASK);

  		if (mchunk > mbytes)

  			mchunk = mbytes;

  		uchunk = mchunk;
  		if (uchunk > ubytes) {
  			uchunk = ubytes;
  			/* Zero the trailing part of the page */
  			memset(ptr + uchunk, 0, mchunk - uchunk);
  		}
  		result = copy_from_user(ptr, buf, uchunk);
  		kunmap(page);
  		if (result) {
  			result = (result < 0) ? result : -EIO;
  			goto out;
  		}
  		ubytes -= uchunk;
  		maddr  += mchunk;
  		buf    += mchunk;
  		mbytes -= mchunk;
  	}

  out:

  	return result;
  }
  
  static 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;
  }
  
  /*
   * Exec Kernel system call: for obvious reasons only root may call it.
   *
   * This call breaks up into three pieces.
   * - A generic part which loads the new kernel from the current
   *   address space, and very carefully places the data in the
   *   allocated pages.
   *
   * - A generic part that interacts with the kernel and tells all of
   *   the devices to shut down.  Preventing on-going dmas, and placing
   *   the devices in a consistent state so a later kernel can
   *   reinitialize them.
   *
   * - A machine specific part that includes the syscall number
   *   and the copies the image to it's final destination.  And
   *   jumps into the image at entry.
   *
   * kexec does not sync, or unmount filesystems so if you need
   * that to happen you need to do that yourself.
   */

  struct kimage *kexec_image;
  struct kimage *kexec_crash_image;

  /*
   * A home grown binary mutex.
   * Nothing can wait so this mutex is safe to use
   * in interrupt context :)
   */

  static int kexec_lock;

  asmlinkage long sys_kexec_load(unsigned long entry, unsigned long nr_segments,
  				struct kexec_segment __user *segments,
  				unsigned long flags)

  {
  	struct kimage **dest_image, *image;
  	int locked;
  	int result;
  
  	/* We only trust the superuser with rebooting the system. */
  	if (!capable(CAP_SYS_BOOT))
  		return -EPERM;
  
  	/*
  	 * Verify we have a legal set of flags
  	 * This leaves us room for future extensions.
  	 */
  	if ((flags & KEXEC_FLAGS) != (flags & ~KEXEC_ARCH_MASK))
  		return -EINVAL;
  
  	/* Verify we are on the appropriate architecture */
  	if (((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH) &&
  		((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT))

  		return -EINVAL;

  
  	/* Put an artificial cap on the number
  	 * of segments passed to kexec_load.
  	 */
  	if (nr_segments > KEXEC_SEGMENT_MAX)
  		return -EINVAL;
  
  	image = NULL;
  	result = 0;
  
  	/* Because we write directly to the reserved memory
  	 * region when loading crash kernels we need a mutex here to
  	 * prevent multiple crash  kernels from attempting to load
  	 * simultaneously, and to prevent a crash kernel from loading
  	 * over the top of a in use crash kernel.
  	 *
  	 * KISS: always take the mutex.
  	 */
  	locked = xchg(&kexec_lock, 1);

  	if (locked)

  		return -EBUSY;

  	dest_image = &kexec_image;

  	if (flags & KEXEC_ON_CRASH)

  		dest_image = &kexec_crash_image;

  	if (nr_segments > 0) {
  		unsigned long i;

  		/* Loading another kernel to reboot into */

  		if ((flags & KEXEC_ON_CRASH) == 0)
  			result = kimage_normal_alloc(&image, entry,
  							nr_segments, segments);

  		/* Loading another kernel to switch to if this one crashes */
  		else if (flags & KEXEC_ON_CRASH) {
  			/* Free any current crash dump kernel before
  			 * we corrupt it.
  			 */
  			kimage_free(xchg(&kexec_crash_image, NULL));

  			result = kimage_crash_alloc(&image, entry,
  						     nr_segments, segments);

  		}

  		if (result)

  			goto out;

  		result = machine_kexec_prepare(image);

  		if (result)

  			goto out;

  
  		for (i = 0; i < nr_segments; i++) {

  			result = kimage_load_segment(image, &image->segment[i]);

  			if (result)

  				goto out;

  		}
  		result = kimage_terminate(image);

  		if (result)

  			goto out;

  	}
  	/* Install the new kernel, and  Uninstall the old */
  	image = xchg(dest_image, image);

  out:

  	xchg(&kexec_lock, 0); /* Release the mutex */
  	kimage_free(image);

  	return result;
  }
  
  #ifdef CONFIG_COMPAT
  asmlinkage long compat_sys_kexec_load(unsigned long entry,

  				unsigned long nr_segments,
  				struct compat_kexec_segment __user *segments,
  				unsigned long flags)

  {
  	struct compat_kexec_segment in;
  	struct kexec_segment out, __user *ksegments;
  	unsigned long i, result;
  
  	/* Don't allow clients that don't understand the native
  	 * architecture to do anything.
  	 */

  	if ((flags & KEXEC_ARCH_MASK) == KEXEC_ARCH_DEFAULT)

  		return -EINVAL;

  	if (nr_segments > KEXEC_SEGMENT_MAX)

  		return -EINVAL;

  
  	ksegments = compat_alloc_user_space(nr_segments * sizeof(out));
  	for (i=0; i < nr_segments; i++) {
  		result = copy_from_user(&in, &segments[i], sizeof(in));

  		if (result)

  			return -EFAULT;

  
  		out.buf   = compat_ptr(in.buf);
  		out.bufsz = in.bufsz;
  		out.mem   = in.mem;
  		out.memsz = in.memsz;
  
  		result = copy_to_user(&ksegments[i], &out, sizeof(out));

  		if (result)

  			return -EFAULT;

  	}
  
  	return sys_kexec_load(entry, nr_segments, ksegments, flags);
  }
  #endif

  void crash_kexec(struct pt_regs *regs)

  {

  	int locked;
  
  
  	/* Take the kexec_lock 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...
  	 */
  	locked = xchg(&kexec_lock, 1);
  	if (!locked) {

  		if (kexec_crash_image) {

  			struct pt_regs fixed_regs;
  			crash_setup_regs(&fixed_regs, regs);
  			machine_crash_shutdown(&fixed_regs);

  			machine_kexec(kexec_crash_image);

  		}
  		xchg(&kexec_lock, 0);
  	}
  }

  
  static int __init crash_notes_memory_init(void)
  {
  	/* Allocate memory for saving cpu registers. */
  	crash_notes = alloc_percpu(note_buf_t);
  	if (!crash_notes) {
  		printk("Kexec: Memory allocation for saving cpu register"
  		" states failed
  ");
  		return -ENOMEM;
  	}
  	return 0;
  }
  module_init(crash_notes_memory_init)