/******************************************************************************

   * Xen balloon driver - enables returning/claiming memory to/from Xen.
   *
   * Copyright (c) 2003, B Dragovic
   * Copyright (c) 2003-2004, M Williamson, K Fraser
   * Copyright (c) 2005 Dan M. Smith, IBM Corporation
   *
   * 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; or, when distributed
   * separately from the Linux kernel or incorporated into other
   * software packages, subject to the following license:
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this source file (the "Software"), to deal in the Software without
   * restriction, including without limitation the rights to use, copy, modify,
   * merge, publish, distribute, sublicense, and/or sell copies of the Software,
   * and to permit persons to whom the Software is furnished to do so, subject to
   * the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
   * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
   * IN THE SOFTWARE.
   */
  
  #include <linux/kernel.h>

  #include <linux/sched.h>
  #include <linux/errno.h>
  #include <linux/mm.h>
  #include <linux/bootmem.h>
  #include <linux/pagemap.h>
  #include <linux/highmem.h>
  #include <linux/mutex.h>

  #include <linux/list.h>

  #include <linux/gfp.h>

  #include <asm/page.h>
  #include <asm/pgalloc.h>
  #include <asm/pgtable.h>

  #include <asm/tlb.h>

  #include <asm/e820.h>

  #include <asm/xen/hypervisor.h>
  #include <asm/xen/hypercall.h>

  
  #include <xen/xen.h>

  #include <xen/interface/xen.h>

  #include <xen/interface/memory.h>

  #include <xen/balloon.h>

  #include <xen/features.h>
  #include <xen/page.h>

  /*
   * balloon_process() state:
   *
   * BP_DONE: done or nothing to do,
   * BP_EAGAIN: error, go to sleep,
   * BP_ECANCELED: error, balloon operation canceled.
   */

  enum bp_state {
  	BP_DONE,
  	BP_EAGAIN,
  	BP_ECANCELED

  };

  static DEFINE_MUTEX(balloon_mutex);

  struct balloon_stats balloon_stats;
  EXPORT_SYMBOL_GPL(balloon_stats);

  
  /* We increase/decrease in batches which fit in a page */
  static unsigned long frame_list[PAGE_SIZE / sizeof(unsigned long)];

  #ifdef CONFIG_HIGHMEM

  #define inc_totalhigh_pages() (totalhigh_pages++)
  #define dec_totalhigh_pages() (totalhigh_pages--)
  #else
  #define inc_totalhigh_pages() do {} while(0)
  #define dec_totalhigh_pages() do {} while(0)
  #endif
  
  /* List of ballooned pages, threaded through the mem_map array. */
  static LIST_HEAD(ballooned_pages);
  
  /* Main work function, always executed in process context. */
  static void balloon_process(struct work_struct *work);

  static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);

  
  /* When ballooning out (allocating memory to return to Xen) we don't really
     want the kernel to try too hard since that can trigger the oom killer. */
  #define GFP_BALLOON \
  	(GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
  
  static void scrub_page(struct page *page)
  {
  #ifdef CONFIG_XEN_SCRUB_PAGES

  	clear_highpage(page);

  #endif
  }
  
  /* balloon_append: add the given page to the balloon. */

  static void __balloon_append(struct page *page)

  {
  	/* Lowmem is re-populated first, so highmem pages go at list tail. */
  	if (PageHighMem(page)) {
  		list_add_tail(&page->lru, &ballooned_pages);
  		balloon_stats.balloon_high++;

  	} else {
  		list_add(&page->lru, &ballooned_pages);
  		balloon_stats.balloon_low++;
  	}

  }

  static void balloon_append(struct page *page)
  {
  	__balloon_append(page);

  	if (PageHighMem(page))
  		dec_totalhigh_pages();

  	totalram_pages--;

  }
  
  /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */

  static struct page *balloon_retrieve(bool prefer_highmem)

  {
  	struct page *page;
  
  	if (list_empty(&ballooned_pages))
  		return NULL;

  	if (prefer_highmem)
  		page = list_entry(ballooned_pages.prev, struct page, lru);
  	else
  		page = list_entry(ballooned_pages.next, struct page, lru);

  	list_del(&page->lru);
  
  	if (PageHighMem(page)) {
  		balloon_stats.balloon_high--;
  		inc_totalhigh_pages();
  	}
  	else
  		balloon_stats.balloon_low--;

  	totalram_pages++;

  	return page;
  }
  
  static struct page *balloon_first_page(void)
  {
  	if (list_empty(&ballooned_pages))
  		return NULL;
  	return list_entry(ballooned_pages.next, struct page, lru);
  }
  
  static struct page *balloon_next_page(struct page *page)
  {
  	struct list_head *next = page->lru.next;
  	if (next == &ballooned_pages)
  		return NULL;
  	return list_entry(next, struct page, lru);
  }

  static enum bp_state update_schedule(enum bp_state state)

  {

  	if (state == BP_DONE) {
  		balloon_stats.schedule_delay = 1;
  		balloon_stats.retry_count = 1;
  		return BP_DONE;
  	}

  	++balloon_stats.retry_count;
  
  	if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&
  			balloon_stats.retry_count > balloon_stats.max_retry_count) {

  		balloon_stats.schedule_delay = 1;
  		balloon_stats.retry_count = 1;
  		return BP_ECANCELED;
  	}
  
  	balloon_stats.schedule_delay <<= 1;
  
  	if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)
  		balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
  
  	return BP_EAGAIN;

  }

  static long current_credit(void)

  {

  	unsigned long target = balloon_stats.target_pages;

  
  	target = min(target,
  		     balloon_stats.current_pages +
  		     balloon_stats.balloon_low +
  		     balloon_stats.balloon_high);

  	return target - balloon_stats.current_pages;

  }

  static enum bp_state increase_reservation(unsigned long nr_pages)

  {

  	int rc;

  	unsigned long  pfn, i;

  	struct page   *page;

  	struct xen_memory_reservation reservation = {
  		.address_bits = 0,
  		.extent_order = 0,
  		.domid        = DOMID_SELF
  	};
  
  	if (nr_pages > ARRAY_SIZE(frame_list))
  		nr_pages = ARRAY_SIZE(frame_list);

  	page = balloon_first_page();
  	for (i = 0; i < nr_pages; i++) {

  		if (!page) {
  			nr_pages = i;
  			break;
  		}

  		frame_list[i] = page_to_pfn(page);

  		page = balloon_next_page(page);
  	}

  	set_xen_guest_handle(reservation.extent_start, frame_list);

  	reservation.nr_extents = nr_pages;
  	rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);

  	if (rc <= 0)

  		return BP_EAGAIN;

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

  		page = balloon_retrieve(false);

  		BUG_ON(page == NULL);
  
  		pfn = page_to_pfn(page);
  		BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
  		       phys_to_machine_mapping_valid(pfn));
  
  		set_phys_to_machine(pfn, frame_list[i]);
  
  		/* Link back into the page tables if not highmem. */

  		if (xen_pv_domain() && !PageHighMem(page)) {

  			int ret;
  			ret = HYPERVISOR_update_va_mapping(
  				(unsigned long)__va(pfn << PAGE_SHIFT),
  				mfn_pte(frame_list[i], PAGE_KERNEL),
  				0);
  			BUG_ON(ret);
  		}
  
  		/* Relinquish the page back to the allocator. */
  		ClearPageReserved(page);
  		init_page_count(page);
  		__free_page(page);
  	}

  	balloon_stats.current_pages += rc;

  	return BP_DONE;

  }

  static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)

  {

  	enum bp_state state = BP_DONE;

  	unsigned long  pfn, i;

  	struct page   *page;

  	int ret;
  	struct xen_memory_reservation reservation = {
  		.address_bits = 0,
  		.extent_order = 0,
  		.domid        = DOMID_SELF
  	};
  
  	if (nr_pages > ARRAY_SIZE(frame_list))
  		nr_pages = ARRAY_SIZE(frame_list);
  
  	for (i = 0; i < nr_pages; i++) {

  		if ((page = alloc_page(gfp)) == NULL) {

  			nr_pages = i;

  			state = BP_EAGAIN;

  			break;
  		}
  
  		pfn = page_to_pfn(page);
  		frame_list[i] = pfn_to_mfn(pfn);
  
  		scrub_page(page);

  		if (xen_pv_domain() && !PageHighMem(page)) {

  			ret = HYPERVISOR_update_va_mapping(
  				(unsigned long)__va(pfn << PAGE_SHIFT),
  				__pte_ma(0), 0);
  			BUG_ON(ret);
                  }

  	}
  
  	/* Ensure that ballooned highmem pages don't have kmaps. */
  	kmap_flush_unused();
  	flush_tlb_all();

  	/* No more mappings: invalidate P2M and add to balloon. */
  	for (i = 0; i < nr_pages; i++) {
  		pfn = mfn_to_pfn(frame_list[i]);

  		__set_phys_to_machine(pfn, INVALID_P2M_ENTRY);

  		balloon_append(pfn_to_page(pfn));
  	}

  	set_xen_guest_handle(reservation.extent_start, frame_list);

  	reservation.nr_extents   = nr_pages;
  	ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
  	BUG_ON(ret != nr_pages);
  
  	balloon_stats.current_pages -= nr_pages;

  	return state;

  }
  
  /*
   * We avoid multiple worker processes conflicting via the balloon mutex.
   * We may of course race updates of the target counts (which are protected
   * by the balloon lock), or with changes to the Xen hard limit, but we will
   * recover from these in time.
   */
  static void balloon_process(struct work_struct *work)
  {

  	enum bp_state state = BP_DONE;

  	long credit;
  
  	mutex_lock(&balloon_mutex);
  
  	do {

  		credit = current_credit();

  		if (credit > 0)

  			state = increase_reservation(credit);

  		if (credit < 0)

  			state = decrease_reservation(-credit, GFP_BALLOON);

  
  		state = update_schedule(state);

  
  #ifndef CONFIG_PREEMPT
  		if (need_resched())
  			schedule();
  #endif

  	} while (credit && state == BP_DONE);

  
  	/* Schedule more work if there is some still to be done. */

  	if (state == BP_EAGAIN)
  		schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);

  
  	mutex_unlock(&balloon_mutex);
  }
  
  /* Resets the Xen limit, sets new target, and kicks off processing. */

  void balloon_set_new_target(unsigned long target)

  {
  	/* No need for lock. Not read-modify-write updates. */

  	balloon_stats.target_pages = target;

  	schedule_delayed_work(&balloon_worker, 0);

  }

  EXPORT_SYMBOL_GPL(balloon_set_new_target);

  /**
   * alloc_xenballooned_pages - get pages that have been ballooned out
   * @nr_pages: Number of pages to get
   * @pages: pages returned
   * @return 0 on success, error otherwise
   */
  int alloc_xenballooned_pages(int nr_pages, struct page** pages)

  {

  	int pgno = 0;
  	struct page* page;
  	mutex_lock(&balloon_mutex);
  	while (pgno < nr_pages) {
  		page = balloon_retrieve(true);
  		if (page) {
  			pages[pgno++] = page;
  		} else {
  			enum bp_state st;
  			st = decrease_reservation(nr_pages - pgno, GFP_HIGHUSER);
  			if (st != BP_DONE)
  				goto out_undo;
  		}

  	}

  	mutex_unlock(&balloon_mutex);
  	return 0;
   out_undo:
  	while (pgno)
  		balloon_append(pages[--pgno]);
  	/* Free the memory back to the kernel soon */
  	schedule_delayed_work(&balloon_worker, 0);
  	mutex_unlock(&balloon_mutex);
  	return -ENOMEM;

  }

  EXPORT_SYMBOL(alloc_xenballooned_pages);

  /**
   * free_xenballooned_pages - return pages retrieved with get_ballooned_pages
   * @nr_pages: Number of pages
   * @pages: pages to return
   */
  void free_xenballooned_pages(int nr_pages, struct page** pages)

  {

  	int i;

  	mutex_lock(&balloon_mutex);

  	for (i = 0; i < nr_pages; i++) {
  		if (pages[i])
  			balloon_append(pages[i]);
  	}
  
  	/* The balloon may be too large now. Shrink it if needed. */

  	if (current_credit())

  		schedule_delayed_work(&balloon_worker, 0);

  	mutex_unlock(&balloon_mutex);
  }
  EXPORT_SYMBOL(free_xenballooned_pages);

  
  static int __init balloon_init(void)
  {

  	unsigned long pfn, extra_pfn_end;

  	struct page *page;

  	if (!xen_domain())

  		return -ENODEV;

  	pr_info("xen/balloon: Initialising balloon driver.
  ");

  	balloon_stats.current_pages = xen_pv_domain() ? min(xen_start_info->nr_pages, max_pfn) : max_pfn;

  	balloon_stats.target_pages  = balloon_stats.current_pages;
  	balloon_stats.balloon_low   = 0;
  	balloon_stats.balloon_high  = 0;

  	balloon_stats.schedule_delay = 1;
  	balloon_stats.max_schedule_delay = 32;
  	balloon_stats.retry_count = 1;

  	balloon_stats.max_retry_count = RETRY_UNLIMITED;

  	/*
  	 * Initialise the balloon with excess memory space.  We need
  	 * to make sure we don't add memory which doesn't exist or
  	 * logically exist.  The E820 map can be trimmed to be smaller
  	 * than the amount of physical memory due to the mem= command
  	 * line parameter.  And if this is a 32-bit non-HIGHMEM kernel
  	 * on a system with memory which requires highmem to access,
  	 * don't try to use it.
  	 */
  	extra_pfn_end = min(min(max_pfn, e820_end_of_ram_pfn()),

  			    (unsigned long)PFN_DOWN(xen_extra_mem_start + xen_extra_mem_size));

  	for (pfn = PFN_UP(xen_extra_mem_start);

  	     pfn < extra_pfn_end;

  	     pfn++) {

  		page = pfn_to_page(pfn);

  		/* totalram_pages and totalhigh_pages do not include the boot-time

  		   balloon extension, so don't subtract from it. */
  		__balloon_append(page);

  	}

  	return 0;
  }
  
  subsys_initcall(balloon_init);

  MODULE_LICENSE("GPL");