/*
   * Copyright (C) 2008, 2009 Intel Corporation
   * Authors: Andi Kleen, Fengguang Wu
   *
   * This software may be redistributed and/or modified under the terms of
   * the GNU General Public License ("GPL") version 2 only as published by the
   * Free Software Foundation.
   *
   * High level machine check handler. Handles pages reported by the

   * hardware as being corrupted usually due to a multi-bit ECC memory or cache

   * failure.

   * 
   * In addition there is a "soft offline" entry point that allows stop using
   * not-yet-corrupted-by-suspicious pages without killing anything.

   *
   * Handles page cache pages in various states.	The tricky part

   * here is that we can access any page asynchronously in respect to 
   * other VM users, because memory failures could happen anytime and 
   * anywhere. This could violate some of their assumptions. This is why 
   * this code has to be extremely careful. Generally it tries to use 
   * normal locking rules, as in get the standard locks, even if that means 
   * the error handling takes potentially a long time.
   * 
   * There are several operations here with exponential complexity because
   * of unsuitable VM data structures. For example the operation to map back 
   * from RMAP chains to processes has to walk the complete process list and 
   * has non linear complexity with the number. But since memory corruptions
   * are rare we hope to get away with this. This avoids impacting the core 
   * VM.

   */
  
  /*
   * Notebook:
   * - hugetlb needs more code
   * - kcore/oldmem/vmcore/mem/kmem check for hwpoison pages
   * - pass bad pages to kdump next kernel
   */

  #include <linux/kernel.h>
  #include <linux/mm.h>
  #include <linux/page-flags.h>

  #include <linux/kernel-page-flags.h>

  #include <linux/sched.h>

  #include <linux/ksm.h>

  #include <linux/rmap.h>
  #include <linux/pagemap.h>
  #include <linux/swap.h>
  #include <linux/backing-dev.h>

  #include <linux/migrate.h>
  #include <linux/page-isolation.h>
  #include <linux/suspend.h>

  #include <linux/slab.h>

  #include <linux/swapops.h>

  #include <linux/hugetlb.h>

  #include <linux/memory_hotplug.h>

  #include "internal.h"
  
  int sysctl_memory_failure_early_kill __read_mostly = 0;
  
  int sysctl_memory_failure_recovery __read_mostly = 1;
  
  atomic_long_t mce_bad_pages __read_mostly = ATOMIC_LONG_INIT(0);

  #if defined(CONFIG_HWPOISON_INJECT) || defined(CONFIG_HWPOISON_INJECT_MODULE)

  u32 hwpoison_filter_enable = 0;

  u32 hwpoison_filter_dev_major = ~0U;
  u32 hwpoison_filter_dev_minor = ~0U;

  u64 hwpoison_filter_flags_mask;
  u64 hwpoison_filter_flags_value;

  EXPORT_SYMBOL_GPL(hwpoison_filter_enable);

  EXPORT_SYMBOL_GPL(hwpoison_filter_dev_major);
  EXPORT_SYMBOL_GPL(hwpoison_filter_dev_minor);

  EXPORT_SYMBOL_GPL(hwpoison_filter_flags_mask);
  EXPORT_SYMBOL_GPL(hwpoison_filter_flags_value);

  
  static int hwpoison_filter_dev(struct page *p)
  {
  	struct address_space *mapping;
  	dev_t dev;
  
  	if (hwpoison_filter_dev_major == ~0U &&
  	    hwpoison_filter_dev_minor == ~0U)
  		return 0;
  
  	/*

  	 * page_mapping() does not accept slab pages.

  	 */
  	if (PageSlab(p))
  		return -EINVAL;
  
  	mapping = page_mapping(p);
  	if (mapping == NULL || mapping->host == NULL)
  		return -EINVAL;
  
  	dev = mapping->host->i_sb->s_dev;
  	if (hwpoison_filter_dev_major != ~0U &&
  	    hwpoison_filter_dev_major != MAJOR(dev))
  		return -EINVAL;
  	if (hwpoison_filter_dev_minor != ~0U &&
  	    hwpoison_filter_dev_minor != MINOR(dev))
  		return -EINVAL;
  
  	return 0;
  }

  static int hwpoison_filter_flags(struct page *p)
  {
  	if (!hwpoison_filter_flags_mask)
  		return 0;
  
  	if ((stable_page_flags(p) & hwpoison_filter_flags_mask) ==
  				    hwpoison_filter_flags_value)
  		return 0;
  	else
  		return -EINVAL;
  }

  /*
   * This allows stress tests to limit test scope to a collection of tasks
   * by putting them under some memcg. This prevents killing unrelated/important
   * processes such as /sbin/init. Note that the target task may share clean
   * pages with init (eg. libc text), which is harmless. If the target task
   * share _dirty_ pages with another task B, the test scheme must make sure B
   * is also included in the memcg. At last, due to race conditions this filter
   * can only guarantee that the page either belongs to the memcg tasks, or is
   * a freed page.
   */
  #ifdef	CONFIG_CGROUP_MEM_RES_CTLR_SWAP
  u64 hwpoison_filter_memcg;
  EXPORT_SYMBOL_GPL(hwpoison_filter_memcg);
  static int hwpoison_filter_task(struct page *p)
  {
  	struct mem_cgroup *mem;
  	struct cgroup_subsys_state *css;
  	unsigned long ino;
  
  	if (!hwpoison_filter_memcg)
  		return 0;
  
  	mem = try_get_mem_cgroup_from_page(p);
  	if (!mem)
  		return -EINVAL;
  
  	css = mem_cgroup_css(mem);
  	/* root_mem_cgroup has NULL dentries */
  	if (!css->cgroup->dentry)
  		return -EINVAL;
  
  	ino = css->cgroup->dentry->d_inode->i_ino;
  	css_put(css);
  
  	if (ino != hwpoison_filter_memcg)
  		return -EINVAL;
  
  	return 0;
  }
  #else
  static int hwpoison_filter_task(struct page *p) { return 0; }
  #endif

  int hwpoison_filter(struct page *p)
  {

  	if (!hwpoison_filter_enable)
  		return 0;

  	if (hwpoison_filter_dev(p))
  		return -EINVAL;

  	if (hwpoison_filter_flags(p))
  		return -EINVAL;

  	if (hwpoison_filter_task(p))
  		return -EINVAL;

  	return 0;
  }

  #else
  int hwpoison_filter(struct page *p)
  {
  	return 0;
  }
  #endif

  EXPORT_SYMBOL_GPL(hwpoison_filter);

  /*
   * Send all the processes who have the page mapped an ``action optional''
   * signal.
   */
  static int kill_proc_ao(struct task_struct *t, unsigned long addr, int trapno,

  			unsigned long pfn, struct page *page)

  {
  	struct siginfo si;
  	int ret;
  
  	printk(KERN_ERR
  		"MCE %#lx: Killing %s:%d early due to hardware memory corruption
  ",
  		pfn, t->comm, t->pid);
  	si.si_signo = SIGBUS;
  	si.si_errno = 0;
  	si.si_code = BUS_MCEERR_AO;
  	si.si_addr = (void *)addr;
  #ifdef __ARCH_SI_TRAPNO
  	si.si_trapno = trapno;
  #endif

  	si.si_addr_lsb = compound_order(compound_head(page)) + PAGE_SHIFT;

  	/*
  	 * Don't use force here, it's convenient if the signal
  	 * can be temporarily blocked.
  	 * This could cause a loop when the user sets SIGBUS
  	 * to SIG_IGN, but hopefully noone will do that?
  	 */
  	ret = send_sig_info(SIGBUS, &si, t);  /* synchronous? */
  	if (ret < 0)
  		printk(KERN_INFO "MCE: Error sending signal to %s:%d: %d
  ",
  		       t->comm, t->pid, ret);
  	return ret;
  }
  
  /*

   * When a unknown page type is encountered drain as many buffers as possible
   * in the hope to turn the page into a LRU or free page, which we can handle.
   */

  void shake_page(struct page *p, int access)

  {
  	if (!PageSlab(p)) {
  		lru_add_drain_all();
  		if (PageLRU(p))
  			return;
  		drain_all_pages();
  		if (PageLRU(p) || is_free_buddy_page(p))
  			return;
  	}

  	/*

  	 * Only all shrink_slab here (which would also
  	 * shrink other caches) if access is not potentially fatal.

  	 */

  	if (access) {
  		int nr;
  		do {
  			nr = shrink_slab(1000, GFP_KERNEL, 1000);

  			if (page_count(p) == 1)

  				break;
  		} while (nr > 10);
  	}

  }
  EXPORT_SYMBOL_GPL(shake_page);
  
  /*

   * Kill all processes that have a poisoned page mapped and then isolate
   * the page.
   *
   * General strategy:
   * Find all processes having the page mapped and kill them.
   * But we keep a page reference around so that the page is not
   * actually freed yet.
   * Then stash the page away
   *
   * There's no convenient way to get back to mapped processes
   * from the VMAs. So do a brute-force search over all
   * running processes.
   *
   * Remember that machine checks are not common (or rather
   * if they are common you have other problems), so this shouldn't
   * be a performance issue.
   *
   * Also there are some races possible while we get from the
   * error detection to actually handle it.
   */
  
  struct to_kill {
  	struct list_head nd;
  	struct task_struct *tsk;
  	unsigned long addr;

  	char addr_valid;

  };
  
  /*
   * Failure handling: if we can't find or can't kill a process there's
   * not much we can do.	We just print a message and ignore otherwise.
   */
  
  /*
   * Schedule a process for later kill.
   * Uses GFP_ATOMIC allocations to avoid potential recursions in the VM.
   * TBD would GFP_NOIO be enough?
   */
  static void add_to_kill(struct task_struct *tsk, struct page *p,
  		       struct vm_area_struct *vma,
  		       struct list_head *to_kill,
  		       struct to_kill **tkc)
  {
  	struct to_kill *tk;
  
  	if (*tkc) {
  		tk = *tkc;
  		*tkc = NULL;
  	} else {
  		tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC);
  		if (!tk) {
  			printk(KERN_ERR
  		"MCE: Out of memory while machine check handling
  ");
  			return;
  		}
  	}
  	tk->addr = page_address_in_vma(p, vma);
  	tk->addr_valid = 1;
  
  	/*
  	 * In theory we don't have to kill when the page was
  	 * munmaped. But it could be also a mremap. Since that's
  	 * likely very rare kill anyways just out of paranoia, but use
  	 * a SIGKILL because the error is not contained anymore.
  	 */
  	if (tk->addr == -EFAULT) {

  		pr_info("MCE: Unable to find user space address %lx in %s
  ",

  			page_to_pfn(p), tsk->comm);
  		tk->addr_valid = 0;
  	}
  	get_task_struct(tsk);
  	tk->tsk = tsk;
  	list_add_tail(&tk->nd, to_kill);
  }
  
  /*
   * Kill the processes that have been collected earlier.
   *
   * Only do anything when DOIT is set, otherwise just free the list
   * (this is used for clean pages which do not need killing)
   * Also when FAIL is set do a force kill because something went
   * wrong earlier.
   */
  static void kill_procs_ao(struct list_head *to_kill, int doit, int trapno,

  			  int fail, struct page *page, unsigned long pfn)

  {
  	struct to_kill *tk, *next;
  
  	list_for_each_entry_safe (tk, next, to_kill, nd) {
  		if (doit) {
  			/*

  			 * In case something went wrong with munmapping

  			 * make sure the process doesn't catch the
  			 * signal and then access the memory. Just kill it.

  			 */
  			if (fail || tk->addr_valid == 0) {
  				printk(KERN_ERR
  		"MCE %#lx: forcibly killing %s:%d because of failure to unmap corrupted page
  ",
  					pfn, tk->tsk->comm, tk->tsk->pid);
  				force_sig(SIGKILL, tk->tsk);
  			}
  
  			/*
  			 * In theory the process could have mapped
  			 * something else on the address in-between. We could
  			 * check for that, but we need to tell the
  			 * process anyways.
  			 */
  			else if (kill_proc_ao(tk->tsk, tk->addr, trapno,

  					      pfn, page) < 0)

  				printk(KERN_ERR
  		"MCE %#lx: Cannot send advisory machine check signal to %s:%d
  ",
  					pfn, tk->tsk->comm, tk->tsk->pid);
  		}
  		put_task_struct(tk->tsk);
  		kfree(tk);
  	}
  }
  
  static int task_early_kill(struct task_struct *tsk)
  {
  	if (!tsk->mm)
  		return 0;
  	if (tsk->flags & PF_MCE_PROCESS)
  		return !!(tsk->flags & PF_MCE_EARLY);
  	return sysctl_memory_failure_early_kill;
  }
  
  /*
   * Collect processes when the error hit an anonymous page.
   */
  static void collect_procs_anon(struct page *page, struct list_head *to_kill,
  			      struct to_kill **tkc)
  {
  	struct vm_area_struct *vma;
  	struct task_struct *tsk;
  	struct anon_vma *av;
  
  	read_lock(&tasklist_lock);
  	av = page_lock_anon_vma(page);
  	if (av == NULL)	/* Not actually mapped anymore */
  		goto out;
  	for_each_process (tsk) {

  		struct anon_vma_chain *vmac;

  		if (!task_early_kill(tsk))
  			continue;

  		list_for_each_entry(vmac, &av->head, same_anon_vma) {
  			vma = vmac->vma;

  			if (!page_mapped_in_vma(page, vma))
  				continue;
  			if (vma->vm_mm == tsk->mm)
  				add_to_kill(tsk, page, vma, to_kill, tkc);
  		}
  	}
  	page_unlock_anon_vma(av);
  out:
  	read_unlock(&tasklist_lock);
  }
  
  /*
   * Collect processes when the error hit a file mapped page.
   */
  static void collect_procs_file(struct page *page, struct list_head *to_kill,
  			      struct to_kill **tkc)
  {
  	struct vm_area_struct *vma;
  	struct task_struct *tsk;
  	struct prio_tree_iter iter;
  	struct address_space *mapping = page->mapping;
  
  	/*
  	 * A note on the locking order between the two locks.
  	 * We don't rely on this particular order.
  	 * If you have some other code that needs a different order
  	 * feel free to switch them around. Or add a reverse link
  	 * from mm_struct to task_struct, then this could be all
  	 * done without taking tasklist_lock and looping over all tasks.
  	 */
  
  	read_lock(&tasklist_lock);
  	spin_lock(&mapping->i_mmap_lock);
  	for_each_process(tsk) {
  		pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
  
  		if (!task_early_kill(tsk))
  			continue;
  
  		vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff,
  				      pgoff) {
  			/*
  			 * Send early kill signal to tasks where a vma covers
  			 * the page but the corrupted page is not necessarily
  			 * mapped it in its pte.
  			 * Assume applications who requested early kill want
  			 * to be informed of all such data corruptions.
  			 */
  			if (vma->vm_mm == tsk->mm)
  				add_to_kill(tsk, page, vma, to_kill, tkc);
  		}
  	}
  	spin_unlock(&mapping->i_mmap_lock);
  	read_unlock(&tasklist_lock);
  }
  
  /*
   * Collect the processes who have the corrupted page mapped to kill.
   * This is done in two steps for locking reasons.
   * First preallocate one tokill structure outside the spin locks,
   * so that we can kill at least one process reasonably reliable.
   */
  static void collect_procs(struct page *page, struct list_head *tokill)
  {
  	struct to_kill *tk;
  
  	if (!page->mapping)
  		return;
  
  	tk = kmalloc(sizeof(struct to_kill), GFP_NOIO);
  	if (!tk)
  		return;
  	if (PageAnon(page))
  		collect_procs_anon(page, tokill, &tk);
  	else
  		collect_procs_file(page, tokill, &tk);
  	kfree(tk);
  }
  
  /*
   * Error handlers for various types of pages.
   */
  
  enum outcome {

  	IGNORED,	/* Error: cannot be handled */
  	FAILED,		/* Error: handling failed */

  	DELAYED,	/* Will be handled later */

  	RECOVERED,	/* Successfully recovered */
  };
  
  static const char *action_name[] = {

  	[IGNORED] = "Ignored",

  	[FAILED] = "Failed",
  	[DELAYED] = "Delayed",

  	[RECOVERED] = "Recovered",
  };
  
  /*

   * XXX: It is possible that a page is isolated from LRU cache,
   * and then kept in swap cache or failed to remove from page cache.
   * The page count will stop it from being freed by unpoison.
   * Stress tests should be aware of this memory leak problem.
   */
  static int delete_from_lru_cache(struct page *p)
  {
  	if (!isolate_lru_page(p)) {
  		/*
  		 * Clear sensible page flags, so that the buddy system won't
  		 * complain when the page is unpoison-and-freed.
  		 */
  		ClearPageActive(p);
  		ClearPageUnevictable(p);
  		/*
  		 * drop the page count elevated by isolate_lru_page()
  		 */
  		page_cache_release(p);
  		return 0;
  	}
  	return -EIO;
  }
  
  /*

   * Error hit kernel page.
   * Do nothing, try to be lucky and not touch this instead. For a few cases we
   * could be more sophisticated.
   */
  static int me_kernel(struct page *p, unsigned long pfn)
  {

  	return IGNORED;
  }
  
  /*
   * Page in unknown state. Do nothing.
   */
  static int me_unknown(struct page *p, unsigned long pfn)
  {
  	printk(KERN_ERR "MCE %#lx: Unknown page state
  ", pfn);
  	return FAILED;
  }
  
  /*

   * Clean (or cleaned) page cache page.
   */
  static int me_pagecache_clean(struct page *p, unsigned long pfn)
  {
  	int err;
  	int ret = FAILED;
  	struct address_space *mapping;

  	delete_from_lru_cache(p);

  	/*
  	 * For anonymous pages we're done the only reference left
  	 * should be the one m_f() holds.
  	 */
  	if (PageAnon(p))
  		return RECOVERED;
  
  	/*
  	 * Now truncate the page in the page cache. This is really
  	 * more like a "temporary hole punch"
  	 * Don't do this for block devices when someone else
  	 * has a reference, because it could be file system metadata
  	 * and that's not safe to truncate.
  	 */
  	mapping = page_mapping(p);
  	if (!mapping) {
  		/*
  		 * Page has been teared down in the meanwhile
  		 */
  		return FAILED;
  	}
  
  	/*
  	 * Truncation is a bit tricky. Enable it per file system for now.
  	 *
  	 * Open: to take i_mutex or not for this? Right now we don't.
  	 */
  	if (mapping->a_ops->error_remove_page) {
  		err = mapping->a_ops->error_remove_page(mapping, p);
  		if (err != 0) {
  			printk(KERN_INFO "MCE %#lx: Failed to punch page: %d
  ",
  					pfn, err);
  		} else if (page_has_private(p) &&
  				!try_to_release_page(p, GFP_NOIO)) {

  			pr_info("MCE %#lx: failed to release buffers
  ", pfn);

  		} else {
  			ret = RECOVERED;
  		}
  	} else {
  		/*
  		 * If the file system doesn't support it just invalidate
  		 * This fails on dirty or anything with private pages
  		 */
  		if (invalidate_inode_page(p))
  			ret = RECOVERED;
  		else
  			printk(KERN_INFO "MCE %#lx: Failed to invalidate
  ",
  				pfn);
  	}
  	return ret;
  }
  
  /*
   * Dirty cache page page
   * Issues: when the error hit a hole page the error is not properly
   * propagated.
   */
  static int me_pagecache_dirty(struct page *p, unsigned long pfn)
  {
  	struct address_space *mapping = page_mapping(p);
  
  	SetPageError(p);
  	/* TBD: print more information about the file. */
  	if (mapping) {
  		/*
  		 * IO error will be reported by write(), fsync(), etc.
  		 * who check the mapping.
  		 * This way the application knows that something went
  		 * wrong with its dirty file data.
  		 *
  		 * There's one open issue:
  		 *
  		 * The EIO will be only reported on the next IO
  		 * operation and then cleared through the IO map.
  		 * Normally Linux has two mechanisms to pass IO error
  		 * first through the AS_EIO flag in the address space
  		 * and then through the PageError flag in the page.
  		 * Since we drop pages on memory failure handling the
  		 * only mechanism open to use is through AS_AIO.
  		 *
  		 * This has the disadvantage that it gets cleared on
  		 * the first operation that returns an error, while
  		 * the PageError bit is more sticky and only cleared
  		 * when the page is reread or dropped.  If an
  		 * application assumes it will always get error on
  		 * fsync, but does other operations on the fd before
  		 * and the page is dropped inbetween then the error
  		 * will not be properly reported.
  		 *
  		 * This can already happen even without hwpoisoned
  		 * pages: first on metadata IO errors (which only
  		 * report through AS_EIO) or when the page is dropped
  		 * at the wrong time.
  		 *
  		 * So right now we assume that the application DTRT on
  		 * the first EIO, but we're not worse than other parts
  		 * of the kernel.
  		 */
  		mapping_set_error(mapping, EIO);
  	}
  
  	return me_pagecache_clean(p, pfn);
  }
  
  /*
   * Clean and dirty swap cache.
   *
   * Dirty swap cache page is tricky to handle. The page could live both in page
   * cache and swap cache(ie. page is freshly swapped in). So it could be
   * referenced concurrently by 2 types of PTEs:
   * normal PTEs and swap PTEs. We try to handle them consistently by calling
   * try_to_unmap(TTU_IGNORE_HWPOISON) to convert the normal PTEs to swap PTEs,
   * and then
   *      - clear dirty bit to prevent IO
   *      - remove from LRU
   *      - but keep in the swap cache, so that when we return to it on
   *        a later page fault, we know the application is accessing
   *        corrupted data and shall be killed (we installed simple
   *        interception code in do_swap_page to catch it).
   *
   * Clean swap cache pages can be directly isolated. A later page fault will
   * bring in the known good data from disk.
   */
  static int me_swapcache_dirty(struct page *p, unsigned long pfn)
  {

  	ClearPageDirty(p);
  	/* Trigger EIO in shmem: */
  	ClearPageUptodate(p);

  	if (!delete_from_lru_cache(p))
  		return DELAYED;
  	else
  		return FAILED;

  }
  
  static int me_swapcache_clean(struct page *p, unsigned long pfn)
  {

  	delete_from_swap_cache(p);

  	if (!delete_from_lru_cache(p))
  		return RECOVERED;
  	else
  		return FAILED;

  }
  
  /*
   * Huge pages. Needs work.
   * Issues:

   * - Error on hugepage is contained in hugepage unit (not in raw page unit.)
   *   To narrow down kill region to one page, we need to break up pmd.

   */
  static int me_huge_page(struct page *p, unsigned long pfn)
  {

  	int res = 0;

  	struct page *hpage = compound_head(p);
  	/*
  	 * We can safely recover from error on free or reserved (i.e.
  	 * not in-use) hugepage by dequeuing it from freelist.
  	 * To check whether a hugepage is in-use or not, we can't use
  	 * page->lru because it can be used in other hugepage operations,
  	 * such as __unmap_hugepage_range() and gather_surplus_pages().
  	 * So instead we use page_mapping() and PageAnon().
  	 * We assume that this function is called with page lock held,
  	 * so there is no race between isolation and mapping/unmapping.
  	 */
  	if (!(page_mapping(hpage) || PageAnon(hpage))) {

  		res = dequeue_hwpoisoned_huge_page(hpage);
  		if (!res)
  			return RECOVERED;

  	}
  	return DELAYED;

  }
  
  /*
   * Various page states we can handle.
   *
   * A page state is defined by its current page->flags bits.
   * The table matches them in order and calls the right handler.
   *
   * This is quite tricky because we can access page at any time
   * in its live cycle, so all accesses have to be extremly careful.
   *
   * This is not complete. More states could be added.
   * For any missing state don't attempt recovery.
   */
  
  #define dirty		(1UL << PG_dirty)
  #define sc		(1UL << PG_swapcache)
  #define unevict		(1UL << PG_unevictable)
  #define mlock		(1UL << PG_mlocked)
  #define writeback	(1UL << PG_writeback)
  #define lru		(1UL << PG_lru)
  #define swapbacked	(1UL << PG_swapbacked)
  #define head		(1UL << PG_head)
  #define tail		(1UL << PG_tail)
  #define compound	(1UL << PG_compound)
  #define slab		(1UL << PG_slab)

  #define reserved	(1UL << PG_reserved)
  
  static struct page_state {
  	unsigned long mask;
  	unsigned long res;
  	char *msg;
  	int (*action)(struct page *p, unsigned long pfn);
  } error_states[] = {

  	{ reserved,	reserved,	"reserved kernel",	me_kernel },

  	/*
  	 * free pages are specially detected outside this table:
  	 * PG_buddy pages only make a small fraction of all free pages.
  	 */

  
  	/*
  	 * Could in theory check if slab page is free or if we can drop
  	 * currently unused objects without touching them. But just
  	 * treat it as standard kernel for now.
  	 */
  	{ slab,		slab,		"kernel slab",	me_kernel },
  
  #ifdef CONFIG_PAGEFLAGS_EXTENDED
  	{ head,		head,		"huge",		me_huge_page },
  	{ tail,		tail,		"huge",		me_huge_page },
  #else
  	{ compound,	compound,	"huge",		me_huge_page },
  #endif
  
  	{ sc|dirty,	sc|dirty,	"swapcache",	me_swapcache_dirty },
  	{ sc|dirty,	sc,		"swapcache",	me_swapcache_clean },
  
  	{ unevict|dirty, unevict|dirty,	"unevictable LRU", me_pagecache_dirty},
  	{ unevict,	unevict,	"unevictable LRU", me_pagecache_clean},

  	{ mlock|dirty,	mlock|dirty,	"mlocked LRU",	me_pagecache_dirty },
  	{ mlock,	mlock,		"mlocked LRU",	me_pagecache_clean },

  
  	{ lru|dirty,	lru|dirty,	"LRU",		me_pagecache_dirty },
  	{ lru|dirty,	lru,		"clean LRU",	me_pagecache_clean },

  
  	/*
  	 * Catchall entry: must be at end.
  	 */
  	{ 0,		0,		"unknown page state",	me_unknown },
  };

  #undef dirty
  #undef sc
  #undef unevict
  #undef mlock
  #undef writeback
  #undef lru
  #undef swapbacked
  #undef head
  #undef tail
  #undef compound
  #undef slab
  #undef reserved

  static void action_result(unsigned long pfn, char *msg, int result)
  {

  	struct page *page = pfn_to_page(pfn);

  
  	printk(KERN_ERR "MCE %#lx: %s%s page recovery: %s
  ",
  		pfn,

  		PageDirty(page) ? "dirty " : "",

  		msg, action_name[result]);
  }
  
  static int page_action(struct page_state *ps, struct page *p,

  			unsigned long pfn)

  {
  	int result;

  	int count;

  
  	result = ps->action(p, pfn);
  	action_result(pfn, ps->msg, result);

  	count = page_count(p) - 1;

  	if (ps->action == me_swapcache_dirty && result == DELAYED)
  		count--;
  	if (count != 0) {

  		printk(KERN_ERR
  		       "MCE %#lx: %s page still referenced by %d users
  ",

  		       pfn, ps->msg, count);

  		result = FAILED;
  	}

  
  	/* Could do more checks here if page looks ok */
  	/*
  	 * Could adjust zone counters here to correct for the missing page.
  	 */

  	return (result == RECOVERED || result == DELAYED) ? 0 : -EBUSY;

  }

  /*
   * Do all that is necessary to remove user space mappings. Unmap
   * the pages and send SIGBUS to the processes if the data was dirty.
   */

  static int hwpoison_user_mappings(struct page *p, unsigned long pfn,

  				  int trapno)
  {
  	enum ttu_flags ttu = TTU_UNMAP | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
  	struct address_space *mapping;
  	LIST_HEAD(tokill);
  	int ret;

  	int kill = 1;

  	struct page *hpage = compound_head(p);

  	if (PageReserved(p) || PageSlab(p))
  		return SWAP_SUCCESS;

  	/*
  	 * This check implies we don't kill processes if their pages
  	 * are in the swap cache early. Those are always late kills.
  	 */

  	if (!page_mapped(hpage))

  		return SWAP_SUCCESS;

  	if (PageKsm(p))

  		return SWAP_FAIL;

  
  	if (PageSwapCache(p)) {
  		printk(KERN_ERR
  		       "MCE %#lx: keeping poisoned page in swap cache
  ", pfn);
  		ttu |= TTU_IGNORE_HWPOISON;
  	}
  
  	/*
  	 * Propagate the dirty bit from PTEs to struct page first, because we
  	 * need this to decide if we should kill or just drop the page.

  	 * XXX: the dirty test could be racy: set_page_dirty() may not always
  	 * be called inside page lock (it's recommended but not enforced).

  	 */

  	mapping = page_mapping(hpage);
  	if (!PageDirty(hpage) && mapping &&
  	    mapping_cap_writeback_dirty(mapping)) {
  		if (page_mkclean(hpage)) {
  			SetPageDirty(hpage);

  		} else {
  			kill = 0;
  			ttu |= TTU_IGNORE_HWPOISON;
  			printk(KERN_INFO
  	"MCE %#lx: corrupted page was clean: dropped without side effects
  ",
  				pfn);
  		}
  	}
  
  	/*
  	 * First collect all the processes that have the page
  	 * mapped in dirty form.  This has to be done before try_to_unmap,
  	 * because ttu takes the rmap data structures down.
  	 *
  	 * Error handling: We ignore errors here because
  	 * there's nothing that can be done.
  	 */
  	if (kill)

  		collect_procs(hpage, &tokill);

  	ret = try_to_unmap(hpage, ttu);

  	if (ret != SWAP_SUCCESS)
  		printk(KERN_ERR "MCE %#lx: failed to unmap page (mapcount=%d)
  ",

  				pfn, page_mapcount(hpage));

  
  	/*
  	 * Now that the dirty bit has been propagated to the
  	 * struct page and all unmaps done we can decide if
  	 * killing is needed or not.  Only kill when the page
  	 * was dirty, otherwise the tokill list is merely
  	 * freed.  When there was a problem unmapping earlier
  	 * use a more force-full uncatchable kill to prevent
  	 * any accesses to the poisoned memory.
  	 */

  	kill_procs_ao(&tokill, !!PageDirty(hpage), trapno,

  		      ret != SWAP_SUCCESS, p, pfn);

  
  	return ret;

  }

  static void set_page_hwpoison_huge_page(struct page *hpage)
  {
  	int i;
  	int nr_pages = 1 << compound_order(hpage);
  	for (i = 0; i < nr_pages; i++)
  		SetPageHWPoison(hpage + i);
  }
  
  static void clear_page_hwpoison_huge_page(struct page *hpage)
  {
  	int i;
  	int nr_pages = 1 << compound_order(hpage);
  	for (i = 0; i < nr_pages; i++)
  		ClearPageHWPoison(hpage + i);
  }

  int __memory_failure(unsigned long pfn, int trapno, int flags)

  {
  	struct page_state *ps;
  	struct page *p;

  	struct page *hpage;

  	int res;

  	unsigned int nr_pages;

  
  	if (!sysctl_memory_failure_recovery)
  		panic("Memory failure from trap %d on page %lx", trapno, pfn);
  
  	if (!pfn_valid(pfn)) {

  		printk(KERN_ERR
  		       "MCE %#lx: memory outside kernel control
  ",
  		       pfn);
  		return -ENXIO;

  	}
  
  	p = pfn_to_page(pfn);

  	hpage = compound_head(p);

  	if (TestSetPageHWPoison(p)) {

  		printk(KERN_ERR "MCE %#lx: already hardware poisoned
  ", pfn);

  		return 0;
  	}

  	nr_pages = 1 << compound_order(hpage);
  	atomic_long_add(nr_pages, &mce_bad_pages);

  
  	/*
  	 * We need/can do nothing about count=0 pages.
  	 * 1) it's a free page, and therefore in safe hand:
  	 *    prep_new_page() will be the gate keeper.

  	 * 2) it's a free hugepage, which is also safe:
  	 *    an affected hugepage will be dequeued from hugepage freelist,
  	 *    so there's no concern about reusing it ever after.
  	 * 3) it's part of a non-compound high order page.

  	 *    Implies some kernel user: cannot stop them from
  	 *    R/W the page; let's pray that the page has been
  	 *    used and will be freed some time later.
  	 * In fact it's dangerous to directly bump up page count from 0,
  	 * that may make page_freeze_refs()/page_unfreeze_refs() mismatch.
  	 */

  	if (!(flags & MF_COUNT_INCREASED) &&

  		!get_page_unless_zero(hpage)) {

  		if (is_free_buddy_page(p)) {
  			action_result(pfn, "free buddy", DELAYED);
  			return 0;

  		} else if (PageHuge(hpage)) {
  			/*
  			 * Check "just unpoisoned", "filter hit", and
  			 * "race with other subpage."
  			 */
  			lock_page_nosync(hpage);
  			if (!PageHWPoison(hpage)
  			    || (hwpoison_filter(p) && TestClearPageHWPoison(p))
  			    || (p != hpage && TestSetPageHWPoison(hpage))) {
  				atomic_long_sub(nr_pages, &mce_bad_pages);
  				return 0;
  			}
  			set_page_hwpoison_huge_page(hpage);
  			res = dequeue_hwpoisoned_huge_page(hpage);
  			action_result(pfn, "free huge",
  				      res ? IGNORED : DELAYED);
  			unlock_page(hpage);
  			return res;

  		} else {
  			action_result(pfn, "high order kernel", IGNORED);
  			return -EBUSY;
  		}

  	}
  
  	/*

  	 * We ignore non-LRU pages for good reasons.
  	 * - PG_locked is only well defined for LRU pages and a few others
  	 * - to avoid races with __set_page_locked()
  	 * - to avoid races with __SetPageSlab*() (and more non-atomic ops)
  	 * The check (unnecessarily) ignores LRU pages being isolated and
  	 * walked by the page reclaim code, however that's not a big loss.
  	 */

  	if (!PageLRU(p) && !PageHuge(p))

  		shake_page(p, 0);

  	if (!PageLRU(p) && !PageHuge(p)) {

  		/*
  		 * shake_page could have turned it free.
  		 */
  		if (is_free_buddy_page(p)) {
  			action_result(pfn, "free buddy, 2nd try", DELAYED);
  			return 0;
  		}

  		action_result(pfn, "non LRU", IGNORED);
  		put_page(p);
  		return -EBUSY;
  	}

  
  	/*

  	 * Lock the page and wait for writeback to finish.
  	 * It's very difficult to mess with pages currently under IO
  	 * and in many cases impossible, so we just avoid it here.
  	 */

  	lock_page_nosync(hpage);

  
  	/*
  	 * unpoison always clear PG_hwpoison inside page lock
  	 */
  	if (!PageHWPoison(p)) {

  		printk(KERN_ERR "MCE %#lx: just unpoisoned
  ", pfn);

  		res = 0;
  		goto out;
  	}

  	if (hwpoison_filter(p)) {
  		if (TestClearPageHWPoison(p))

  			atomic_long_sub(nr_pages, &mce_bad_pages);

  		unlock_page(hpage);
  		put_page(hpage);

  		return 0;
  	}

  	/*
  	 * For error on the tail page, we should set PG_hwpoison
  	 * on the head page to show that the hugepage is hwpoisoned
  	 */
  	if (PageTail(p) && TestSetPageHWPoison(hpage)) {
  		action_result(pfn, "hugepage already hardware poisoned",
  				IGNORED);
  		unlock_page(hpage);
  		put_page(hpage);
  		return 0;
  	}
  	/*
  	 * Set PG_hwpoison on all pages in an error hugepage,
  	 * because containment is done in hugepage unit for now.
  	 * Since we have done TestSetPageHWPoison() for the head page with
  	 * page lock held, we can safely set PG_hwpoison bits on tail pages.
  	 */
  	if (PageHuge(p))
  		set_page_hwpoison_huge_page(hpage);

  	wait_on_page_writeback(p);
  
  	/*
  	 * Now take care of user space mappings.

  	 * Abort on fail: __remove_from_page_cache() assumes unmapped page.

  	 */

  	if (hwpoison_user_mappings(p, pfn, trapno) != SWAP_SUCCESS) {
  		printk(KERN_ERR "MCE %#lx: cannot unmap page, give up
  ", pfn);
  		res = -EBUSY;
  		goto out;
  	}

  
  	/*
  	 * Torn down by someone else?
  	 */

  	if (PageLRU(p) && !PageSwapCache(p) && p->mapping == NULL) {

  		action_result(pfn, "already truncated LRU", IGNORED);

  		res = -EBUSY;

  		goto out;
  	}
  
  	res = -EBUSY;
  	for (ps = error_states;; ps++) {

  		if ((p->flags & ps->mask) == ps->res) {

  			res = page_action(ps, p, pfn);

  			break;
  		}
  	}
  out:

  	unlock_page(hpage);

  	return res;
  }
  EXPORT_SYMBOL_GPL(__memory_failure);
  
  /**
   * memory_failure - Handle memory failure of a page.
   * @pfn: Page Number of the corrupted page
   * @trapno: Trap number reported in the signal to user space.
   *
   * This function is called by the low level machine check code
   * of an architecture when it detects hardware memory corruption
   * of a page. It tries its best to recover, which includes
   * dropping pages, killing processes etc.
   *
   * The function is primarily of use for corruptions that
   * happen outside the current execution context (e.g. when
   * detected by a background scrubber)
   *
   * Must run in process context (e.g. a work queue) with interrupts
   * enabled and no spinlocks hold.
   */
  void memory_failure(unsigned long pfn, int trapno)
  {
  	__memory_failure(pfn, trapno, 0);
  }

  
  /**
   * unpoison_memory - Unpoison a previously poisoned page
   * @pfn: Page number of the to be unpoisoned page
   *
   * Software-unpoison a page that has been poisoned by
   * memory_failure() earlier.
   *
   * This is only done on the software-level, so it only works
   * for linux injected failures, not real hardware failures
   *
   * Returns 0 for success, otherwise -errno.
   */
  int unpoison_memory(unsigned long pfn)
  {
  	struct page *page;
  	struct page *p;
  	int freeit = 0;

  	unsigned int nr_pages;

  
  	if (!pfn_valid(pfn))
  		return -ENXIO;
  
  	p = pfn_to_page(pfn);
  	page = compound_head(p);
  
  	if (!PageHWPoison(p)) {

  		pr_info("MCE: Page was already unpoisoned %#lx
  ", pfn);

  		return 0;
  	}

  	nr_pages = 1 << compound_order(page);

  	if (!get_page_unless_zero(page)) {

  		/*
  		 * Since HWPoisoned hugepage should have non-zero refcount,
  		 * race between memory failure and unpoison seems to happen.
  		 * In such case unpoison fails and memory failure runs
  		 * to the end.
  		 */
  		if (PageHuge(page)) {
  			pr_debug("MCE: Memory failure is now running on free hugepage %#lx
  ", pfn);
  			return 0;
  		}

  		if (TestClearPageHWPoison(p))

  			atomic_long_sub(nr_pages, &mce_bad_pages);

  		pr_info("MCE: Software-unpoisoned free page %#lx
  ", pfn);

  		return 0;
  	}
  
  	lock_page_nosync(page);
  	/*
  	 * This test is racy because PG_hwpoison is set outside of page lock.
  	 * That's acceptable because that won't trigger kernel panic. Instead,
  	 * the PG_hwpoison page will be caught and isolated on the entrance to
  	 * the free buddy page pool.
  	 */

  	if (TestClearPageHWPoison(page)) {

  		pr_info("MCE: Software-unpoisoned page %#lx
  ", pfn);

  		atomic_long_sub(nr_pages, &mce_bad_pages);

  		freeit = 1;

  		if (PageHuge(page))
  			clear_page_hwpoison_huge_page(page);

  	}
  	unlock_page(page);
  
  	put_page(page);
  	if (freeit)
  		put_page(page);
  
  	return 0;
  }
  EXPORT_SYMBOL(unpoison_memory);

  
  static struct page *new_page(struct page *p, unsigned long private, int **x)
  {

  	int nid = page_to_nid(p);

  	if (PageHuge(p))
  		return alloc_huge_page_node(page_hstate(compound_head(p)),
  						   nid);
  	else
  		return alloc_pages_exact_node(nid, GFP_HIGHUSER_MOVABLE, 0);

  }
  
  /*
   * Safely get reference count of an arbitrary page.
   * Returns 0 for a free page, -EIO for a zero refcount page
   * that is not free, and 1 for any other page type.
   * For 1 the page is returned with increased page count, otherwise not.
   */
  static int get_any_page(struct page *p, unsigned long pfn, int flags)
  {
  	int ret;
  
  	if (flags & MF_COUNT_INCREASED)
  		return 1;
  
  	/*

  	 * The lock_memory_hotplug prevents a race with memory hotplug.

  	 * This is a big hammer, a better would be nicer.
  	 */

  	lock_memory_hotplug();

  
  	/*
  	 * Isolate the page, so that it doesn't get reallocated if it
  	 * was free.
  	 */
  	set_migratetype_isolate(p);

  	/*
  	 * When the target page is a free hugepage, just remove it
  	 * from free hugepage list.
  	 */

  	if (!get_page_unless_zero(compound_head(p))) {

  		if (PageHuge(p)) {

  			pr_info("get_any_page: %#lx free huge page
  ", pfn);

  			ret = dequeue_hwpoisoned_huge_page(compound_head(p));
  		} else if (is_free_buddy_page(p)) {

  			pr_info("get_any_page: %#lx free buddy page
  ", pfn);

  			/* Set hwpoison bit while page is still isolated */
  			SetPageHWPoison(p);
  			ret = 0;
  		} else {

  			pr_info("get_any_page: %#lx: unknown zero refcount page type %lx
  ",

  				pfn, p->flags);
  			ret = -EIO;
  		}
  	} else {
  		/* Not a free page */
  		ret = 1;
  	}
  	unset_migratetype_isolate(p);

  	unlock_memory_hotplug();

  	return ret;
  }

  static int soft_offline_huge_page(struct page *page, int flags)
  {
  	int ret;
  	unsigned long pfn = page_to_pfn(page);
  	struct page *hpage = compound_head(page);
  	LIST_HEAD(pagelist);
  
  	ret = get_any_page(page, pfn, flags);
  	if (ret < 0)
  		return ret;
  	if (ret == 0)
  		goto done;
  
  	if (PageHWPoison(hpage)) {
  		put_page(hpage);
  		pr_debug("soft offline: %#lx hugepage already poisoned
  ", pfn);
  		return -EBUSY;
  	}
  
  	/* Keep page count to indicate a given hugepage is isolated. */
  
  	list_add(&hpage->lru, &pagelist);
  	ret = migrate_huge_pages(&pagelist, new_page, MPOL_MF_MOVE_ALL, 0);
  	if (ret) {

  			putback_lru_pages(&pagelist);

  		pr_debug("soft offline: %#lx: migration failed %d, type %lx
  ",
  			 pfn, ret, page->flags);
  		if (ret > 0)
  			ret = -EIO;
  		return ret;
  	}
  done:
  	if (!PageHWPoison(hpage))
  		atomic_long_add(1 << compound_order(hpage), &mce_bad_pages);
  	set_page_hwpoison_huge_page(hpage);
  	dequeue_hwpoisoned_huge_page(hpage);
  	/* keep elevated page count for bad page */
  	return ret;
  }

  /**
   * soft_offline_page - Soft offline a page.
   * @page: page to offline
   * @flags: flags. Same as memory_failure().
   *
   * Returns 0 on success, otherwise negated errno.
   *
   * Soft offline a page, by migration or invalidation,
   * without killing anything. This is for the case when
   * a page is not corrupted yet (so it's still valid to access),
   * but has had a number of corrected errors and is better taken
   * out.
   *
   * The actual policy on when to do that is maintained by
   * user space.
   *
   * This should never impact any application or cause data loss,
   * however it might take some time.
   *
   * This is not a 100% solution for all memory, but tries to be
   * ``good enough'' for the majority of memory.
   */
  int soft_offline_page(struct page *page, int flags)
  {
  	int ret;
  	unsigned long pfn = page_to_pfn(page);

  	if (PageHuge(page))
  		return soft_offline_huge_page(page, flags);

  	ret = get_any_page(page, pfn, flags);
  	if (ret < 0)
  		return ret;
  	if (ret == 0)
  		goto done;
  
  	/*
  	 * Page cache page we can handle?
  	 */
  	if (!PageLRU(page)) {
  		/*
  		 * Try to free it.
  		 */
  		put_page(page);
  		shake_page(page, 1);
  
  		/*
  		 * Did it turn free?
  		 */
  		ret = get_any_page(page, pfn, 0);
  		if (ret < 0)
  			return ret;
  		if (ret == 0)
  			goto done;
  	}
  	if (!PageLRU(page)) {

  		pr_info("soft_offline: %#lx: unknown non LRU page type %lx
  ",

  				pfn, page->flags);
  		return -EIO;
  	}
  
  	lock_page(page);
  	wait_on_page_writeback(page);
  
  	/*
  	 * Synchronized using the page lock with memory_failure()
  	 */
  	if (PageHWPoison(page)) {
  		unlock_page(page);
  		put_page(page);

  		pr_info("soft offline: %#lx page already poisoned
  ", pfn);

  		return -EBUSY;
  	}
  
  	/*
  	 * Try to invalidate first. This should work for
  	 * non dirty unmapped page cache pages.
  	 */
  	ret = invalidate_inode_page(page);
  	unlock_page(page);
  
  	/*
  	 * Drop count because page migration doesn't like raised
  	 * counts. The page could get re-allocated, but if it becomes
  	 * LRU the isolation will just fail.
  	 * RED-PEN would be better to keep it isolated here, but we
  	 * would need to fix isolation locking first.
  	 */
  	put_page(page);
  	if (ret == 1) {
  		ret = 0;

  		pr_info("soft_offline: %#lx: invalidated
  ", pfn);

  		goto done;
  	}
  
  	/*
  	 * Simple invalidation didn't work.
  	 * Try to migrate to a new page instead. migrate.c
  	 * handles a large number of cases for us.
  	 */
  	ret = isolate_lru_page(page);
  	if (!ret) {
  		LIST_HEAD(pagelist);
  
  		list_add(&page->lru, &pagelist);
  		ret = migrate_pages(&pagelist, new_page, MPOL_MF_MOVE_ALL, 0);
  		if (ret) {

  			pr_info("soft offline: %#lx: migration failed %d, type %lx
  ",

  				pfn, ret, page->flags);
  			if (ret > 0)
  				ret = -EIO;
  		}
  	} else {

  		pr_info("soft offline: %#lx: isolation failed: %d, page count %d, type %lx
  ",

  				pfn, ret, page_count(page), page->flags);
  	}
  	if (ret)
  		return ret;
  
  done:
  	atomic_long_add(1, &mce_bad_pages);
  	SetPageHWPoison(page);
  	/* keep elevated page count for bad page */
  	return ret;
  }

  /*
   * The caller must hold current->mm->mmap_sem in read mode.
   */

  int is_hwpoison_address(unsigned long addr)
  {
  	pgd_t *pgdp;
  	pud_t pud, *pudp;
  	pmd_t pmd, *pmdp;
  	pte_t pte, *ptep;
  	swp_entry_t entry;
  
  	pgdp = pgd_offset(current->mm, addr);
  	if (!pgd_present(*pgdp))
  		return 0;
  	pudp = pud_offset(pgdp, addr);
  	pud = *pudp;
  	if (!pud_present(pud) || pud_large(pud))
  		return 0;
  	pmdp = pmd_offset(pudp, addr);
  	pmd = *pmdp;
  	if (!pmd_present(pmd) || pmd_large(pmd))
  		return 0;
  	ptep = pte_offset_map(pmdp, addr);
  	pte = *ptep;
  	pte_unmap(ptep);
  	if (!is_swap_pte(pte))
  		return 0;
  	entry = pte_to_swp_entry(pte);
  	return is_hwpoison_entry(entry);
  }
  EXPORT_SYMBOL_GPL(is_hwpoison_address);