// SPDX-License-Identifier: GPL-2.0-only

  /*
   * Copyright (C) 2008, 2009 Intel Corporation
   * Authors: Andi Kleen, Fengguang Wu
   *

   * 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.

   *
   * It can be very tempting to add handling for obscure cases here.
   * In general any code for handling new cases should only be added iff:
   * - You know how to test it.
   * - You have a test that can be added to mce-test
   *   https://git.kernel.org/cgit/utils/cpu/mce/mce-test.git/
   * - The case actually shows up as a frequent (top 10) page state in
   *   tools/vm/page-types when running a real workload.

   * 
   * 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.

   */

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

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

  #include <linux/sched/signal.h>

  #include <linux/sched/task.h>

  #include <linux/ksm.h>

  #include <linux/rmap.h>

  #include <linux/export.h>

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

  #include <linux/migrate.h>

  #include <linux/suspend.h>

  #include <linux/slab.h>

  #include <linux/swapops.h>

  #include <linux/hugetlb.h>

  #include <linux/memory_hotplug.h>

  #include <linux/mm_inline.h>

  #include <linux/memremap.h>

  #include <linux/kfifo.h>

  #include <linux/ratelimit.h>

  #include <linux/page-isolation.h>

  #include "internal.h"

  #include "ras/ras_event.h"

  
  int sysctl_memory_failure_early_kill __read_mostly = 0;
  
  int sysctl_memory_failure_recovery __read_mostly = 1;

  atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);

  static bool page_handle_poison(struct page *page, bool hugepage_or_freepage, bool release)

  {

  	if (hugepage_or_freepage) {
  		/*
  		 * Doing this check for free pages is also fine since dissolve_free_huge_page
  		 * returns 0 for non-hugetlb pages as well.
  		 */
  		if (dissolve_free_huge_page(page) || !take_page_off_buddy(page))
  			/*
  			 * We could fail to take off the target page from buddy
  			 * for example due to racy page allocaiton, but that's
  			 * acceptable because soft-offlined page is not broken
  			 * and if someone really want to use it, they should
  			 * take it.
  			 */
  			return false;
  	}

  	SetPageHWPoison(page);

  	if (release)
  		put_page(page);

  	page_ref_inc(page);
  	num_poisoned_pages_inc();

  
  	return true;

  }

  #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_MEMCG

  u64 hwpoison_filter_memcg;
  EXPORT_SYMBOL_GPL(hwpoison_filter_memcg);
  static int hwpoison_filter_task(struct page *p)
  {

  	if (!hwpoison_filter_memcg)
  		return 0;

  	if (page_cgroup_ino(p) != 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);

  /*

   * 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;
  	short size_shift;

  };
  
  /*

   * Send all the processes who have the page mapped a signal.
   * ``action optional'' if they are not immediately affected by the error
   * ``action required'' if error happened in current execution context

   */

  static int kill_proc(struct to_kill *tk, unsigned long pfn, int flags)

  {

  	struct task_struct *t = tk->tsk;
  	short addr_lsb = tk->size_shift;

  	int ret = 0;

  	pr_err("Memory failure: %#lx: Sending SIGBUS to %s:%d due to hardware memory corruption
  ",

  			pfn, t->comm, t->pid);

  	if (flags & MF_ACTION_REQUIRED) {

  		WARN_ON_ONCE(t != current);
  		ret = force_sig_mceerr(BUS_MCEERR_AR,

  					 (void __user *)tk->addr, addr_lsb);

  	} else {
  		/*
  		 * 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 no one will do that?
  		 */

  		ret = send_sig_mceerr(BUS_MCEERR_AO, (void __user *)tk->addr,

  				      addr_lsb, t);  /* synchronous? */

  	}

  	if (ret < 0)

  		pr_info("Memory failure: 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 (PageHuge(p))
  		return;

  	if (!PageSlab(p)) {
  		lru_add_drain_all();
  		if (PageLRU(p))
  			return;

  		drain_all_pages(page_zone(p));

  		if (PageLRU(p) || is_free_buddy_page(p))
  			return;
  	}

  	/*

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

  	 */

  	if (access)
  		drop_slab_node(page_to_nid(p));

  }
  EXPORT_SYMBOL_GPL(shake_page);

  static unsigned long dev_pagemap_mapping_shift(struct page *page,
  		struct vm_area_struct *vma)
  {
  	unsigned long address = vma_address(page, vma);
  	pgd_t *pgd;
  	p4d_t *p4d;
  	pud_t *pud;
  	pmd_t *pmd;
  	pte_t *pte;
  
  	pgd = pgd_offset(vma->vm_mm, address);
  	if (!pgd_present(*pgd))
  		return 0;
  	p4d = p4d_offset(pgd, address);
  	if (!p4d_present(*p4d))
  		return 0;
  	pud = pud_offset(p4d, address);
  	if (!pud_present(*pud))
  		return 0;
  	if (pud_devmap(*pud))
  		return PUD_SHIFT;
  	pmd = pmd_offset(pud, address);
  	if (!pmd_present(*pmd))
  		return 0;
  	if (pmd_devmap(*pmd))
  		return PMD_SHIFT;
  	pte = pte_offset_map(pmd, address);
  	if (!pte_present(*pte))
  		return 0;
  	if (pte_devmap(*pte))
  		return PAGE_SHIFT;
  	return 0;
  }

  
  /*
   * 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.

   */
  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 *tk;

  	tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC);
  	if (!tk) {
  		pr_err("Memory failure: Out of memory while machine check handling
  ");
  		return;

  	}

  	tk->addr = page_address_in_vma(p, vma);

  	if (is_zone_device_page(p))
  		tk->size_shift = dev_pagemap_mapping_shift(p, vma);
  	else

  		tk->size_shift = page_shift(compound_head(p));

  
  	/*

  	 * Send SIGKILL if "tk->addr == -EFAULT". Also, as
  	 * "tk->size_shift" is always non-zero for !is_zone_device_page(),
  	 * so "tk->size_shift == 0" effectively checks no mapping on
  	 * ZONE_DEVICE. Indeed, when a devdax page is mmapped N times
  	 * to a process' address space, it's possible not all N VMAs
  	 * contain mappings for the page, but at least one VMA does.
  	 * Only deliver SIGBUS with payload derived from the VMA that
  	 * has a mapping for the page.

  	 */

  	if (tk->addr == -EFAULT) {

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

  			page_to_pfn(p), tsk->comm);

  	} else if (tk->size_shift == 0) {
  		kfree(tk);
  		return;

  	}

  	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(struct list_head *to_kill, int forcekill, bool fail,
  		unsigned long pfn, int flags)

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

  		if (forcekill) {

  			/*

  			 * 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 == -EFAULT) {

  				pr_err("Memory failure: %#lx: forcibly killing %s:%d because of failure to unmap corrupted page
  ",

  				       pfn, tk->tsk->comm, tk->tsk->pid);

  				do_send_sig_info(SIGKILL, SEND_SIG_PRIV,
  						 tk->tsk, PIDTYPE_PID);

  			}
  
  			/*
  			 * 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(tk, pfn, flags) < 0)

  				pr_err("Memory failure: %#lx: Cannot send advisory machine check signal to %s:%d
  ",

  				       pfn, tk->tsk->comm, tk->tsk->pid);

  		}
  		put_task_struct(tk->tsk);
  		kfree(tk);
  	}
  }

  /*
   * Find a dedicated thread which is supposed to handle SIGBUS(BUS_MCEERR_AO)
   * on behalf of the thread group. Return task_struct of the (first found)
   * dedicated thread if found, and return NULL otherwise.
   *
   * We already hold read_lock(&tasklist_lock) in the caller, so we don't
   * have to call rcu_read_lock/unlock() in this function.
   */
  static struct task_struct *find_early_kill_thread(struct task_struct *tsk)

  {

  	struct task_struct *t;

  	for_each_thread(tsk, t) {
  		if (t->flags & PF_MCE_PROCESS) {
  			if (t->flags & PF_MCE_EARLY)
  				return t;
  		} else {
  			if (sysctl_memory_failure_early_kill)
  				return t;
  		}
  	}

  	return NULL;
  }
  
  /*
   * Determine whether a given process is "early kill" process which expects
   * to be signaled when some page under the process is hwpoisoned.
   * Return task_struct of the dedicated thread (main thread unless explicitly
   * specified) if the process is "early kill," and otherwise returns NULL.

   *
   * Note that the above is true for Action Optional case, but not for Action
   * Required case where SIGBUS should sent only to the current thread.

   */
  static struct task_struct *task_early_kill(struct task_struct *tsk,
  					   int force_early)
  {

  	if (!tsk->mm)

  		return NULL;

  	if (force_early) {
  		/*
  		 * Comparing ->mm here because current task might represent
  		 * a subthread, while tsk always points to the main thread.
  		 */
  		if (tsk->mm == current->mm)
  			return current;
  		else
  			return NULL;
  	}

  	return find_early_kill_thread(tsk);

  }
  
  /*
   * Collect processes when the error hit an anonymous page.
   */
  static void collect_procs_anon(struct page *page, struct list_head *to_kill,

  				int force_early)

  {
  	struct vm_area_struct *vma;
  	struct task_struct *tsk;
  	struct anon_vma *av;

  	pgoff_t pgoff;

  	av = page_lock_anon_vma_read(page);

  	if (av == NULL)	/* Not actually mapped anymore */

  		return;

  	pgoff = page_to_pgoff(page);

  	read_lock(&tasklist_lock);

  	for_each_process (tsk) {

  		struct anon_vma_chain *vmac;

  		struct task_struct *t = task_early_kill(tsk, force_early);

  		if (!t)

  			continue;

  		anon_vma_interval_tree_foreach(vmac, &av->rb_root,
  					       pgoff, pgoff) {

  			vma = vmac->vma;

  			if (!page_mapped_in_vma(page, vma))
  				continue;

  			if (vma->vm_mm == t->mm)

  				add_to_kill(t, page, vma, to_kill);

  		}
  	}

  	read_unlock(&tasklist_lock);

  	page_unlock_anon_vma_read(av);

  }
  
  /*
   * Collect processes when the error hit a file mapped page.
   */
  static void collect_procs_file(struct page *page, struct list_head *to_kill,

  				int force_early)

  {
  	struct vm_area_struct *vma;
  	struct task_struct *tsk;

  	struct address_space *mapping = page->mapping;

  	pgoff_t pgoff;

  	i_mmap_lock_read(mapping);

  	read_lock(&tasklist_lock);

  	pgoff = page_to_pgoff(page);

  	for_each_process(tsk) {

  		struct task_struct *t = task_early_kill(tsk, force_early);

  		if (!t)

  			continue;

  		vma_interval_tree_foreach(vma, &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 == t->mm)

  				add_to_kill(t, page, vma, to_kill);

  		}
  	}

  	read_unlock(&tasklist_lock);

  	i_mmap_unlock_read(mapping);

  }
  
  /*
   * Collect the processes who have the corrupted page mapped to kill.

   */

  static void collect_procs(struct page *page, struct list_head *tokill,
  				int force_early)

  {

  	if (!page->mapping)
  		return;

  	if (PageAnon(page))

  		collect_procs_anon(page, tokill, force_early);

  	else

  		collect_procs_file(page, tokill, force_early);

  }

  static const char *action_name[] = {

  	[MF_IGNORED] = "Ignored",
  	[MF_FAILED] = "Failed",
  	[MF_DELAYED] = "Delayed",
  	[MF_RECOVERED] = "Recovered",

  };
  
  static const char * const action_page_types[] = {

  	[MF_MSG_KERNEL]			= "reserved kernel page",
  	[MF_MSG_KERNEL_HIGH_ORDER]	= "high-order kernel page",
  	[MF_MSG_SLAB]			= "kernel slab page",
  	[MF_MSG_DIFFERENT_COMPOUND]	= "different compound page after locking",
  	[MF_MSG_POISONED_HUGE]		= "huge page already hardware poisoned",
  	[MF_MSG_HUGE]			= "huge page",
  	[MF_MSG_FREE_HUGE]		= "free huge page",

  	[MF_MSG_NON_PMD_HUGE]		= "non-pmd-sized huge page",

  	[MF_MSG_UNMAP_FAILED]		= "unmapping failed page",
  	[MF_MSG_DIRTY_SWAPCACHE]	= "dirty swapcache page",
  	[MF_MSG_CLEAN_SWAPCACHE]	= "clean swapcache page",
  	[MF_MSG_DIRTY_MLOCKED_LRU]	= "dirty mlocked LRU page",
  	[MF_MSG_CLEAN_MLOCKED_LRU]	= "clean mlocked LRU page",
  	[MF_MSG_DIRTY_UNEVICTABLE_LRU]	= "dirty unevictable LRU page",
  	[MF_MSG_CLEAN_UNEVICTABLE_LRU]	= "clean unevictable LRU page",
  	[MF_MSG_DIRTY_LRU]		= "dirty LRU page",
  	[MF_MSG_CLEAN_LRU]		= "clean LRU page",
  	[MF_MSG_TRUNCATED_LRU]		= "already truncated LRU page",
  	[MF_MSG_BUDDY]			= "free buddy page",
  	[MF_MSG_BUDDY_2ND]		= "free buddy page (2nd try)",

  	[MF_MSG_DAX]			= "dax page",

  	[MF_MSG_UNSPLIT_THP]		= "unsplit thp",

  	[MF_MSG_UNKNOWN]		= "unknown page",

  };

  /*

   * 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);

  
  		/*
  		 * Poisoned page might never drop its ref count to 0 so we have
  		 * to uncharge it manually from its memcg.
  		 */
  		mem_cgroup_uncharge(p);

  		/*
  		 * drop the page count elevated by isolate_lru_page()
  		 */

  		put_page(p);

  		return 0;
  	}
  	return -EIO;
  }

  static int truncate_error_page(struct page *p, unsigned long pfn,
  				struct address_space *mapping)
  {
  	int ret = MF_FAILED;
  
  	if (mapping->a_ops->error_remove_page) {
  		int err = mapping->a_ops->error_remove_page(mapping, p);
  
  		if (err != 0) {
  			pr_info("Memory failure: %#lx: Failed to punch page: %d
  ",
  				pfn, err);
  		} else if (page_has_private(p) &&
  			   !try_to_release_page(p, GFP_NOIO)) {
  			pr_info("Memory failure: %#lx: failed to release buffers
  ",
  				pfn);
  		} else {
  			ret = MF_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 = MF_RECOVERED;
  		else
  			pr_info("Memory failure: %#lx: Failed to invalidate
  ",
  				pfn);
  	}
  
  	return ret;
  }

  /*

   * 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 MF_IGNORED;

  }
  
  /*
   * Page in unknown state. Do nothing.
   */
  static int me_unknown(struct page *p, unsigned long pfn)
  {

  	pr_err("Memory failure: %#lx: Unknown page state
  ", pfn);

  	return MF_FAILED;

  }
  
  /*

   * Clean (or cleaned) page cache page.
   */
  static int me_pagecache_clean(struct page *p, unsigned long pfn)
  {

  	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 MF_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 MF_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.
  	 */

  	return truncate_error_page(p, pfn, mapping);

  }
  
  /*

   * Dirty pagecache 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 between 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 MF_DELAYED;

  	else

  		return MF_FAILED;

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

  	delete_from_swap_cache(p);

  	if (!delete_from_lru_cache(p))

  		return MF_RECOVERED;

  	else

  		return MF_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);

  	struct address_space *mapping;

  
  	if (!PageHuge(hpage))
  		return MF_DELAYED;

  	mapping = page_mapping(hpage);
  	if (mapping) {
  		res = truncate_error_page(hpage, pfn, mapping);
  	} else {
  		unlock_page(hpage);
  		/*
  		 * migration entry prevents later access on error anonymous
  		 * hugepage, so we can free and dissolve it into buddy to
  		 * save healthy subpages.
  		 */
  		if (PageAnon(hpage))
  			put_page(hpage);
  		dissolve_free_huge_page(p);
  		res = MF_RECOVERED;
  		lock_page(hpage);

  	}

  
  	return res;

  }
  
  /*
   * 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 extremely 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) | (1UL << PG_swapbacked))

  #define unevict		(1UL << PG_unevictable)
  #define mlock		(1UL << PG_mlocked)

  #define lru		(1UL << PG_lru)

  #define head		(1UL << PG_head)

  #define slab		(1UL << PG_slab)

  #define reserved	(1UL << PG_reserved)
  
  static struct page_state {
  	unsigned long mask;
  	unsigned long res;

  	enum mf_action_page_type type;

  	int (*action)(struct page *p, unsigned long pfn);
  } error_states[] = {

  	{ reserved,	reserved,	MF_MSG_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,		MF_MSG_SLAB,	me_kernel },

  	{ head,		head,		MF_MSG_HUGE,		me_huge_page },

  	{ sc|dirty,	sc|dirty,	MF_MSG_DIRTY_SWAPCACHE,	me_swapcache_dirty },
  	{ sc|dirty,	sc,		MF_MSG_CLEAN_SWAPCACHE,	me_swapcache_clean },

  	{ mlock|dirty,	mlock|dirty,	MF_MSG_DIRTY_MLOCKED_LRU,	me_pagecache_dirty },
  	{ mlock|dirty,	mlock,		MF_MSG_CLEAN_MLOCKED_LRU,	me_pagecache_clean },

  	{ unevict|dirty, unevict|dirty,	MF_MSG_DIRTY_UNEVICTABLE_LRU,	me_pagecache_dirty },
  	{ unevict|dirty, unevict,	MF_MSG_CLEAN_UNEVICTABLE_LRU,	me_pagecache_clean },

  	{ lru|dirty,	lru|dirty,	MF_MSG_DIRTY_LRU,	me_pagecache_dirty },
  	{ lru|dirty,	lru,		MF_MSG_CLEAN_LRU,	me_pagecache_clean },

  
  	/*
  	 * Catchall entry: must be at end.
  	 */

  	{ 0,		0,		MF_MSG_UNKNOWN,	me_unknown },

  };

  #undef dirty
  #undef sc
  #undef unevict
  #undef mlock

  #undef lru

  #undef head

  #undef slab
  #undef reserved

  /*
   * "Dirty/Clean" indication is not 100% accurate due to the possibility of
   * setting PG_dirty outside page lock. See also comment above set_page_dirty().
   */

  static void action_result(unsigned long pfn, enum mf_action_page_type type,
  			  enum mf_result result)

  {

  	trace_memory_failure_event(pfn, type, result);

  	pr_err("Memory failure: %#lx: recovery action for %s: %s
  ",

  		pfn, action_page_types[type], 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);

  	count = page_count(p) - 1;

  	if (ps->action == me_swapcache_dirty && result == MF_DELAYED)

  		count--;

  	if (count > 0) {

  		pr_err("Memory failure: %#lx: %s still referenced by %d users
  ",

  		       pfn, action_page_types[ps->type], count);

  		result = MF_FAILED;

  	}

  	action_result(pfn, ps->type, result);

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

  	return (result == MF_RECOVERED || result == MF_DELAYED) ? 0 : -EBUSY;

  }

  /**
   * get_hwpoison_page() - Get refcount for memory error handling:
   * @page:	raw error page (hit by memory error)
   *
   * Return: return 0 if failed to grab the refcount, otherwise true (some
   * non-zero value.)
   */

  static int get_hwpoison_page(struct page *page)

  {
  	struct page *head = compound_head(page);

  	if (!PageHuge(head) && PageTransHuge(head)) {

  		/*
  		 * Non anonymous thp exists only in allocation/free time. We
  		 * can't handle such a case correctly, so let's give it up.
  		 * This should be better than triggering BUG_ON when kernel
  		 * tries to touch the "partially handled" page.
  		 */
  		if (!PageAnon(head)) {

  			pr_err("Memory failure: %#lx: non anonymous thp
  ",

  				page_to_pfn(page));
  			return 0;
  		}

  	}

  	if (get_page_unless_zero(head)) {
  		if (head == compound_head(page))
  			return 1;

  		pr_info("Memory failure: %#lx cannot catch tail
  ",
  			page_to_pfn(page));

  		put_page(head);
  	}
  
  	return 0;

  }

  /*
   * 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 bool hwpoison_user_mappings(struct page *p, unsigned long pfn,

  				  int flags, struct page **hpagep)

  {

  	enum ttu_flags ttu = TTU_IGNORE_MLOCK;

  	struct address_space *mapping;
  	LIST_HEAD(tokill);

  	bool unmap_success = true;

  	int kill = 1, forcekill;

  	struct page *hpage = *hpagep;

  	bool mlocked = PageMlocked(hpage);

  	/*
  	 * Here we are interested only in user-mapped pages, so skip any
  	 * other types of pages.
  	 */
  	if (PageReserved(p) || PageSlab(p))

  		return true;

  	if (!(PageLRU(hpage) || PageHuge(p)))

  		return true;

  	/*
  	 * 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 true;

  	if (PageKsm(p)) {

  		pr_err("Memory failure: %#lx: can't handle KSM pages.
  ", pfn);

  		return false;

  	}

  
  	if (PageSwapCache(p)) {

  		pr_err("Memory failure: %#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 (!(flags & MF_MUST_KILL) && !PageDirty(hpage) && mapping &&

  	    mapping_can_writeback(mapping)) {

  		if (page_mkclean(hpage)) {
  			SetPageDirty(hpage);

  		} else {
  			kill = 0;
  			ttu |= TTU_IGNORE_HWPOISON;

  			pr_info("Memory failure: %#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, flags & MF_ACTION_REQUIRED);

  	if (!PageHuge(hpage)) {
  		unmap_success = try_to_unmap(hpage, ttu);
  	} else {

  		if (!PageAnon(hpage)) {
  			/*
  			 * For hugetlb pages in shared mappings, try_to_unmap
  			 * could potentially call huge_pmd_unshare.  Because of
  			 * this, take semaphore in write mode here and set
  			 * TTU_RMAP_LOCKED to indicate we have taken the lock
  			 * at this higer level.
  			 */
  			mapping = hugetlb_page_mapping_lock_write(hpage);
  			if (mapping) {
  				unmap_success = try_to_unmap(hpage,

  						     ttu|TTU_RMAP_LOCKED);

  				i_mmap_unlock_write(mapping);
  			} else {
  				pr_info("Memory failure: %#lx: could not lock mapping for mapped huge page
  ", pfn);
  				unmap_success = false;
  			}

  		} else {

  			unmap_success = try_to_unmap(hpage, ttu);

  		}
  	}

  	if (!unmap_success)

  		pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)
  ",

  		       pfn, page_mapcount(hpage));

  	/*

  	 * try_to_unmap() might put mlocked page in lru cache, so call
  	 * shake_page() again to ensure that it's flushed.
  	 */
  	if (mlocked)
  		shake_page(hpage, 0);
  
  	/*

  	 * 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 or the process is not restartable,
  	 * 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.
  	 */

  	forcekill = PageDirty(hpage) || (flags & MF_MUST_KILL);

  	kill_procs(&tokill, forcekill, !unmap_success, pfn, flags);

  	return unmap_success;

  }

  static int identify_page_state(unsigned long pfn, struct page *p,
  				unsigned long page_flags)

  {
  	struct page_state *ps;

  
  	/*
  	 * The first check uses the current page flags which may not have any
  	 * relevant information. The second check with the saved page flags is
  	 * carried out only if the first check can't determine the page status.
  	 */
  	for (ps = error_states;; ps++)
  		if ((p->flags & ps->mask) == ps->res)
  			break;
  
  	page_flags |= (p->flags & (1UL << PG_dirty));
  
  	if (!ps->mask)
  		for (ps = error_states;; ps++)
  			if ((page_flags & ps->mask) == ps->res)
  				break;
  	return page_action(ps, p, pfn);
  }

  static int try_to_split_thp_page(struct page *page, const char *msg)
  {
  	lock_page(page);
  	if (!PageAnon(page) || unlikely(split_huge_page(page))) {
  		unsigned long pfn = page_to_pfn(page);
  
  		unlock_page(page);
  		if (!PageAnon(page))
  			pr_info("%s: %#lx: non anonymous thp
  ", msg, pfn);
  		else
  			pr_info("%s: %#lx: thp split failed
  ", msg, pfn);
  		put_page(page);
  		return -EBUSY;
  	}
  	unlock_page(page);
  
  	return 0;
  }

  static int memory_failure_hugetlb(unsigned long pfn, int flags)

  {

  	struct page *p = pfn_to_page(pfn);
  	struct page *head = compound_head(p);
  	int res;
  	unsigned long page_flags;
  
  	if (TestSetPageHWPoison(head)) {
  		pr_err("Memory failure: %#lx: already hardware poisoned
  ",
  		       pfn);
  		return 0;
  	}
  
  	num_poisoned_pages_inc();
  
  	if (!(flags & MF_COUNT_INCREASED) && !get_hwpoison_page(p)) {
  		/*
  		 * Check "filter hit" and "race with other subpage."
  		 */
  		lock_page(head);
  		if (PageHWPoison(head)) {
  			if ((hwpoison_filter(p) && TestClearPageHWPoison(p))
  			    || (p != head && TestSetPageHWPoison(head))) {
  				num_poisoned_pages_dec();
  				unlock_page(head);
  				return 0;
  			}
  		}
  		unlock_page(head);
  		dissolve_free_huge_page(p);
  		action_result(pfn, MF_MSG_FREE_HUGE, MF_DELAYED);
  		return 0;
  	}
  
  	lock_page(head);
  	page_flags = head->flags;
  
  	if (!PageHWPoison(head)) {
  		pr_err("Memory failure: %#lx: just unpoisoned
  ", pfn);
  		num_poisoned_pages_dec();
  		unlock_page(head);

  		put_page(head);

  		return 0;
  	}

  	/*
  	 * TODO: hwpoison for pud-sized hugetlb doesn't work right now, so
  	 * simply disable it. In order to make it work properly, we need
  	 * make sure that:
  	 *  - conversion of a pud that maps an error hugetlb into hwpoison
  	 *    entry properly works, and
  	 *  - other mm code walking over page table is aware of pud-aligned
  	 *    hwpoison entries.
  	 */
  	if (huge_page_size(page_hstate(head)) > PMD_SIZE) {
  		action_result(pfn, MF_MSG_NON_PMD_HUGE, MF_IGNORED);
  		res = -EBUSY;
  		goto out;
  	}

  	if (!hwpoison_user_mappings(p, pfn, flags, &head)) {

  		action_result(pfn, MF_MSG_UNMAP_FAILED, MF_IGNORED);
  		res = -EBUSY;
  		goto out;
  	}

  	res = identify_page_state(pfn, p, page_flags);

  out:
  	unlock_page(head);
  	return res;
  }

  static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
  		struct dev_pagemap *pgmap)
  {
  	struct page *page = pfn_to_page(pfn);
  	const bool unmap_success = true;
  	unsigned long size = 0;
  	struct to_kill *tk;
  	LIST_HEAD(tokill);
  	int rc = -EBUSY;
  	loff_t start;

  	dax_entry_t cookie;

  	if (flags & MF_COUNT_INCREASED)
  		/*
  		 * Drop the extra refcount in case we come from madvise().
  		 */
  		put_page(page);

  	/*
  	 * Prevent the inode from being freed while we are interrogating
  	 * the address_space, typically this would be handled by
  	 * lock_page(), but dax pages do not use the page lock. This
  	 * also prevents changes to the mapping of this pfn until
  	 * poison signaling is complete.
  	 */

  	cookie = dax_lock_page(page);
  	if (!cookie)

  		goto out;
  
  	if (hwpoison_filter(page)) {
  		rc = 0;
  		goto unlock;
  	}

  	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {

  		/*
  		 * TODO: Handle HMM pages which may need coordination
  		 * with device-side memory.
  		 */
  		goto unlock;

  	}
  
  	/*
  	 * Use this flag as an indication that the dax page has been
  	 * remapped UC to prevent speculative consumption of poison.
  	 */
  	SetPageHWPoison(page);
  
  	/*
  	 * Unlike System-RAM there is no possibility to swap in a
  	 * different physical page at a given virtual address, so all
  	 * userspace consumption of ZONE_DEVICE memory necessitates
  	 * SIGBUS (i.e. MF_MUST_KILL)
  	 */
  	flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;
  	collect_procs(page, &tokill, flags & MF_ACTION_REQUIRED);
  
  	list_for_each_entry(tk, &tokill, nd)
  		if (tk->size_shift)
  			size = max(size, 1UL << tk->size_shift);
  	if (size) {
  		/*
  		 * Unmap the largest mapping to avoid breaking up
  		 * device-dax mappings which are constant size. The
  		 * actual size of the mapping being torn down is
  		 * communicated in siginfo, see kill_proc()
  		 */
  		start = (page->index << PAGE_SHIFT) & ~(size - 1);
  		unmap_mapping_range(page->mapping, start, start + size, 0);
  	}
  	kill_procs(&tokill, flags & MF_MUST_KILL, !unmap_success, pfn, flags);
  	rc = 0;
  unlock:

  	dax_unlock_page(page, cookie);

  out:
  	/* drop pgmap ref acquired in caller */
  	put_dev_pagemap(pgmap);
  	action_result(pfn, MF_MSG_DAX, rc ? MF_FAILED : MF_RECOVERED);
  	return rc;
  }

  /**
   * memory_failure - Handle memory failure of a page.
   * @pfn: Page Number of the corrupted page

   * @flags: fine tune action taken
   *
   * 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.
   */

  int memory_failure(unsigned long pfn, int flags)

  {

  	struct page *p;

  	struct page *hpage;

  	struct page *orig_head;

  	struct dev_pagemap *pgmap;

  	int res;

  	unsigned long page_flags;

  
  	if (!sysctl_memory_failure_recovery)

  		panic("Memory failure on page %lx", pfn);

  	p = pfn_to_online_page(pfn);
  	if (!p) {
  		if (pfn_valid(pfn)) {
  			pgmap = get_dev_pagemap(pfn, NULL);
  			if (pgmap)
  				return memory_failure_dev_pagemap(pfn, flags,
  								  pgmap);
  		}

  		pr_err("Memory failure: %#lx: memory outside kernel control
  ",
  			pfn);

  		return -ENXIO;

  	}

  	if (PageHuge(p))

  		return memory_failure_hugetlb(pfn, flags);

  	if (TestSetPageHWPoison(p)) {

  		pr_err("Memory failure: %#lx: already hardware poisoned
  ",
  			pfn);

  		return 0;
  	}

  	orig_head = hpage = compound_head(p);

  	num_poisoned_pages_inc();

  
  	/*
  	 * 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 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_ref_freeze()/page_ref_unfreeze() mismatch.

  	 */

  	if (!(flags & MF_COUNT_INCREASED) && !get_hwpoison_page(p)) {

  		if (is_free_buddy_page(p)) {

  			action_result(pfn, MF_MSG_BUDDY, MF_DELAYED);

  			return 0;
  		} else {

  			action_result(pfn, MF_MSG_KERNEL_HIGH_ORDER, MF_IGNORED);

  			return -EBUSY;
  		}

  	}

  	if (PageTransHuge(hpage)) {

  		if (try_to_split_thp_page(p, "Memory Failure") < 0) {
  			action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED);

  			return -EBUSY;

  		}

  		VM_BUG_ON_PAGE(!page_count(p), p);

  	}

  	/*

  	 * 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 __SetPageLocked()

  	 * - 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.
  	 */

  	shake_page(p, 0);
  	/* shake_page could have turned it free. */
  	if (!PageLRU(p) && is_free_buddy_page(p)) {
  		if (flags & MF_COUNT_INCREASED)
  			action_result(pfn, MF_MSG_BUDDY, MF_DELAYED);
  		else
  			action_result(pfn, MF_MSG_BUDDY_2ND, MF_DELAYED);
  		return 0;

  	}

  	lock_page(p);

  
  	/*

  	 * The page could have changed compound pages during the locking.
  	 * If this happens just bail out.
  	 */

  	if (PageCompound(p) && compound_head(p) != orig_head) {

  		action_result(pfn, MF_MSG_DIFFERENT_COMPOUND, MF_IGNORED);

  		res = -EBUSY;
  		goto out;
  	}
  
  	/*

  	 * We use page flags to determine what action should be taken, but
  	 * the flags can be modified by the error containment action.  One
  	 * example is an mlocked page, where PG_mlocked is cleared by
  	 * page_remove_rmap() in try_to_unmap_one(). So to determine page status
  	 * correctly, we save a copy of the page flags at this time.
  	 */

  	page_flags = p->flags;

  
  	/*

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

  		pr_err("Memory failure: %#lx: just unpoisoned
  ", pfn);

  		num_poisoned_pages_dec();

  		unlock_page(p);

  		put_page(p);

  		return 0;

  	}

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

  			num_poisoned_pages_dec();

  		unlock_page(p);

  		put_page(p);

  		return 0;
  	}

  	if (!PageTransTail(p) && !PageLRU(p))

  		goto identify_page_state;

  	/*

  	 * It's very difficult to mess with pages currently under IO
  	 * and in many cases impossible, so we just avoid it here.
  	 */

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

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

  	 */

  	if (!hwpoison_user_mappings(p, pfn, flags, &p)) {

  		action_result(pfn, MF_MSG_UNMAP_FAILED, MF_IGNORED);

  		res = -EBUSY;
  		goto out;
  	}

  
  	/*
  	 * Torn down by someone else?
  	 */

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

  		action_result(pfn, MF_MSG_TRUNCATED_LRU, MF_IGNORED);

  		res = -EBUSY;

  		goto out;
  	}

  identify_page_state:

  	res = identify_page_state(pfn, p, page_flags);

  out:

  	unlock_page(p);

  	return res;
  }

  EXPORT_SYMBOL_GPL(memory_failure);

  #define MEMORY_FAILURE_FIFO_ORDER	4
  #define MEMORY_FAILURE_FIFO_SIZE	(1 << MEMORY_FAILURE_FIFO_ORDER)
  
  struct memory_failure_entry {
  	unsigned long pfn;

  	int flags;
  };
  
  struct memory_failure_cpu {
  	DECLARE_KFIFO(fifo, struct memory_failure_entry,
  		      MEMORY_FAILURE_FIFO_SIZE);
  	spinlock_t lock;
  	struct work_struct work;
  };
  
  static DEFINE_PER_CPU(struct memory_failure_cpu, memory_failure_cpu);
  
  /**
   * memory_failure_queue - Schedule handling memory failure of a page.
   * @pfn: Page Number of the corrupted page

   * @flags: Flags for memory failure handling
   *
   * This function is called by the low level hardware error handler
   * when it detects hardware memory corruption of a page. It schedules
   * the recovering of error page, including 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)
   *
   * Can run in IRQ context.
   */

  void memory_failure_queue(unsigned long pfn, int flags)

  {
  	struct memory_failure_cpu *mf_cpu;
  	unsigned long proc_flags;
  	struct memory_failure_entry entry = {
  		.pfn =		pfn,

  		.flags =	flags,
  	};
  
  	mf_cpu = &get_cpu_var(memory_failure_cpu);
  	spin_lock_irqsave(&mf_cpu->lock, proc_flags);

  	if (kfifo_put(&mf_cpu->fifo, entry))

  		schedule_work_on(smp_processor_id(), &mf_cpu->work);
  	else

  		pr_err("Memory failure: buffer overflow when queuing memory failure at %#lx
  ",

  		       pfn);
  	spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
  	put_cpu_var(memory_failure_cpu);
  }
  EXPORT_SYMBOL_GPL(memory_failure_queue);
  
  static void memory_failure_work_func(struct work_struct *work)
  {
  	struct memory_failure_cpu *mf_cpu;
  	struct memory_failure_entry entry = { 0, };
  	unsigned long proc_flags;
  	int gotten;

  	mf_cpu = container_of(work, struct memory_failure_cpu, work);

  	for (;;) {
  		spin_lock_irqsave(&mf_cpu->lock, proc_flags);
  		gotten = kfifo_get(&mf_cpu->fifo, &entry);
  		spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
  		if (!gotten)
  			break;

  		if (entry.flags & MF_SOFT_OFFLINE)

  			soft_offline_page(entry.pfn, entry.flags);

  		else

  			memory_failure(entry.pfn, entry.flags);

  	}
  }

  /*
   * Process memory_failure work queued on the specified CPU.
   * Used to avoid return-to-userspace racing with the memory_failure workqueue.
   */
  void memory_failure_queue_kick(int cpu)
  {
  	struct memory_failure_cpu *mf_cpu;
  
  	mf_cpu = &per_cpu(memory_failure_cpu, cpu);
  	cancel_work_sync(&mf_cpu->work);
  	memory_failure_work_func(&mf_cpu->work);
  }

  static int __init memory_failure_init(void)
  {
  	struct memory_failure_cpu *mf_cpu;
  	int cpu;
  
  	for_each_possible_cpu(cpu) {
  		mf_cpu = &per_cpu(memory_failure_cpu, cpu);
  		spin_lock_init(&mf_cpu->lock);
  		INIT_KFIFO(mf_cpu->fifo);
  		INIT_WORK(&mf_cpu->work, memory_failure_work_func);
  	}
  
  	return 0;
  }
  core_initcall(memory_failure_init);

  #define unpoison_pr_info(fmt, pfn, rs)			\
  ({							\
  	if (__ratelimit(rs))				\
  		pr_info(fmt, pfn);			\
  })

  /**
   * 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;

  	static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
  					DEFAULT_RATELIMIT_BURST);

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

  		unpoison_pr_info("Unpoison: Page was already unpoisoned %#lx
  ",

  				 pfn, &unpoison_rs);

  		return 0;
  	}

  	if (page_count(page) > 1) {

  		unpoison_pr_info("Unpoison: Someone grabs the hwpoison page %#lx
  ",

  				 pfn, &unpoison_rs);

  		return 0;
  	}
  
  	if (page_mapped(page)) {

  		unpoison_pr_info("Unpoison: Someone maps the hwpoison page %#lx
  ",

  				 pfn, &unpoison_rs);

  		return 0;
  	}
  
  	if (page_mapping(page)) {

  		unpoison_pr_info("Unpoison: the hwpoison page has non-NULL mapping %#lx
  ",

  				 pfn, &unpoison_rs);

  		return 0;
  	}

  	/*
  	 * unpoison_memory() can encounter thp only when the thp is being
  	 * worked by memory_failure() and the page lock is not held yet.
  	 * In such case, we yield to memory_failure() and make unpoison fail.
  	 */

  	if (!PageHuge(page) && PageTransHuge(page)) {

  		unpoison_pr_info("Unpoison: Memory failure is now running on %#lx
  ",

  				 pfn, &unpoison_rs);

  		return 0;

  	}

  	if (!get_hwpoison_page(p)) {

  		if (TestClearPageHWPoison(p))

  			num_poisoned_pages_dec();

  		unpoison_pr_info("Unpoison: Software-unpoisoned free page %#lx
  ",

  				 pfn, &unpoison_rs);

  		return 0;
  	}

  	lock_page(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)) {

  		unpoison_pr_info("Unpoison: Software-unpoisoned page %#lx
  ",

  				 pfn, &unpoison_rs);

  		num_poisoned_pages_dec();

  		freeit = 1;
  	}
  	unlock_page(page);

  	put_page(page);

  	if (freeit && !(pfn == my_zero_pfn(0) && page_count(p) == 1))

  		put_page(page);

  
  	return 0;
  }
  EXPORT_SYMBOL(unpoison_memory);

  /*
   * 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;
  
  	/*

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

  	if (!get_hwpoison_page(p)) {

  		if (PageHuge(p)) {

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

  			ret = 0;

  		} else if (is_free_buddy_page(p)) {

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

  			ret = 0;

  		} else if (page_count(p)) {
  			/* raced with allocation */
  			ret = -EBUSY;

  		} else {

  			pr_info("%s: %#lx: unknown zero refcount page type %lx
  ",
  				__func__, pfn, p->flags);

  			ret = -EIO;
  		}
  	} else {
  		/* Not a free page */
  		ret = 1;
  	}

  	return ret;
  }

  static int get_any_page(struct page *page, unsigned long pfn, int flags)
  {
  	int ret = __get_any_page(page, pfn, flags);

  	if (ret == -EBUSY)
  		ret = __get_any_page(page, pfn, flags);

  	if (ret == 1 && !PageHuge(page) &&
  	    !PageLRU(page) && !__PageMovable(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 == 1 && !PageLRU(page)) {

  			/* Drop page reference which is from __get_any_page() */

  			put_page(page);

  			pr_info("soft_offline: %#lx: unknown non LRU page type %lx (%pGp)
  ",
  				pfn, page->flags, &page->flags);

  			return -EIO;
  		}
  	}
  	return ret;
  }

  static bool isolate_page(struct page *page, struct list_head *pagelist)

  {

  	bool isolated = false;
  	bool lru = PageLRU(page);

  	if (PageHuge(page)) {
  		isolated = isolate_huge_page(page, pagelist);
  	} else {
  		if (lru)
  			isolated = !isolate_lru_page(page);
  		else
  			isolated = !isolate_movable_page(page, ISOLATE_UNEVICTABLE);
  
  		if (isolated)
  			list_add(&page->lru, pagelist);

  	}

  	if (isolated && lru)
  		inc_node_page_state(page, NR_ISOLATED_ANON +
  				    page_is_file_lru(page));

  	/*

  	 * If we succeed to isolate the page, we grabbed another refcount on
  	 * the page, so we can safely drop the one we got from get_any_pages().
  	 * If we failed to isolate the page, it means that we cannot go further
  	 * and we will return an error, so drop the reference we got from
  	 * get_any_pages() as well.

  	 */

  	put_page(page);
  	return isolated;

  }

  /*
   * __soft_offline_page handles hugetlb-pages and non-hugetlb pages.
   * If the page is a non-dirty unmapped page-cache page, it simply invalidates.
   * If the page is mapped, it migrates the contents over.
   */
  static int __soft_offline_page(struct page *page)

  {

  	int ret = 0;

  	unsigned long pfn = page_to_pfn(page);

  	struct page *hpage = compound_head(page);
  	char const *msg_page[] = {"page", "hugepage"};
  	bool huge = PageHuge(page);
  	LIST_HEAD(pagelist);

  	struct migration_target_control mtc = {
  		.nid = NUMA_NO_NODE,
  		.gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL,
  	};

  	/*

  	 * Check PageHWPoison again inside page lock because PageHWPoison
  	 * is set by memory_failure() outside page lock. Note that
  	 * memory_failure() also double-checks PageHWPoison inside page lock,
  	 * so there's no race between soft_offline_page() and memory_failure().

  	 */

  	lock_page(page);

  	if (!PageHuge(page))
  		wait_on_page_writeback(page);

  	if (PageHWPoison(page)) {
  		unlock_page(page);

  		put_page(page);

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

  		return 0;

  	}

  
  	if (!PageHuge(page))
  		/*
  		 * Try to invalidate first. This should work for
  		 * non dirty unmapped page cache pages.
  		 */
  		ret = invalidate_inode_page(page);

  	unlock_page(page);

  	/*

  	 * RED-PEN would be better to keep it isolated here, but we
  	 * would need to fix isolation locking first.
  	 */

  	if (ret) {

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

  		page_handle_poison(page, false, true);

  		return 0;

  	}

  	if (isolate_page(hpage, &pagelist)) {

  		ret = migrate_pages(&pagelist, alloc_migration_target, NULL,
  			(unsigned long)&mtc, MIGRATE_SYNC, MR_MEMORY_FAILURE);

  		if (!ret) {

  			bool release = !huge;
  
  			if (!page_handle_poison(page, huge, release))
  				ret = -EBUSY;

  		} else {

  			if (!list_empty(&pagelist))
  				putback_movable_pages(&pagelist);

  			pr_info("soft offline: %#lx: %s migration failed %d, type %lx (%pGp)
  ",
  				pfn, msg_page[huge], ret, page->flags, &page->flags);

  			if (ret > 0)
  				ret = -EIO;
  		}
  	} else {

  		pr_info("soft offline: %#lx: %s isolation failed: %d, page count %d, type %lx (%pGp)
  ",
  			pfn, msg_page[huge], ret, page_count(page), page->flags, &page->flags);
  		ret = -EBUSY;

  	}

  	return ret;
  }

  static int soft_offline_in_use_page(struct page *page)

  {

  	struct page *hpage = compound_head(page);

  	if (!PageHuge(page) && PageTransHuge(hpage))
  		if (try_to_split_thp_page(page, "soft offline") < 0)