Merge branch 'hwpoison-2.6.32' of git://git.kernel.org/pub/scm/linux/kernel/git/ak/linux-mce-2.6

What is hwpoison?

Upcoming Intel CPUs have support for recovering from some memory errors

(``MCA recovery''). This requires the OS to declare a page "poisoned",

kill the processes associated with it and avoid using it in the future.

This patchkit implements the necessary infrastructure in the VM.

To quote the overview comment:

 * High level machine check handler. Handles pages reported by the

 * hardware as being corrupted usually due to a 2bit ECC memory or cache

 * failure.

 *

 * This focusses on pages detected as corrupted in the background.

 * When the current CPU tries to consume corruption the currently

 * running process can just be killed directly instead. This implies

 * that if the error cannot be handled for some reason it's safe to

 * just ignore it because no corruption has been consumed yet. Instead

 * when that happens another machine check will happen.

 *

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

 * here is that we can access any page asynchronous to other VM

 * users, because memory failures could happen anytime and anywhere,

 * possibly violating 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.

 *

 * Some of the operations here are somewhat inefficient and have non

 * linear algorithmic complexity, because the data structures have not

 * been optimized for this case. This is in particular the case

 * for the mapping from a vma to a process. Since this case is expected

 * to be rare we hope we can get away with this.

The code consists of a the high level handler in mm/memory-failure.c,

a new page poison bit and various checks in the VM to handle poisoned

pages.

The main target right now is KVM guests, but it works for all kinds

of applications. KVM support requires a recent qemu-kvm release.

For the KVM use there was need for a new signal type so that

KVM can inject the machine check into the guest with the proper

address. This in theory allows other applications to handle

memory failures too. The expection is that near all applications

won't do that, but some very specialized ones might.

---

There are two (actually three) modi memory failure recovery can be in:

vm.memory_failure_recovery sysctl set to zero:

	All memory failures cause a panic. Do not attempt recovery.

	(on x86 this can be also affected by the tolerant level of the

	MCE subsystem)

early kill

	(can be controlled globally and per process)

	Send SIGBUS to the application as soon as the error is detected

	This allows applications who can process memory errors in a gentle

	way (e.g. drop affected object)

	This is the mode used by KVM qemu.

late kill

	Send SIGBUS when the application runs into the corrupted page.

	This is best for memory error unaware applications and default

	Note some pages are always handled as late kill.

---

User control:

vm.memory_failure_recovery

	See sysctl.txt

vm.memory_failure_early_kill

	Enable early kill mode globally

PR_MCE_KILL

	Set early/late kill mode/revert to system default

	arg1: PR_MCE_KILL_CLEAR: Revert to system default

	arg1: PR_MCE_KILL_SET: arg2 defines thread specific mode

		PR_MCE_KILL_EARLY: Early kill

		PR_MCE_KILL_LATE:  Late kill

		PR_MCE_KILL_DEFAULT: Use system global default

PR_MCE_KILL_GET

	return current mode

---

Testing:

madvise(MADV_POISON, ....)

	(as root)

	Poison a page in the process for testing

hwpoison-inject module through debugfs

	/sys/debug/hwpoison/corrupt-pfn

Inject hwpoison fault at PFN echoed into this file

Architecture specific MCE injector

x86 has mce-inject, mce-test

Some portable hwpoison test programs in mce-test, see blow.

---

References:

http://halobates.de/mce-lc09-2.pdf

	Overview presentation from LinuxCon 09

git://git.kernel.org/pub/scm/utils/cpu/mce/mce-test.git

	Test suite (hwpoison specific portable tests in tsrc)

git://git.kernel.org/pub/scm/utils/cpu/mce/mce-inject.git

	x86 specific injector

---

Limitations:

- Not all page types are supported and never will. Most kernel internal

objects cannot be recovered, only LRU pages for now.

- Right now hugepage support is missing.

---

Andi Kleen, Oct 2009

#define PR_TASK_PERF_EVENTS_DISABLE		31

#define PR_TASK_PERF_EVENTS_ENABLE		32

/*

 * Set early/late kill mode for hwpoison memory corruption.

 * This influences when the process gets killed on a memory corruption.

 */

#define PR_MCE_KILL	33

# define PR_MCE_KILL_CLEAR   0

# define PR_MCE_KILL_SET     1

# define PR_MCE_KILL_LATE    0

# define PR_MCE_KILL_EARLY   1

# define PR_MCE_KILL_DEFAULT 2

#define PR_MCE_KILL_GET 34

#endif /* _LINUX_PRCTL_H */

			if (arg4 | arg5)

				return -EINVAL;

			switch (arg2) {

			case 0:

			case PR_MCE_KILL_CLEAR:

				if (arg3 != 0)

					return -EINVAL;

				current->flags &= ~PF_MCE_PROCESS;

				break;

			case 1:

			case PR_MCE_KILL_SET:

				current->flags |= PF_MCE_PROCESS;

				if (arg3 != 0)

				if (arg3 == PR_MCE_KILL_EARLY)

					current->flags |= PF_MCE_EARLY;

				else

				else if (arg3 == PR_MCE_KILL_LATE)

					current->flags &= ~PF_MCE_EARLY;

				else if (arg3 == PR_MCE_KILL_DEFAULT)

					current->flags &=

						~(PF_MCE_EARLY|PF_MCE_PROCESS);

				else

					return -EINVAL;

				break;

			default:

				return -EINVAL;

			}

			error = 0;

			break;

		case PR_MCE_KILL_GET:

			if (arg2 | arg3 | arg4 | arg5)

				return -EINVAL;

			if (current->flags & PF_MCE_PROCESS)

				error = (current->flags & PF_MCE_EARLY) ?

					PR_MCE_KILL_EARLY : PR_MCE_KILL_LATE;

			else

				error = PR_MCE_KILL_DEFAULT;

			break;

		default:

			error = -EINVAL;

			break;

int schedule_on_each_cpu(work_func_t func)

{

	int cpu;

	int orig = -1;

	struct work_struct *works;

	works = alloc_percpu(struct work_struct);

	if (!works)

		return -ENOMEM;

	/*

	 * when running in keventd don't schedule a work item on itself.

	 * Can just call directly because the work queue is already bound.

	 * This also is faster.

	 * Make this a generic parameter for other workqueues?

	 */

	if (current_is_keventd()) {

		orig = raw_smp_processor_id();

		INIT_WORK(per_cpu_ptr(works, orig), func);

		func(per_cpu_ptr(works, orig));

	}

	get_online_cpus();

	for_each_online_cpu(cpu) {

		struct work_struct *work = per_cpu_ptr(works, cpu);

		if (cpu == orig)

			continue;

		INIT_WORK(work, func);

		schedule_work_on(cpu, work);

	}

	for_each_online_cpu(cpu)

	for_each_online_cpu(cpu) {

		if (cpu != orig)

			flush_work(per_cpu_ptr(works, cpu));

	}

	put_online_cpus();

	free_percpu(works);

	return 0;

	int ret = FAILED;

	struct address_space *mapping;

	if (!isolate_lru_page(p))

		page_cache_release(p);

	/*

	 * For anonymous pages we're done the only reference left

	 * should be the one m_f() holds.

 */

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

{

	int ret = FAILED;

	ClearPageDirty(p);

	/* Trigger EIO in shmem: */

	ClearPageUptodate(p);

	if (!isolate_lru_page(p)) {

		page_cache_release(p);

		ret = DELAYED;

	}

	return ret;

	return DELAYED;

}

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

{

	int ret = FAILED;

	if (!isolate_lru_page(p)) {

		page_cache_release(p);

		ret = RECOVERED;

	}

	delete_from_swap_cache(p);

	return ret;

	return RECOVERED;

}

/*

	{ 0,		0,		"unknown page state",	me_unknown },

};

#undef lru

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

{

	struct page *page = NULL;

			unsigned long pfn, int ref)

{

	int result;

	int count;

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

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

	if (page_count(p) != 1 + ref)

	count = page_count(p) - 1 - ref;

	if (count != 0)

		printk(KERN_ERR

		       "MCE %#lx: %s page still referenced by %d users\n",

		       pfn, ps->msg, page_count(p) - 1);

		       pfn, ps->msg, count);

	/* Could do more checks here if page looks ok */

	/*

	if (PageReserved(p) || PageCompound(p) || PageSlab(p) || PageKsm(p))

		return;

	if (!PageLRU(p))

		lru_add_drain_all();

	/*

	 * This check implies we don't kill processes if their pages

	 * are in the swap cache early. Those are always late kills.

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

{

	unsigned long lru_flag;

	struct page_state *ps;

	struct page *p;

	int res;

		return PageBuddy(compound_head(p)) ? 0 : -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))

		lru_add_drain_all();

	lru_flag = p->flags & lru;

	if (isolate_lru_page(p)) {

		action_result(pfn, "non LRU", IGNORED);

		put_page(p);

		return -EBUSY;

	}

	page_cache_release(p);

	/*

	 * Lock the page and wait for writeback to finish.

	 * It's very difficult to mess with pages currently under IO

	/*

	 * Torn down by someone else?

	 */

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

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

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

		res = 0;

		goto out;

	res = -EBUSY;

	for (ps = error_states;; ps++) {

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

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

			res = page_action(ps, p, pfn, ref);

			break;

		}