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Commit 95d2ac4a authored by Daniel Kiper's avatar Daniel Kiper Committed by Konrad Rzeszutek Wilk
Browse files

xen/balloon: Protect against CPU exhaust by event/x process 



Protect against CPU exhaust by event/x process during
errors by adding some delays in scheduling next event
and retry count limit.

Signed-off-by: default avatarDaniel Kiper <dkiper@net-space.pl>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent 95170b2e

drivers/xen/balloon.c

+90 −17
Original line number Diff line number Diff line
@@ -66,6 +66,22 @@ 


#define BALLOON_CLASS_NAME "xen_memory"



/*

 * balloon_process() state:

 *

 * BP_DONE: done or nothing to do,

 * BP_EAGAIN: error, go to sleep,

 * BP_ECANCELED: error, balloon operation canceled.

 */



enum bp_state {

	BP_DONE,

	BP_EAGAIN,

	BP_ECANCELED

};



#define RETRY_UNLIMITED	0



struct balloon_stats {

	/* We aim for 'current allocation' == 'target allocation'. */

	unsigned long current_pages;
@@ -73,6 +89,10 @@ struct balloon_stats { 
	/* Number of pages in high- and low-memory balloons. */

	unsigned long balloon_low;

	unsigned long balloon_high;

	unsigned long schedule_delay;

	unsigned long max_schedule_delay;

	unsigned long retry_count;

	unsigned long max_retry_count;

};



static DEFINE_MUTEX(balloon_mutex);
@@ -171,6 +191,36 @@ static struct page *balloon_next_page(struct page *page) 
	return list_entry(next, struct page, lru);

}



static enum bp_state update_schedule(enum bp_state state)

{

	if (state == BP_DONE) {

		balloon_stats.schedule_delay = 1;

		balloon_stats.retry_count = 1;

		return BP_DONE;

	}



	pr_info("xen_balloon: Retry count: %lu/%lu\n", balloon_stats.retry_count,

			balloon_stats.max_retry_count);



	++balloon_stats.retry_count;



	if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&

			balloon_stats.retry_count > balloon_stats.max_retry_count) {

		pr_info("xen_balloon: Retry count limit exceeded\n"

			"xen_balloon: Balloon operation canceled\n");

		balloon_stats.schedule_delay = 1;

		balloon_stats.retry_count = 1;

		return BP_ECANCELED;

	}



	balloon_stats.schedule_delay <<= 1;



	if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)

		balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;



	return BP_EAGAIN;

}



static unsigned long current_target(void)

{

	unsigned long target = balloon_stats.target_pages;
@@ -183,11 +233,11 @@ static unsigned long current_target(void) 
	return target;

}



static int increase_reservation(unsigned long nr_pages)

static enum bp_state increase_reservation(unsigned long nr_pages)

{

	int rc;

	unsigned long  pfn, i;

	struct page   *page;

	long           rc;

	struct xen_memory_reservation reservation = {

		.address_bits = 0,

		.extent_order = 0,
@@ -199,7 +249,10 @@ static int increase_reservation(unsigned long nr_pages) 


	page = balloon_first_page();

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

		BUG_ON(page == NULL);

		if (!page) {

			nr_pages = i;

			break;

		}

		frame_list[i] = page_to_pfn(page);

		page = balloon_next_page(page);

	}
@@ -207,8 +260,10 @@ static int increase_reservation(unsigned long nr_pages) 
	set_xen_guest_handle(reservation.extent_start, frame_list);

	reservation.nr_extents = nr_pages;

	rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);

	if (rc < 0)

		goto out;

	if (rc <= 0) {

		pr_info("xen_balloon: %s: Cannot allocate memory\n", __func__);

		return BP_EAGAIN;

	}



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

		page = balloon_retrieve();
@@ -238,15 +293,14 @@ static int increase_reservation(unsigned long nr_pages) 


	balloon_stats.current_pages += rc;



 out:

	return rc < 0 ? rc : rc != nr_pages;

	return BP_DONE;

}



static int decrease_reservation(unsigned long nr_pages)

static enum bp_state decrease_reservation(unsigned long nr_pages)

{

	enum bp_state state = BP_DONE;

	unsigned long  pfn, i;

	struct page   *page;

	int            need_sleep = 0;

	int ret;

	struct xen_memory_reservation reservation = {

		.address_bits = 0,
@@ -259,8 +313,9 @@ static int decrease_reservation(unsigned long nr_pages) 


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

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

			pr_info("xen_balloon: %s: Cannot allocate memory\n", __func__);

			nr_pages = i;

			need_sleep = 1;

			state = BP_EAGAIN;

			break;

		}
@@ -296,7 +351,7 @@ static int decrease_reservation(unsigned long nr_pages) 


	balloon_stats.current_pages -= nr_pages;



	return need_sleep;

	return state;

}



/*
@@ -307,27 +362,31 @@ static int decrease_reservation(unsigned long nr_pages) 
 */

static void balloon_process(struct work_struct *work)

{

	int need_sleep = 0;

	enum bp_state state = BP_DONE;

	long credit;



	mutex_lock(&balloon_mutex);



	do {

		credit = current_target() - balloon_stats.current_pages;



		if (credit > 0)

			need_sleep = (increase_reservation(credit) != 0);

			state = increase_reservation(credit);



		if (credit < 0)

			need_sleep = (decrease_reservation(-credit) != 0);

			state = decrease_reservation(-credit);



		state = update_schedule(state);



#ifndef CONFIG_PREEMPT

		if (need_resched())

			schedule();

#endif

	} while ((credit != 0) && !need_sleep);

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



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

	if (current_target() != balloon_stats.current_pages)

		schedule_delayed_work(&balloon_worker, HZ);

	if (state == BP_EAGAIN)

		schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);



	mutex_unlock(&balloon_mutex);

}
@@ -394,6 +453,11 @@ static int __init balloon_init(void) 
	balloon_stats.balloon_low   = 0;

	balloon_stats.balloon_high  = 0;



	balloon_stats.schedule_delay = 1;

	balloon_stats.max_schedule_delay = 32;

	balloon_stats.retry_count = 1;

	balloon_stats.max_retry_count = 16;



	register_balloon(&balloon_sysdev);



	/*
@@ -447,6 +511,11 @@ BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages)); 
BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));

BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));



static SYSDEV_ULONG_ATTR(schedule_delay, 0444, balloon_stats.schedule_delay);

static SYSDEV_ULONG_ATTR(max_schedule_delay, 0644, balloon_stats.max_schedule_delay);

static SYSDEV_ULONG_ATTR(retry_count, 0444, balloon_stats.retry_count);

static SYSDEV_ULONG_ATTR(max_retry_count, 0644, balloon_stats.max_retry_count);



static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr,

			      char *buf)

{
@@ -508,6 +577,10 @@ static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR, 
static struct sysdev_attribute *balloon_attrs[] = {

	&attr_target_kb,

	&attr_target,

	&attr_schedule_delay.attr,

	&attr_max_schedule_delay.attr,

	&attr_retry_count.attr,

	&attr_max_retry_count.attr

};



static struct attribute *balloon_info_attrs[] = {