Commit bba072d1 authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Greg Kroah-Hartman
Browse files

hv_balloon: fix bugs in num_pages_onlined accounting 



Our num_pages_onlined accounting is buggy:
1) In case we're offlining a memory block which was present at boot (e.g.
   when there was no hotplug at all) we subtract 32k from 0 and as
   num_pages_onlined is unsigned get a very big positive number.

2) Commit 6df8d9aa ("Drivers: hv: balloon: Correctly update onlined
   page count") made num_pages_onlined counter accurate on onlining but
   totally incorrect on offlining for partly populated regions: no matter
   how many pages were onlined and what was actually added to
   num_pages_onlined counter we always subtract the full region (32k) so
   again, num_pages_onlined can wrap around zero. By onlining/offlining
   the same partly populated region multiple times we can make the
   situation worse.

Solve these issues by doing accurate accounting on offlining: walk HAS
list, check for covered range and gaps.

Fixes: 6df8d9aa ("Drivers: hv: balloon: Correctly update onlined page count")
Signed-off-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: default avatarK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 4f098af5

drivers/hv/hv_balloon.c

+69 −13
Original line number Diff line number Diff line
@@ -576,11 +576,65 @@ static struct hv_dynmem_device dm_device; 
static void post_status(struct hv_dynmem_device *dm);



#ifdef CONFIG_MEMORY_HOTPLUG

static inline bool has_pfn_is_backed(struct hv_hotadd_state *has,

				     unsigned long pfn)

{

	struct hv_hotadd_gap *gap;



	/* The page is not backed. */

	if ((pfn < has->covered_start_pfn) || (pfn >= has->covered_end_pfn))

		return false;



	/* Check for gaps. */

	list_for_each_entry(gap, &has->gap_list, list) {

		if ((pfn >= gap->start_pfn) && (pfn < gap->end_pfn))

			return false;

	}



	return true;

}



static unsigned long hv_page_offline_check(unsigned long start_pfn,

					   unsigned long nr_pages)

{

	unsigned long pfn = start_pfn, count = 0;

	struct hv_hotadd_state *has;

	bool found;



	while (pfn < start_pfn + nr_pages) {

		/*

		 * Search for HAS which covers the pfn and when we find one

		 * count how many consequitive PFNs are covered.

		 */

		found = false;

		list_for_each_entry(has, &dm_device.ha_region_list, list) {

			while ((pfn >= has->start_pfn) &&

			       (pfn < has->end_pfn) &&

			       (pfn < start_pfn + nr_pages)) {

				found = true;

				if (has_pfn_is_backed(has, pfn))

					count++;

				pfn++;

			}

		}



		/*

		 * This PFN is not in any HAS (e.g. we're offlining a region

		 * which was present at boot), no need to account for it. Go

		 * to the next one.

		 */

		if (!found)

			pfn++;

	}



	return count;

}



static int hv_memory_notifier(struct notifier_block *nb, unsigned long val,

			      void *v)

{

	struct memory_notify *mem = (struct memory_notify *)v;

	unsigned long flags;

	unsigned long flags, pfn_count;



	switch (val) {

	case MEM_ONLINE:
@@ -593,7 +647,19 @@ static int hv_memory_notifier(struct notifier_block *nb, unsigned long val, 


	case MEM_OFFLINE:

		spin_lock_irqsave(&dm_device.ha_lock, flags);

		dm_device.num_pages_onlined -= mem->nr_pages;

		pfn_count = hv_page_offline_check(mem->start_pfn,

						  mem->nr_pages);

		if (pfn_count <= dm_device.num_pages_onlined) {

			dm_device.num_pages_onlined -= pfn_count;

		} else {

			/*

			 * We're offlining more pages than we managed to online.

			 * This is unexpected. In any case don't let

			 * num_pages_onlined wrap around zero.

			 */

			WARN_ON_ONCE(1);

			dm_device.num_pages_onlined = 0;

		}

		spin_unlock_irqrestore(&dm_device.ha_lock, flags);

		break;

	case MEM_GOING_ONLINE:
@@ -612,19 +678,9 @@ static struct notifier_block hv_memory_nb = { 
/* Check if the particular page is backed and can be onlined and online it. */

static void hv_page_online_one(struct hv_hotadd_state *has, struct page *pg)

{

	struct hv_hotadd_gap *gap;

	unsigned long pfn = page_to_pfn(pg);



	/* The page is not backed. */

	if ((pfn < has->covered_start_pfn) || (pfn >= has->covered_end_pfn))

	if (!has_pfn_is_backed(has, page_to_pfn(pg)))

		return;



	/* Check for gaps. */

	list_for_each_entry(gap, &has->gap_list, list) {

		if ((pfn >= gap->start_pfn) && (pfn < gap->end_pfn))

			return;

	}



	/* This frame is currently backed; online the page. */

	__online_page_set_limits(pg);

	__online_page_increment_counters(pg);

CRA Git | Maintained and supported by SUSTech CRA and CCSE