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 6df8d9aaf3af ("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: 6df8d9aaf3af ("Drivers: hv: balloon: Correctly update onlined page count")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 5b8e1ad..7514a32 100644 (file)
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -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);