xen: fix booting ballooned down hvm guest

Commit 96edd61dcf44362d3ef0bed1a5361e0ac7886a63 ("xen/balloon: don't
online new memory initially") introduced a regression when booting a
HVM domain with memory less than mem-max: instead of ballooning down
immediately the system would try to use the memory up to mem-max
resulting in Xen crashing the domain.

For HVM domains the current size will be reflected in Xenstore node
memory/static-max instead of memory/target.

Additionally we have to trigger the ballooning process at once.

Cc: <stable@vger.kernel.org> # 4.13
Fixes: 96edd61dcf44362d3ef0bed1a5361e0ac7886a63 ("xen/balloon: don't
       online new memory initially")

Reported-by: Simon Gaiser <hw42@ipsumj.de>
Suggested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

1 files changed, 13 insertions, 6 deletions

diff --git a/drivers/xen/xen-balloon.c b/drivers/xen/xen-balloon.c
index e89136ab851e..b437fccd4e62 100644
--- a/drivers/xen/xen-balloon.c
+++ b/drivers/xen/xen-balloon.c
@@ -57,7 +57,7 @@ static int register_balloon(struct device *dev);
 static void watch_target(struct xenbus_watch *watch,
                          const char *path, const char *token)
 {
-        unsigned long long new_target;
+        unsigned long long new_target, static_max;
         int err;
         static bool watch_fired;
         static long target_diff;
@@ -72,13 +72,20 @@ static void watch_target(struct xenbus_watch *watch,
          * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10.
          */
         new_target >>= PAGE_SHIFT - 10;
-        if (watch_fired) {
-                balloon_set_new_target(new_target - target_diff);
-                return;
+
+        if (!watch_fired) {
+                watch_fired = true;
+                err = xenbus_scanf(XBT_NIL, "memory", "static-max", "%llu",
+                                   &static_max);
+                if (err != 1)
+                        static_max = new_target;
+                else
+                        static_max >>= PAGE_SHIFT - 10;
+                target_diff = xen_pv_domain() ? 0
+                                : static_max - balloon_stats.target_pages;
         }
 
-        watch_fired = true;
-        target_diff = new_target - balloon_stats.target_pages;
+        balloon_set_new_target(new_target - target_diff);
 }
 static struct xenbus_watch target_watch = {
         .node = "memory/target",