[Xen-devel] [PATCH v2] xen: fix booting ballooned down hvm guest

[Juergen Gross <jgross@xxxxxxxx>]

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@xxxxxxxxxxxxxxx> # 4.13
Fixes: 96edd61dcf44362d3ef0bed1a5361e0ac7886a63 ("xen/balloon: don't
       online new memory initially")

Reported-by: Simon Gaiser <hw42@xxxxxxxxx>
Suggested-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 drivers/xen/xen-balloon.c | 19 +++++++++++++------
 1 file 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",
-- 
2.12.3


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