Patch "xen: fix booting ballooned down hvm guest" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

xen: fix booting ballooned down hvm guest

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xen-fix-booting-ballooned-down-hvm-guest.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Juergen Gross <[email protected]>
Date: Thu, 26 Oct 2017 11:50:56 +0200
Subject: xen: fix booting ballooned down hvm guest

From: Juergen Gross <[email protected]>

commit 5266b8e4445cc836c46689d80a9ff539fa3bfbda upstream.

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.

---
 drivers/xen/xen-balloon.c |   19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

@@ -57,7 +57,7 @@ static int register_balloon(struct devic
 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_w
 	 * 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",

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/xen-gntdev-avoid-out-of-bounds-access-in-case-of-partial-gntdev_mmap.patch queue-4.13/xen-fix-booting-ballooned-down-hvm-guest.patch