Add "xen/balloon: add late_initcall_sync() for initial ballooning" patch

Another fix for thread-based balloon driver

Fixes QubesOS/qubes-issues#7023

(cherry picked from commit c7f2b45)

0001-xen-balloon-add-late_initcall_sync-for-initial-ballo.patch

@@ -0,0 +1,57 @@
+From 30dc0817d3982c77b4eb4d03889eabb49e182371 Mon Sep 17 00:00:00 2001
+From: Juergen Gross <[email protected]>
+Date: Thu, 28 Oct 2021 12:59:52 +0200
+Subject: [PATCH] xen/balloon: add late_initcall_sync() for initial ballooning
+ done
+
+When running as PVH or HVM guest with actual memory < max memory the
+hypervisor is using "populate on demand" in order to allow the guest
+to balloon down from its maximum memory size. For this to work
+correctly the guest must not touch more memory pages than its target
+memory size as otherwise the PoD cache will be exhausted and the guest
+is crashed as a result of that.
+
+In extreme cases ballooning down might not be finished today before
+the init process is started, which can consume lots of memory.
+
+In order to avoid random boot crashes in such cases, add a late init
+call to wait for ballooning down having finished for PVH/HVM guests.
+
+Cc: <[email protected]>
+Reported-by: Marek Marczykowski-Górecki <[email protected]>
+Signed-off-by: Juergen Gross <[email protected]>
+---
+ drivers/xen/balloon.c | 20 ++++++++++++++++++++
+ 1 file changed, 20 insertions(+)
+
+diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
+index 1911a62a6d9c..60314e69f7fa 100644
+--- a/drivers/xen/balloon.c
++++ b/drivers/xen/balloon.c
+@@ -765,3 +765,23 @@ static int __init balloon_init(void)
+ 	return 0;
+ }
+ subsys_initcall(balloon_init);
++
++static int __init balloon_wait_finish(void)
++{
++	if (!xen_domain())
++		return -ENODEV;
++
++	/* PV guests don't need to wait. */
++	if (xen_pv_domain() || !current_credit())
++		return 0;
++
++	pr_info("Waiting for initial ballooning down having finished.\n");
++
++	while (current_credit())
++		schedule_timeout_interruptible(HZ / 10);
++
++	pr_info("Initial ballooning down finished.\n");
++
++	return 0;
++}
++late_initcall_sync(balloon_wait_finish);
+-- 
+2.31.1
+

kernel.spec.in

@@ -130,6 +130,7 @@ Patch11: 0012-xen-blkfront-prepare-request-locally-only-then-put-i.patch
 Patch12: 0013-xen-pcifront-pciback-Update-pciif.h-with-err-and-res.patch
 Patch13: 0014-xen-pciback-add-attribute-to-allow-MSI-enable-flag-w.patch
 Patch14: 0001-Revert-xen-netback-Check-for-hotplug-status-existenc.patch
+Patch16: 0001-xen-balloon-add-late_initcall_sync-for-initial-ballo.patch
 
 %description
 Qubes Dom0 kernel.