[PATCH 4.4 12/76] xen: let alloc_xenballooned_pages() fail if not enough memory free

Greg Kroah-Hartman
2020-01-22T09:30:34Z

From: Juergen Gross <jgross@suse.com>

commit a1078e821b605813b63bf6bca414a85f804d5c66 upstream.

Instead of trying to allocate pages with GFP_USER in
add_ballooned_pages() check the available free memory via
si_mem_available(). GFP_USER is far less limiting memory exhaustion
than the test via si_mem_available().

This will avoid dom0 running out of memory due to excessive foreign
page mappings especially on ARM and on x86 in PVH mode, as those don't
have a pre-ballooned area which can be used for foreign mappings.

As the normal ballooning suffers from the same problem don't balloon
down more than si_mem_available() pages in one iteration. At the same
time limit the default maximum number of retries.

This is part of XSA-300.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/xen/balloon.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -584,8 +584,15 @@ static void balloon_process(struct work_
state = reserve_additional_memory();
}

- if (credit < 0)
- state = decrease_reservation(-credit, GFP_BALLOON);
+ if (credit < 0) {
+ long n_pages;
+
+ n_pages = min(-credit, si_mem_available());
+ state = decrease_reservation(n_pages, GFP_BALLOON);
+ if (state == BP_DONE && n_pages != -credit &&
+ n_pages < totalreserve_pages)
+ state = BP_EAGAIN;
+ }

state = update_schedule(state);

@@ -624,6 +631,9 @@ static int add_ballooned_pages(int nr_pa
}
}

+ if (si_mem_available() < nr_pages)
+ return -ENOMEM;
+
st = decrease_reservation(nr_pages, GFP_USER);
if (st != BP_DONE)
return -ENOMEM;
@@ -747,7 +757,7 @@ static int __init balloon_init(void)
balloon_stats.schedule_delay = 1;
balloon_stats.max_schedule_delay = 32;
balloon_stats.retry_count = 1;
- balloon_stats.max_retry_count = RETRY_UNLIMITED;
+ balloon_stats.max_retry_count = 4;

#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
set_online_page_callback(&xen_online_page);