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Commit a1078e82 authored by Juergen Gross's avatar Juergen Gross
Browse files

xen: let alloc_xenballooned_pages() fail if not enough memory free 



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: default avatarJuergen Gross <jgross@suse.com>
parent b23e5844

drivers/xen/balloon.c

+13 −3
Original line number Diff line number Diff line
@@ -538,8 +538,15 @@ static void balloon_process(struct work_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);
@@ -578,6 +585,9 @@ static int add_ballooned_pages(int nr_pages) 
		}

	}



	if (si_mem_available() < nr_pages)

		return -ENOMEM;



	st = decrease_reservation(nr_pages, GFP_USER);

	if (st != BP_DONE)

		return -ENOMEM;
@@ -710,7 +720,7 @@ 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);