xen: let alloc_xenballooned_pages() fail if not enough memory free (a1078e82) · Commits · 戴 / test

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>

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);

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