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

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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>
This commit is contained in:
Juergen Gross 2019-06-19 11:00:56 +02:00
parent b23e5844df
commit a1078e821b
1 changed files with 13 additions and 3 deletions
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16
drivers/xen/balloon.c
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@ -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);