From: Juergen Gross jgross@suse.com
[ Upstream commit a1078e821b605813b63bf6bca414a85f804d5c66 ]
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: Sasha Levin sashal@kernel.org --- drivers/xen/balloon.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c index d37dd5bb7a8f..559768dc2567 100644 --- a/drivers/xen/balloon.c +++ b/drivers/xen/balloon.c @@ -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);