xen/balloon: Avoid OOM when requesting highmem

If highmem pages are requested from the balloon on a system without
highmem, the implementation of alloc_xenballooned_pages will allocate
all available memory trying to find highmem pages to return. Allow
low memory to be returned when highmem pages are requested to avoid
this loop.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index a767884..31ab82f 100644 (file)
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -501,7 +501,7 @@ EXPORT_SYMBOL_GPL(balloon_set_new_target);
  * alloc_xenballooned_pages - get pages that have been ballooned out
  * @nr_pages: Number of pages to get
  * @pages: pages returned
- * @highmem: highmem or lowmem pages
+ * @highmem: allow highmem pages
  * @return 0 on success, error otherwise
  */
 int alloc_xenballooned_pages(int nr_pages, struct page **pages, bool highmem)
@@ -511,7 +511,7 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages, bool highmem)
        mutex_lock(&balloon_mutex);
        while (pgno < nr_pages) {
                page = balloon_retrieve(highmem);
-               if (page && PageHighMem(page) == highmem) {
+               if (page && (highmem || !PageHighMem(page))) {
                        pages[pgno++] = page;
                } else {
                        enum bp_state st;