[PATCHv2 10/10] xen/balloon: pre-allocate p2m entries for ballooned pages

[David Vrabel <david.vrabel@citrix.com>]

Pages returned by alloc_xenballooned_pages() will be used for grant
mapping which will call set_phys_to_machine() (in PV guests).

Ballooned pages are set as INVALID_P2M_ENTRY in the p2m and thus may
be using the (shared) missing tables and a subsequent
set_phys_to_machine() will need to allocate new tables.

Since the grant mapping may be done from a context that cannot sleep,
the p2m entries must already be allocated.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
 drivers/xen/balloon.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index fd6970f3..8932d10 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -541,6 +541,7 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages)
 {
 	int pgno = 0;
 	struct page *page;
+	int ret = -ENOMEM;
 
 	mutex_lock(&balloon_mutex);
 
@@ -550,6 +551,11 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages)
 		page = balloon_retrieve(true);
 		if (page) {
 			pages[pgno++] = page;
+#ifdef CONFIG_XEN_HAVE_PVMMU
+			ret = xen_alloc_p2m_entry(page_to_pfn(page));
+			if (ret < 0)
+				goto out_undo;
+#endif
 		} else {
 			enum bp_state st;
 
@@ -576,7 +582,7 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages)
  out_undo:
 	mutex_unlock(&balloon_mutex);
 	free_xenballooned_pages(pgno, pages);
-	return -ENOMEM;
+	return ret;
 }
 EXPORT_SYMBOL(alloc_xenballooned_pages);
 
-- 
2.1.4