From 4a69c909deb0dd3cae653d14ac0ff52d5440a19c Mon Sep 17 00:00:00 2001
From: David Vrabel <david.vrabel@citrix.com>
Date: Wed, 22 Jul 2015 14:50:37 +0100
Subject: [PATCH] xen/balloon: pre-allocate p2m entries for ballooned pages

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>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 drivers/xen/balloon.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 25fd1bd949d8..f56662324a47 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -602,6 +602,11 @@ 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 {
 			ret = add_ballooned_pages(nr_pages - pgno);
 			if (ret < 0)
-- 
GitLab