[PATCH v2 2/6] xen/arm: do not merge reserved pages in free_heap_pages()

[Penny Zheng <Penny.Zheng@arm.com>]

There is a slim chance that free_heap_pages() may decide to merge a chunk
from the static region(PGC_reserved) with the about-to-be-free chunk.

So in order to avoid the above scenario, this commit updates free_heap_pages()
to check whether the predecessor and/or successor has PGC_reserved set,
when trying to merge the about-to-be-freed chunk with the predecessor
and/or successor.

Signed-off-by: Penny Zheng <penny.zheng@arm.com>
---
v2 changes:
- new commit
---
 xen/common/page_alloc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 9a3e9c1328..8ba38bca9a 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1479,6 +1479,7 @@ static void free_heap_pages(
             /* Merge with predecessor block? */
             if ( !mfn_valid(page_to_mfn(predecessor)) ||
                  !page_state_is(predecessor, free) ||
+                 (predecessor->count_info & PGC_reserved) ||
                  (PFN_ORDER(predecessor) != order) ||
                  (phys_to_nid(page_to_maddr(predecessor)) != node) )
                 break;
@@ -1502,6 +1503,7 @@ static void free_heap_pages(
             /* Merge with successor block? */
             if ( !mfn_valid(page_to_mfn(successor)) ||
                  !page_state_is(successor, free) ||
+                 (successor->count_info & PGC_reserved) ||
                  (PFN_ORDER(successor) != order) ||
                  (phys_to_nid(page_to_maddr(successor)) != node) )
                 break;
-- 
2.25.1