[xen staging] xen: do not merge reserved pages in free_heap_pages()

[patchbot@xxxxxxx]

commit 7d3f8a2a26f2fd9c4d830820b8ad68af4e91f409
Author:     Penny Zheng <Penny.Zheng@xxxxxxx>
AuthorDate: Tue Aug 16 10:36:52 2022 +0800
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Wed Aug 24 10:36:20 2022 +0100

    xen: do not merge reserved pages in free_heap_pages()
    
    The code in free_heap_pages() will try to merge pages with the
    successor/predecessor if pages are suitably aligned. So if the pages
    reserved are right next to the pages given to the heap allocator,
    free_heap_pages() will merge them, and give the reserved pages to heap
    allocator accidentally as a result.
    
    So in order to avoid the above scenario, this commit updates 
free_heap_pages()
    to check whether the predecessor and/or successor has PGC_static set,
    when trying to merge the about-to-be-freed chunk with the predecessor
    and/or successor.
    
    Suggested-by: Julien Grall <jgrall@xxxxxxxxxx>
    Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
---
 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 00fa24e330..bfd4150be7 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1483,6 +1483,7 @@ 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_static) ||
                  (PFN_ORDER(predecessor) != order) ||
                  (phys_to_nid(page_to_maddr(predecessor)) != node) )
                 break;
@@ -1506,6 +1507,7 @@ 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_static) ||
                  (PFN_ORDER(successor) != order) ||
                  (phys_to_nid(page_to_maddr(successor)) != node) )
                 break;
--
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