diff mbox series

[v4,2/6] xen: do not merge reserved pages in free_heap_pages()

Message ID 20220510022733.2422581-3-Penny.Zheng@arm.com (mailing list archive)
State New, archived
Headers show
Series populate/unpopulate memory when domain on static | expand

Commit Message

Penny Zheng May 10, 2022, 2:27 a.m. UTC 
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 accidently 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_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>
Suggested-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
v4 changes:
- commit message refinement
---
v3 changes:
- no changes
---
v2 changes:
- new commit
---
 xen/common/page_alloc.c | 2 ++
 1 file changed, 2 insertions(+)

Comments

Julien Grall May 16, 2022, 5:36 p.m. UTC | #1 
Hi Penny,

On 10/05/2022 03:27, Penny Zheng wrote:
> 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 accidently 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_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>
> Suggested-by: Julien Grall <jgrall@amazon.com>

NIT: In general, the tags are historically ordered. I.e I first sugested 
and then you wrote the patch. So the two tags should be inverted.

This can be done on commit:

Reviewed-by: Julien Grall <jgrall@amazon.com>

Cheers,
diff mbox series

Patch

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 5e569a48a2..290526adaf 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_reserved) ||
                  (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_reserved) ||
                  (PFN_ORDER(successor) != order) ||
                  (phys_to_nid(page_to_maddr(successor)) != node) )
                 break;