Re: [PATCHv6 09/17] mm/sparse: Check memmap alignment for compound_info_has_mask()
From: David Hildenbrand (Arm)
Date: Thu Feb 05 2026 - 09:06:50 EST
On 2/5/26 14:31, David Hildenbrand (Arm) wrote:
On 2/2/26 16:56, Kiryl Shutsemau wrote:
If page->compound_info encodes a mask, it is expected that vmemmap to be
naturally aligned to the maximum folio size.
Add a VM_BUG_ON() to check the alignment.
Signed-off-by: Kiryl Shutsemau <kas@xxxxxxxxxx>
Acked-by: Zi Yan <ziy@xxxxxxxxxx>
---
mm/sparse.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/mm/sparse.c b/mm/sparse.c
index b5b2b6f7041b..6c9b62607f3f 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -600,6 +600,13 @@ void __init sparse_init(void)
BUILD_BUG_ON(!is_power_of_2(sizeof(struct mem_section)));
memblocks_present();
+ if (compound_info_has_mask()) {
+ unsigned long alignment;
+
+ alignment = MAX_FOLIO_NR_PAGES * sizeof(struct page);
+ VM_BUG_ON(!IS_ALIGNED((unsigned long) pfn_to_page(0), alignment));
No VM_BUG_ON. VM_WARN_ON_ONCE() should be good enough, no?
As discussed in the other thread, is checking for MAX_FOLIO_NR_PAGES alignment sufficient?
And after further discussions, we could use MAX_FOLIO_VMEMMAP_ALIGN macro once we have that.
--
Cheers,
David