The kernel test has reported:

  BUG: unable to handle page fault for address: fffba000
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  *pde = 03171067 *pte = 00000000
  Oops: Oops: 0002 [#1]
  CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Tainted: G                T   6.18.0-rc2-00031-gec7f31b2a2d3 #1 NONE  a1d066dfe789f54bc7645c7989957d2bdee593ca
  Tainted: [T]=RANDSTRUCT
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
  EIP: memset (arch/x86/include/asm/string_32.h:168 arch/x86/lib/memcpy_32.c:17)
  Code: a5 8b 4d f4 83 e1 03 74 02 f3 a4 83 c4 04 5e 5f 5d 2e e9 73 41 01 00 90 90 90 3e 8d 74 26 00 55 89 e5 57 56 89 c6 89 d0 89 f7 <f3> aa 89 f0 5e 5f 5d 2e e9 53 41 01 00 cc cc cc 55 89 e5 53 57 56
  EAX: 0000006b EBX: 00000015 ECX: 001fefff EDX: 0000006b
  ESI: fffb9000 EDI: fffba000 EBP: c611fbf0 ESP: c611fbe8
  DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068 EFLAGS: 00010287
  CR0: 80050033 CR2: fffba000 CR3: 0316e000 CR4: 00040690
  Call Trace:
   poison_element (mm/mempool.c:83 mm/mempool.c:102)
   mempool_init_node (mm/mempool.c:142 mm/mempool.c:226)
   mempool_init_noprof (mm/mempool.c:250 (discriminator 1))
   ? mempool_alloc_pages (mm/mempool.c:640)
   bio_integrity_initfn (block/bio-integrity.c:483 (discriminator 8))
   ? mempool_alloc_pages (mm/mempool.c:640)
   do_one_initcall (init/main.c:1283)

Christoph found out this is due to the poisoning code not dealing
properly with CONFIG_HIGHMEM because only the first page is mapped but
then the whole potentially high-order page is accessed.

This went unnoticed for years probably because nobody has yet used a
mempool for order>0 pages before the new block code in -next.

We could give up on HIGHMEM here, but it's straightforward to fix this
with a loop that's mapping, poisoning or checking and unmapping
individual pages.

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202511111411.9ebfa1ba-lkp@intel.com
Analyzed-by: Christoph Hellwig <hch@lst.de>
Fixes: bdfedb76f4f5 ("mm, mempool: poison elements backed by slab allocator")
Tested-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
Will push to slab/for-next-fixes 
---
 mm/mempool.c | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/mm/mempool.c b/mm/mempool.c
index 1c38e873e546..d7bbf1189db9 100644
--- a/mm/mempool.c
+++ b/mm/mempool.c
@@ -68,10 +68,20 @@ static void check_element(mempool_t *pool, void *element)
 	} else if (pool->free == mempool_free_pages) {
 		/* Mempools backed by page allocator */
 		int order = (int)(long)pool->pool_data;
-		void *addr = kmap_local_page((struct page *)element);
 
-		__check_element(pool, addr, 1UL << (PAGE_SHIFT + order));
-		kunmap_local(addr);
+#ifdef CONFIG_HIGHMEM
+		for (int i = 0; i < (1 << order); i++) {
+			struct page *page = (struct page *)element;
+			void *addr = kmap_local_page(page + i);
+
+			__check_element(pool, addr, PAGE_SIZE);
+			kunmap_local(addr);
+		}
+#else
+		void *addr = page_address((struct page *)element);
+
+		__check_element(pool, addr, PAGE_SIZE << order);
+#endif
 	}
 }
 
@@ -97,10 +107,20 @@ static void poison_element(mempool_t *pool, void *element)
 	} else if (pool->alloc == mempool_alloc_pages) {
 		/* Mempools backed by page allocator */
 		int order = (int)(long)pool->pool_data;
-		void *addr = kmap_local_page((struct page *)element);
 
-		__poison_element(addr, 1UL << (PAGE_SHIFT + order));
-		kunmap_local(addr);
+#ifdef CONFIG_HIGHMEM
+		for (int i = 0; i < (1 << order); i++) {
+			struct page *page = (struct page *)element;
+			void *addr = kmap_local_page(page + i);
+
+			__poison_element(addr, PAGE_SIZE);
+			kunmap_local(addr);
+		}
+#else
+		void *addr = page_address((struct page *)element);
+
+		__poison_element(addr, PAGE_SIZE << order);
+#endif
 	}
 }
 #else /* CONFIG_SLUB_DEBUG_ON */

---
base-commit: e9a6fb0bcdd7609be6969112f3fbfcce3b1d4a7c
change-id: 20251113-mempool-poison-c081a82b9d54

Best regards,
-- 
Vlastimil Babka <vbabka@suse.cz>