kfence: skip all GFP_ZONEMASK allocations

Allocation requests outside ZONE_NORMAL (MOVABLE, HIGHMEM or DMA) cannot
be fulfilled by KFENCE, because KFENCE memory pool is located in a zone
different from the requested one.

Because callers of kmem_cache_alloc() may actually rely on the
allocation to reside in the requested zone (e.g.  memory allocations
done with __GFP_DMA must be DMAable), skip all allocations done with
GFP_ZONEMASK and/or respective SLAB flags (SLAB_CACHE_DMA and
SLAB_CACHE_DMA32).

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 0ce20dd ("mm: add Kernel Electric-Fence infrastructure")
Signed-off-by: Alexander Potapenko <[email protected]>
Reviewed-by: Marco Elver <[email protected]>
Acked-by: Souptick Joarder <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Souptick Joarder <[email protected]>
Cc: <[email protected]>	[5.12+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: ramosian-glider

mm/kfence/core.c

@@ -740,6 +740,15 @@ void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
 	if (size > PAGE_SIZE)
 		return NULL;
 
+	/*
+	 * Skip allocations from non-default zones, including DMA. We cannot
+	 * guarantee that pages in the KFENCE pool will have the requested
+	 * properties (e.g. reside in DMAable memory).
+	 */
+	if ((flags & GFP_ZONEMASK) ||
+	    (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32)))
+		return NULL;
+
 	/*
 	 * allocation_gate only needs to become non-zero, so it doesn't make
 	 * sense to continue writing to it and pay the associated contention