mm: introduce memmap_alloc() to unify memory map allocation

There are several places that allocate memory for the memory map:
alloc_node_mem_map() for FLATMEM, sparse_buffer_init() and
__populate_section_memmap() for SPARSEMEM.

The memory allocated in the FLATMEM case is zeroed and it is never
poisoned, regardless of CONFIG_PAGE_POISON setting.

The memory allocated in the SPARSEMEM cases is not zeroed and it is
implicitly poisoned inside memblock if CONFIG_PAGE_POISON is set.

Introduce memmap_alloc() wrapper for memblock allocators that will be used
for both FLATMEM and SPARSEMEM cases and will makei memory map zeroing and
poisoning consistent for different memory models.

Link: https://lkml.kernel.org/r/20210714123739.16493-4-rppt@kernel.org
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Cc: Michal Simek <monstr@monstr.eu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/sparse.c b/mm/sparse.c
index fd29b3a..120bc8e 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -436,8 +436,7 @@ struct page __init *__populate_section_memmap(unsigned long pfn,
 	if (map)
 		return map;
 
-	map = memblock_alloc_try_nid_raw(size, size, addr,
-					  MEMBLOCK_ALLOC_ACCESSIBLE, nid);
+	map = memmap_alloc(size, size, addr, nid, false);
 	if (!map)
 		panic("%s: Failed to allocate %lu bytes align=0x%lx nid=%d from=%pa\n",
 		      __func__, size, PAGE_SIZE, nid, &addr);
@@ -464,8 +463,7 @@ static void __init sparse_buffer_init(unsigned long size, int nid)
 	 * and we want it to be properly aligned to the section size - this is
 	 * especially the case for VMEMMAP which maps memmap to PMDs
 	 */
-	sparsemap_buf = memblock_alloc_exact_nid_raw(size, section_map_size(),
-					addr, MEMBLOCK_ALLOC_ACCESSIBLE, nid);
+	sparsemap_buf = memmap_alloc(size, section_map_size(), addr, nid, true);
 	sparsemap_buf_end = sparsemap_buf + size;
 }