[PATCH v2] mm/memblock: skip kmemleak for kasan_init()

[Qian Cai]

Kmemleak does not play well with KASAN (tested on both HPE Apollo 70 and
Huawei TaiShan 2280 aarch64 servers).

After calling start_kernel()->setup_arch()->kasan_init(), kmemleak early
log buffer went from something like 280 to 260000 which caused kmemleak
disabled and crash dump memory reservation failed. The multitude of
kmemleak_alloc() calls is from nested loops while KASAN is setting up
full memory mappings, so let early kmemleak allocations skip those
memblock_alloc_internal() calls came from kasan_init() given that those
early KASAN memory mappings should not reference to other memory.
Hence, no kmemleak false positives.

kasan_init
  kasan_map_populate [1]
    kasan_pgd_populate [2]
      kasan_pud_populate [3]
        kasan_pmd_populate [4]
          kasan_pte_populate [5]
            kasan_alloc_zeroed_page
              memblock_alloc_try_nid
                memblock_alloc_internal
                  kmemleak_alloc

[1] for_each_memblock(memory, reg)
[2] while (pgdp++, addr = next, addr != end)
[3] while (pudp++, addr = next, addr != end && pud_none(READ_ONCE(*pudp)))
[4] while (pmdp++, addr = next, addr != end && pmd_none(READ_ONCE(*pmdp)))
[5] while (ptep++, addr = next, addr != end && pte_none(READ_ONCE(*ptep)))

Signed-off-by: Qian Cai <cai@xxxxxx>
---

Changes since v1:
* only skip memblock_alloc_internal() calls came from kasan_int().

 arch/arm64/mm/kasan_init.c |  2 +-
 include/linux/memblock.h   |  1 +
 mm/memblock.c              | 19 +++++++++++--------
 3 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 63527e5..fcb2ca3 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -39,7 +39,7 @@ static phys_addr_t __init kasan_alloc_zeroed_page(int node)
 {
 	void *p = memblock_alloc_try_nid(PAGE_SIZE, PAGE_SIZE,
 					      __pa(MAX_DMA_ADDRESS),
-					      MEMBLOCK_ALLOC_ACCESSIBLE, node);
+					      MEMBLOCK_ALLOC_KASAN, node);
 	return __pa(p);
 }
 
diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index aee299a..3ef3086 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -320,6 +320,7 @@ static inline int memblock_get_region_node(const struct memblock_region *r)
 /* Flags for memblock allocation APIs */
 #define MEMBLOCK_ALLOC_ANYWHERE	(~(phys_addr_t)0)
 #define MEMBLOCK_ALLOC_ACCESSIBLE	0
+#define MEMBLOCK_ALLOC_KASAN		1
 
 /* We are using top down, so it is safe to use 0 here */
 #define MEMBLOCK_LOW_LIMIT 0
diff --git a/mm/memblock.c b/mm/memblock.c
index 9a2d5ae..abb9f7f 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -262,7 +262,8 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t size,
 	phys_addr_t kernel_end, ret;
 
 	/* pump up @end */
-	if (end == MEMBLOCK_ALLOC_ACCESSIBLE)
+	if (end == MEMBLOCK_ALLOC_ACCESSIBLE ||
+	    end == MEMBLOCK_ALLOC_KASAN)
 		end = memblock.current_limit;
 
 	/* avoid allocating the first page */
@@ -1412,13 +1413,15 @@ static void * __init memblock_alloc_internal(
 done:
 	ptr = phys_to_virt(alloc);
 
-	/*
-	 * The min_count is set to 0 so that bootmem allocated blocks
-	 * are never reported as leaks. This is because many of these blocks
-	 * are only referred via the physical address which is not
-	 * looked up by kmemleak.
-	 */
-	kmemleak_alloc(ptr, size, 0, 0);
+	/* Skip kmemleak for kasan_init() due to high volume. */
+	if (max_addr != MEMBLOCK_ALLOC_KASAN)
+		/*
+		 * The min_count is set to 0 so that bootmem allocated
+		 * blocks are never reported as leaks. This is because many
+		 * of these blocks are only referred via the physical
+		 * address which is not looked up by kmemleak.
+		 */
+		kmemleak_alloc(ptr, size, 0, 0);
 
 	return ptr;
 }
-- 
1.8.3.1