mm/memory-tier: fix abstract distance calculation overflow

commit cce3510 upstream.

In mt_perf_to_adistance(), the calculation of abstract distance (adist)
involves multiplying several int values including
MEMTIER_ADISTANCE_DRAM.

*adist = MEMTIER_ADISTANCE_DRAM *
		(perf->read_latency + perf->write_latency) /
		(default_dram_perf.read_latency + default_dram_perf.write_latency) *
		(default_dram_perf.read_bandwidth + default_dram_perf.write_bandwidth) /
		(perf->read_bandwidth + perf->write_bandwidth);

Since these values can be large, the multiplication may exceed the
maximum value of an int (INT_MAX) and overflow (Our platform did),
leading to an incorrect adist.

User-visible impact:
The memory tiering subsystem will misinterpret slow memory (like CXL)
as faster than DRAM, causing inappropriate demotion of pages from
CXL (slow memory) to DRAM (fast memory).

For example, we will see the following demotion chains from the dmesg, where
Node0,1 are DRAM, and Node2,3 are CXL node:
 Demotion targets for Node 0: null
 Demotion targets for Node 1: null
 Demotion targets for Node 2: preferred: 0-1, fallback: 0-1
 Demotion targets for Node 3: preferred: 0-1, fallback: 0-1

Change MEMTIER_ADISTANCE_DRAM to be a long constant by writing it with
the 'L' suffix.  This prevents the overflow because the multiplication
will then be done in the long type which has a larger range.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 3718c02 ("acpi, hmat: calculate abstract distance with HMAT")
Signed-off-by: Li Zhijian <[email protected]>
Reviewed-by: Huang Ying <[email protected]>
Acked-by: Balbir Singh <[email protected]>
Reviewed-by: Donet Tom <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: zhijianli88

include/linux/memory-tiers.h

@@ -18,7 +18,7 @@
  * adistance value (slightly faster) than default DRAM adistance to be part of
  * the same memory tier.
  */
-#define MEMTIER_ADISTANCE_DRAM	((4 * MEMTIER_CHUNK_SIZE) + (MEMTIER_CHUNK_SIZE >> 1))
+#define MEMTIER_ADISTANCE_DRAM	((4L * MEMTIER_CHUNK_SIZE) + (MEMTIER_CHUNK_SIZE >> 1))
 
 struct memory_tier;
 struct memory_dev_type {