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cce3510313
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/20250611023439.2845785-1-lizhijian@fujitsu.com
Link: https://lkml.kernel.org/r/20250610062751.2365436-1-lizhijian@fujitsu.com
Fixes: 3718c02dbd ("acpi, hmat: calculate abstract distance with HMAT")
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Reviewed-by: Huang Ying <ying.huang@linux.alibaba.com>
Acked-by: Balbir Singh <balbirs@nvidia.com>
Reviewed-by: Donet Tom <donettom@linux.ibm.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.