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Tue, 10 Jun 2025 14:33:12 +0800 From: "Huang, Ying" To: Li Zhijian Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Ying Huang Subject: Re: [PATCH] mm/memory-tier: Fix abstract distance calculation overflow In-Reply-To: <20250610062751.2365436-1-lizhijian@fujitsu.com> (Li Zhijian's message of "Tue, 10 Jun 2025 14:27:51 +0800") References: <20250610062751.2365436-1-lizhijian@fujitsu.com> Date: Tue, 10 Jun 2025 14:33:10 +0800 Message-ID: <877c1kcdi1.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Stat-Signature: c1trwjcnj9g1rn4rypti9u97yfyrbft1 X-Rspamd-Queue-Id: 5B1D014000D X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1749537197-686935 X-HE-Meta: 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 DXHC5Y90 NzOKICMcftmWEu9xKLkiN9q9AjjZYzxFJdMD7uSf7hyUeIdL0MLqqn/CbsFZA9q2A2S8hFsTjoGJw68eFU96sd7XsuqHKbUc0M8bF/xBVDxxhDkbPHzZpCyOYNW76FoR7A2CS1dPA3q/7UlF1VG34zayx6gTB15xySj8gLrH2Tfswg8DuSGMW0i4snvrOTg2XmJuVkF38yNp4Ec6DPGBFrwnbFQAfRsxQsgXa6L3RpT40QHLFqPqrmgVcFVbDsZJTHbEWsN46pZtSKc6mKnKk/RcrlawkNvkOnn+MMVIir8+83fnmwjiFLWlphGMdSXUKlpkP3ERmVkzfuepw+Ra2iiCuaNYw6emBq9DBoMHAmEJjAhRtBWO6SDgr7gm81abFC1hL X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Li Zhijian writes: > 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. > > 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. > > Fixes: 3718c02dbd4c ("acpi, hmat: calculate abstract distance with HMAT") > Cc: Ying Huang > Signed-off-by: Li Zhijian Good catch! Feel free to add Reviewed-by: Huang Ying in the future version. --- Best Regards, Huang, Ying [snip]