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b=klbBWQRkmK9TYPKbbsNeq0EH2IngBOVJqXiy0StmkIEyS4rXK6xUuJLUrPJxut1u4 OsgI+fYNfw8ZFtnirRPdmFLIWTA3Misacd8xG8DH3/YXbBIpSqfcNn999pI8MLySXX KfoSiRocJUi6yPSHPjhwN6fJ9HCLriBqp0zEOuoY= Date: Tue, 10 Jun 2025 14:02:28 -0700 From: Andrew Morton To: Li Zhijian Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ying Huang , Balbir Singh , Donet Tom , Oscar Salvador Subject: Re: [PATCH] mm/memory-tier: Fix abstract distance calculation overflow Message-Id: <20250610140228.7836d333cea973a8171686fb@linux-foundation.org> In-Reply-To: <20250610062751.2365436-1-lizhijian@fujitsu.com> References: <20250610062751.2365436-1-lizhijian@fujitsu.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 813E6180013 X-Rspamd-Server: rspam03 X-Rspam-User: X-Stat-Signature: gst14xa5ewwkpnjbnscss3g9h4sxb4rm X-HE-Tag: 1749589350-220450 X-HE-Meta: U2FsdGVkX18ls8xkQBX3zpCTcAbeLlEissvv0wLZ8FfqZuAJT/v/Rze0saX0/tTjdtcy2bYZ1eN+lPxcCANMYlubfGXFXvvvCHcljfILgoiF8XCcxdz3x+Pn6qVWZu++5kKlChHi2yKALpKL0VsVDcI451SykOeGe12Wcky4O6tBYTIsIXhD/WS4s6CMHwgmAOki/DxBBwB61nuiguoipGPuiJ8JYt3/7J7b1wojsFHrFb+Q/ZP9m287miKEoED4O1C5DVBek0XWhiMfpR6zraua7avpu/yxvrFGXtRMDtNlB0QUa0qDaEdnI1dZFxIm3WFptp+cEM7luOhOY/1C3fCKgL1ySQgUjGfcDD7HXZ3gCo0tpfKNxvRZe12S1QrcQvk690NKQq+fKrUQjrRKR1hvrl/T7v/w92kDQUhtpbZGzYi3mg+lPS6PFQvyL7mProIoJ9ojqsb4etba7fv1by5pmpW9LoxBVai4i8lMS6EUCIktvsR0VsT3De8G4vXsbzej8rNPmCZjuwngR6rciQc4TbCuIhkgLUQpU7cY23dU6wk4iDELT2ZpI+tnFCTni1ZJWK1T3O9No+QVRZ5eX8A9/vdAwT6RS3LJ5srfLu1K1VnRxOOzonikvMD8MpMIGnU2L3FIP1bvM47o4m9YEAd/mHqc5wxGLo9BqTiELYlD9gVllZdvx0tcxpkC2nH+rTOudxWHjo9pWBO8LpT75nZM9UND52vSabWvCeG3KANB/MKL+dk+k0IXZ2/3PlAQkMHGg6jnLihb+yfzLiDz8A+T71QlD8jpWY0ldlSxBtV0Aw7Xrvy4QuWwaNTmxwfQXEGM89Nhq3oDan8EtrruzTjx1wP9/ezJjBcYwWy1vHoKSMKH/bTZ06H/tHbSHf9xQ0LHKOl9DOGENn9TuPFcqsj0VrXTArRHpchkNUq4d5HyQ1a6+8kzcZhYuzO4qz8+nerf+9bCtZAg0A2qRta ICCih7Lj zjjWbWgpIVArOuRjggUL/gA+q9eZeh/tAyHlRsiZ1gkoMovQ3Aqjv1OTQqgIbtqnfvVJS1Hix8R6vwg0SimtCEUTBg40aENK8s/Uxg1IJTXVNzBlcUGATOk6g/z+fwgDl/mfhGrzr+xWahn3BNj8RdYbf+5TGriY0Oc+CiZr6i/AuZ3NwwSbms5x5QzhRCiPYVYK2uEZ7jLVkZ1iNrSWkej7/lwQDlDHL8T/kPmI06MGoD2hCd1GKIXFrOVMRbJ7qU5HDBSsZS6Dl/5ROBHQd7zZulBMNThCUgGdGz9DVSXGsFQTWqSJ+dvHGjtXasIRIh9rCqHbdHmyTCbJTyM0WuiE8aQ== 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: On Tue, 10 Jun 2025 14:27:51 +0800 Li Zhijian wrote: > 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. Thanks. The changelog doesn't describe the userspace-visible effects of this. Please always include this info. I'll assume "minor" and it's been this way for a while so I'll add a cc:stable to this change and shall queue it for 6.17-rc1, so it will be backported into 6.17.x and earlier kernels at a later time.