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Thu, 05 Nov 2026 23:23:58 -0800 (PST) Received: from LAPTOP-AVI.lan ([2a06:c701:475e:f800:a7fc:23a0:3fe2:eb8b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-492d3d609c8sm2201123f8f.6.2026.11.05.23.23.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Nov 2026 23:23:57 -0800 (PST) From: Avi Weiss To: rppt@kernel.org Cc: akpm@linux-foundation.org, rientjes@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] mm/mm_init: avoid overflow in percentage-based core sizing Date: Fri, 6 Nov 2026 09:23:55 +0200 Message-ID: <20261106072354.2234189-2-thnkslprpt@gmail.com> X-Mailer: git-send-email 2.43.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The kernelcore= and movablecore= percentage calculations multiply the total number of pages before dividing. On 32-bit kernels, the intermediate unsigned long product can overflow, producing incorrect memory zone boundaries. With 2 GiB of RAM and kernelcore=100%, a 32-bit HIGHMEM kernel incorrectly creates ZONE_MOVABLE. Use mult_frac() to calculate both percentages without overflowing the intermediate product. Fixes: a5c6d6509342 ("mm, page_alloc: extend kernelcore and movablecore for percent") Signed-off-by: Avi Weiss --- mm/mm_init.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index 2a0e782a151d..27a50ecd5c20 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -7,6 +7,7 @@ * */ #include +#include #include #include #include @@ -448,11 +449,9 @@ static void __init find_zone_movable_pfns_for_nodes(void) * amount of necessary memory. */ if (required_kernelcore_percent) - required_kernelcore = (totalpages * 100 * required_kernelcore_percent) / - 10000UL; + required_kernelcore = mult_frac(totalpages, required_kernelcore_percent, 100); if (required_movablecore_percent) - required_movablecore = (totalpages * 100 * required_movablecore_percent) / - 10000UL; + required_movablecore = mult_frac(totalpages, required_movablecore_percent, 100); /* * If movablecore= was specified, calculate what size of base-commit: 36aad21d50d1af3f6954bb0c988257a908202477 -- 2.43.0