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Wed, 14 Sep 2022 14:49:22 -0700 (PDT) Message-ID: Date: Wed, 14 Sep 2022 14:49:20 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.1.2 Subject: Re: [PATCH] mm/hugetlb: correct demote page offset logic Content-Language: en-US To: Andrew Morton Cc: Mike Kravetz , Muchun Song , Oscar Salvador , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20220914190917.3517663-1-opendmb@gmail.com> <20220914134927.16c229ccdc1a6b9da5d698c3@linux-foundation.org> From: Doug Berger In-Reply-To: <20220914134927.16c229ccdc1a6b9da5d698c3@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1663192164; a=rsa-sha256; cv=none; b=wZScCturyvGgwn+TAzNYLY91HFfrDV70QRfGIdTQxoKBMeya30suO4ohINnQx9E2nE8WKk L5cBqD9l0YIlRKcMSpUO2RtHNTjRfz3wgiPfsp+PAbb0h4Z8TrPqgdqhcGM3xNvrRwTAww 9Bh1H3j6FyxQbsAi0F1gW/hxOSK1lgo= ARC-Authentication-Results: i=1; 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dmarc=pass (policy=none) header.from=gmail.com X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: n5ahegib1fa1ctoap1cmmaezbz7n74wt X-Rspamd-Queue-Id: AB477A00A5 X-HE-Tag: 1663192164-169925 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: On 9/14/2022 1:49 PM, Andrew Morton wrote: > On Wed, 14 Sep 2022 12:09:17 -0700 Doug Berger wrote: > >> With gigantic pages it may not be true that struct page structures >> are contiguous across the entire gigantic page. The nth_page macro >> is used here in place of direct pointer arithmetic to correct for >> this. > > What were the user-visible runtime effects of this bug? As Mike said this would only conceptually be a problem for systems with CONFIG_SPARSEMEM && !CONFIG_SPARSEMEM_VMEMMAP, and could cause kernel address exceptions or memory corruption with unpredictable side effects. However, I am unaware of a system other than perhaps the PS3 that uses the classic sparse addressing, so the odds of such a system also using gigantic hugetlbfs pages that it wants to demote is likely quite small. Thanks, -Doug