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<5efeb909-3e02-ba14-7a86-f18562a2fe69@i-love.sakura.ne.jp> <8590eb4c-256b-9ab0-5291-de8ec8d75276@nvidia.com> <40bd424d-6c4d-8b03-5d97-c572ca777b77@i-love.sakura.ne.jp> From: John Hubbard Message-ID: <1174ed3e-d33c-6de9-3873-b122013b295a@nvidia.com> Date: Sat, 7 Nov 2020 21:00:26 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <40bd424d-6c4d-8b03-5d97-c572ca777b77@i-love.sakura.ne.jp> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL101.nvidia.com (172.20.187.10) To HQMAIL107.nvidia.com (172.20.187.13) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1604811630; bh=0F6FyPkKxLlO1J2Iwb+PkNH/lUr59fnpYgGGqGjgy9s=; h=Subject:To:CC:References:From:Message-ID:Date:User-Agent: MIME-Version:In-Reply-To:Content-Type:Content-Language: Content-Transfer-Encoding:X-Originating-IP:X-ClientProxiedBy; b=guvtqofOgQi9R86WymuUok80xhTaRW7Ydwf2bzPE7ZlgTFvHZztcJn+uTj9QO4BLF FVi8q2YXZ1wk9KHvnu2QyDtNFM7RXARHcy2oJaUiMthsvwIWx6khreikAVIwciH4gp tNgaUfiAKzRTQn53dtPM/bNCqTkEWS2WLCNXvFRuBUEO0T/LLRMapBerGC/uuy5mFu leFuUbf8jTdR43PTybiEgbfUdd3AaqUPZK31V34Yf1y52DVl9cI6QiThcjGrG4yU10 +xNIvr2Wa2OiPvV57W8nJMWm2I3Qo87x+KbFYjhzNoGkT5nVW15OTpPPWLiHZ+pyBy aB7xU0mlXA4Dg== Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/7/20 8:12 PM, Tetsuo Handa wrote: > On 2020/11/08 11:17, John Hubbard wrote: >>> Excuse me, but Documentation/core-api/pin_user_pages.rst says >>> "CASE 5: Pinning in order to _write_ to the data within the page" >>> while tomoyo_dump_page() is for "_read_ the data within the page". >>> Do we want to convert to pin_user_pages_remote() or lock_page() ? >>> >> >> Sorry, I missed the direction here, was too focused on the Case 5 >> aspect. Yes. Case 5 (which, again, I think we're about to re-document) >> is only about *writing* to data within the page. >> >> So in this case, where it is just reading from the page, I think it's >> already from a gup vs pup point of view. >> >> btw, it's not clear to me whether the current code is susceptible to any >> sort of problem involving something writing to the page while it >> is being dumped (I am curious). But changing from gup to pup wouldn't >> fix that, if it were a problem. It a separate question from this patch. > > The "struct page" tomoyo_dump_page() accesses is argv/envp arguments passed > to execve() syscall. Therefore, these pages are not visible from threads > except current thread, and thus there is no possibility that these pages > are modified by other threads while current thread is reading. > Perfect. So since I accidentally left out the word "correct" above (I meant to write, "it's already correct"), let me be extra clear: Souptick, we should just drop this patch. thanks, -- John Hubbard NVIDIA