From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4BCBAC433F5 for ; Tue, 14 Dec 2021 13:15:49 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4JCzQW3Nq3z3002 for ; Wed, 15 Dec 2021 00:15:47 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; secure) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=casper.20170209 header.b=XK2cZMDZ; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=infradead.org (client-ip=2001:8b0:10b:1236::1; helo=casper.infradead.org; envelope-from=willy@infradead.org; receiver=) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; secure) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=casper.20170209 header.b=XK2cZMDZ; dkim-atps=neutral Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4JCzPk5TXcz2yPV for ; Wed, 15 Dec 2021 00:15:05 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=+SjuTfMdZX234WsFLTKgVuTlJHNKJQ6+73Q7tXhFwCc=; b=XK2cZMDZBs7uBis/aCOTIfy5Id Woqbhfb9Jy/KCZQKrZRNKBni0OPi2vhjbBCFXVTZZwdfNF56JsdsQ62OYcF94p2H7RI22o/MO9Gze 79MLQCmvpO5GoJH/Wc3U5bT1kFBO7szsOivwVrpgEe7O/dPOSpHXg5RQnCMxsxVg4sEL5yLxKaGaN o2+DlolygGwKfZqa8tJ/Igl2vUcTDqbbAeBp3a6cbU7DI3cqvUrdvjVUunJvazeyk7h1+n8aLITmy mHMZsUktXu9JXz8kjVqgNxu5akRJTqIaRWUcQM0R8KY9P3voRZitjZtMGV0nZpFi23pCL7fHt8sO7 e7KFAFsQ==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mx7do-00DjQw-6u; Tue, 14 Dec 2021 13:14:48 +0000 Date: Tue, 14 Dec 2021 13:14:48 +0000 From: Matthew Wilcox To: Tiezhu Yang Subject: Re: [PATCH v2 0/2] kdump: simplify code Message-ID: References: <1639193588-7027-1-git-send-email-yangtiezhu@loongson.cn> <0c5cb37139af4f3e85cc2c5115d7d006@AcuMS.aculab.com> <36440c0f-8b8a-c401-684f-6f54ce9c061e@loongson.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <36440c0f-8b8a-c401-684f-6f54ce9c061e@loongson.cn> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "linux-ia64@vger.kernel.org" , Baoquan He , "linux-sh@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "x86@kernel.org" , "kexec@lists.infradead.org" , "linux-mips@vger.kernel.org" , "linux-kernel@vger.kernel.org" , David Laight , Vivek Goyal , Xuefeng Li , "linux-fsdevel@vger.kernel.org" , Andrew Morton , Dave Young , "linux-riscv@lists.infradead.org" , "linux-arm-kernel@lists.infradead.org" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Dec 14, 2021 at 06:03:11PM +0800, Tiezhu Yang wrote: > On 12/13/2021 10:43 PM, Matthew Wilcox wrote: > > On Mon, Dec 13, 2021 at 08:30:33AM +0000, David Laight wrote: > > > From: Matthew Wilcox > > > > Sent: 12 December 2021 11:48 > > > > > > > > On Sat, Dec 11, 2021 at 05:53:46PM +0000, David Laight wrote: > > > > > From: Tiezhu Yang > > > > > > Sent: 11 December 2021 03:33 > > > > > > > > > > > > v2: > > > > > > -- add copy_to_user_or_kernel() in lib/usercopy.c > > > > > > -- define userbuf as bool type > > > > > > > > > > Instead of having a flag to indicate whether the buffer is user or kernel, > > > > > would it be better to have two separate buffer pointers. > > > > > One for a user space buffer, the other for a kernel space buffer. > > > > > Exactly one of the buffers should always be NULL. > > > > > > > > No. You should be using an iov_iter instead. See > > > > https://lore.kernel.org/all/Ya4bdB0UBJCZhUSo@casper.infradead.org/ > > > > for a start on this. > > > > > > iov_iter gets horribly expensive... > > > > Oh, right. Reading the kcore is a high-performance path, my mistake. > > > > Hi, > > Thank you for your discussions. > > The intention of this patchset is to simplify the related code with no > functional changes and no side effects. > > At this moment, if you are OK, I will send v3 used with inline function > copy_to_user_or_kernel() to keep it simple, maybe other more changes can > be done in the future if no any side effect. That would be pointless. I already sent a series to remove this, which you were cc'd on.