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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BD36AC4332F for ; Mon, 13 Dec 2021 14:44:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239731AbhLMOoC (ORCPT ); Mon, 13 Dec 2021 09:44:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44258 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234143AbhLMOoB (ORCPT ); Mon, 13 Dec 2021 09:44:01 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AD9BBC061574; Mon, 13 Dec 2021 06:44:01 -0800 (PST) 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=WN0UBRQSaVnqth1lPLeu1h3m2LsiDV8FPn8ylQJCtw8=; b=p3RXvBFb2so3jcvbNtFm9YqLoy Db6NHe524T07Hi4ZiyLaxSrQxikXMESk//fQ258u8C8HwL4tvSiBf9GqWsbjwUJj0MpZb99Q3r7Gn U8I4uIl0lJmqmxhPuXIO2nSstlKIwd5Iq6DRxuuB+XewafpJUhhMkxy8nn3Di3UE6QlKKR/tkzwqN 82AY01mLzM89zRBTPtsel1HfkWhp0iwheQwoshPsb7I7IaBR/GEnNFzI6tMIojo9QsGW9FNyl0q0u 8cNlSbM2lT2wank3wbXnRWxj4TWJs6JahqJ/E/e+nJSdtlRCOOK0S/1TpqDLQhR1BBCV9fSEeWv7a TVTjir2Q==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mwmYS-00Csn8-Vy; Mon, 13 Dec 2021 14:43:53 +0000 Date: Mon, 13 Dec 2021 14:43:52 +0000 From: Matthew Wilcox To: David Laight Cc: 'Tiezhu Yang' , Dave Young , Baoquan He , Vivek Goyal , Andrew Morton , "linux-arm-kernel@lists.infradead.org" , "linux-ia64@vger.kernel.org" , "linux-mips@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-riscv@lists.infradead.org" , "linux-sh@vger.kernel.org" , "x86@kernel.org" , "linux-fsdevel@vger.kernel.org" , "kexec@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Xuefeng Li 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.