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 X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 65B5DC433E0 for ; Tue, 11 Aug 2020 12:07:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4451B20782 for ; Tue, 11 Aug 2020 12:07:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728911AbgHKMHd (ORCPT ); Tue, 11 Aug 2020 08:07:33 -0400 Received: from elvis.franken.de ([193.175.24.41]:43751 "EHLO elvis.franken.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728790AbgHKMH1 (ORCPT ); Tue, 11 Aug 2020 08:07:27 -0400 Received: from uucp (helo=alpha) by elvis.franken.de with local-bsmtp (Exim 3.36 #1) id 1k5T3h-0002Ps-00; Tue, 11 Aug 2020 14:07:13 +0200 Received: by alpha.franken.de (Postfix, from userid 1000) id A82B6C0CC7; Tue, 11 Aug 2020 14:06:45 +0200 (CEST) Date: Tue, 11 Aug 2020 14:06:45 +0200 From: Thomas Bogendoerfer To: Huacai Chen Cc: Jiaxun Yang , "open list:MIPS" , Fuxin Zhang , Zhangjin Wu Subject: Re: [PATCH V3 1/2] MIPS: Loongson-3: Enable COP2 usage in kernel Message-ID: <20200811120645.GA6199@alpha.franken.de> References: <20200805121021.GA12598@alpha.franken.de> <1c3cb503-720f-059e-2bac-ae692203c389@flygoat.com> <20200807131357.GA11979@alpha.franken.de> <410cf75c-4cf5-94d8-fbc9-821d38f8a299@flygoat.com> <96dbe0be-7af6-b182-bbe0-534883539812@flygoat.com> <20200810141219.GA2844@alpha.franken.de> <106e65f5-d456-deaa-b47b-45b2a461b048@flygoat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Tue, Aug 11, 2020 at 02:45:05PM +0800, Huacai Chen wrote: > Hi, Thomas and Jiaxun, > > On Tue, Aug 11, 2020 at 10:18 AM Jiaxun Yang wrote: > > > > > > > > 在 2020/8/10 22:12, Thomas Bogendoerfer 写道: > > > On Sun, Aug 09, 2020 at 10:53:13PM +0800, Jiaxun Yang wrote: > > >> Thus we still need to enable CU2 with exception for user space, and we can > > >> always enable CU2 in > > >> kernel since kernel won't be compiled with hard-float. :-) > > > I see, how about the patch below > > That looks fine for me. > > Is it good with you, Huacai? > > There are two problems: > 1, zboot (arch/mips/boot/compressed/head.S) should be considered, > because the initial value of Status may or may not contain CU2. this comes with it's own memcpy/memset and stuff, I don't see a reason why COP2 needs to be enabled there, > 2, r4k_switch.S should set CU2 for the new process, otherwise it > cannot use gslq/gssq while it in kernel (Because the new process > doesn't contain CU2 in THERAD_STATUS. which is correct for all user space process, otherwise the whole cop2 exception thing wouldn't work. And if cop2 exception handling has been run it's set in THREAD_STATUS. > Though a process sets CU2 when it enters kernel, but it > only sets CU2 in hardware, not in THREAD_STATUS). A kernel thread will get THREAD_STATUS from current running kernel code, at least that's how I read this code: if (unlikely(p->flags & PF_KTHREAD)) { /* kernel thread */ unsigned long status = p->thread.cp0_status; memset(childregs, 0, sizeof(struct pt_regs)); ti->addr_limit = KERNEL_DS; p->thread.reg16 = usp; /* fn */ p->thread.reg17 = kthread_arg; p->thread.reg29 = childksp; p->thread.reg31 = (unsigned long) ret_from_kernel_thread; #if defined(CONFIG_CPU_R3000) || defined(CONFIG_CPU_TX39XX) status = (status & ~(ST0_KUP | ST0_IEP | ST0_IEC)) | ((status & (ST0_KUC | ST0_IEC)) << 2); #else status |= ST0_EXL; #endif childregs->cp0_status = status; return 0; } If there is still something missing, I want to find the root cause and not paper over it in r4k_switch.S and IMHO break COP2 handling for loongsoon completely. Thomas. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]