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=-7.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 88193C433E7 for ; Wed, 2 Sep 2020 06:54:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 692D82067C for ; Wed, 2 Sep 2020 06:54:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726140AbgIBGy3 (ORCPT ); Wed, 2 Sep 2020 02:54:29 -0400 Received: from mail-il1-f196.google.com ([209.85.166.196]:45851 "EHLO mail-il1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726419AbgIBGyX (ORCPT ); Wed, 2 Sep 2020 02:54:23 -0400 Received: by mail-il1-f196.google.com with SMTP id q6so4059490ild.12 for ; Tue, 01 Sep 2020 23:54:23 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=NXkrhht6q/ABGeb2TBNJsVr+vrAGAjQ8EtRde81433k=; b=Dwq74fY8RCugUnlhM8ctg9x75N4TKoB3nUQ9Ted3DuNY6PCHbVWqjYe/Y0ucnAaMO9 qzzUq9VL1iaU1C3gCpwQJ8i4oYr7CvWzrj1yPSoyQnSXNRrrvEzu2AuYk7XwH3R1pXwu xwoLNj5EYKDJ36hve9bky/8gpEZ03dk9T3gjVKhkG11hcoDgEoWWmX4cggams1hIUOij DOtO6eEfD1c9rW4v8ZiEEDQ3JVvHkoSfl+gHIrFwQx4n7bTNt2Zps5m3tN+cNYd6TxFb CqrH6OrvPc3IFSB+RsagU59aBJjSkHx1exBLK+9zsrANrTbz7o+FTFg955OlKmFFzGam BQyA== X-Gm-Message-State: AOAM533ewdDie73McygbY2o/zrf2fOsAKAIBvvgDezY3lA4n9aRERJdQ Tucv1Dp2tpLtdO3fWr8wrYHwadqXHJ+iomCW2xhHo2mtnl4= X-Google-Smtp-Source: ABdhPJxsBa8KV/DcxswJoSPrsszeS7ZqF/8OnJpWCil4w8MwgBOWEuaEHrXubDUvjCFVF+2jpycCVyiJekfOwVuCevg= X-Received: by 2002:a05:6e02:d8f:: with SMTP id i15mr2441590ilj.147.1599029662622; Tue, 01 Sep 2020 23:54:22 -0700 (PDT) MIME-Version: 1.0 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> <20200811120645.GA6199@alpha.franken.de> <20200826124646.GA9809@alpha.franken.de> In-Reply-To: <20200826124646.GA9809@alpha.franken.de> From: Huacai Chen Date: Wed, 2 Sep 2020 14:54:10 +0800 Message-ID: Subject: Re: [PATCH V3 1/2] MIPS: Loongson-3: Enable COP2 usage in kernel To: Thomas Bogendoerfer Cc: Jiaxun Yang , "open list:MIPS" , Fuxin Zhang , Zhangjin Wu Content-Type: text/plain; charset="UTF-8" Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Hi, Thomas, On Wed, Aug 26, 2020 at 8:48 PM Thomas Bogendoerfer wrote: > > On Fri, Aug 14, 2020 at 05:44:18PM +0800, Huacai Chen wrote: > > On Tue, Aug 11, 2020 at 8:08 PM Thomas Bogendoerfer > > wrote: > > > this comes with it's own memcpy/memset and stuff, I don't see a reason why > > > COP2 needs to be enabled there, > > gslq/gssq can also be generated by toolchains. > > I don't want to introduce every single CPU optimization bits into such > a closed first stage loader. So please use $(filter-out) in > arch/mips/boot/compressed/Makefile to disable creation of 16byte load/stores. > > > > 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. > > > > > THREAD_STATUS means thread_struct.cp0_status, which is the cp0_status > > when a process runs in kernel-space. KSTK_STATUS (what you have seen > > in copy_thread_tls() below) means cp0_status in a process's kernel > > stack, which saves the cp0_status when a process runs in user-space. > > Whether COP2 exception can work depends on that KSTK_STATUS (but not > > THREAD_STATUS) should not contain CU2 at the first time. So, whether > > or not THREAD_STATUS contains CU2, it won't break COP2 handling. > > so why don't we fix the the in-kernel cp0_status instead ? > > How about this ? > > diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c > index 90b869297893..26fb77a8d406 100644 > --- a/arch/mips/kernel/process.c > +++ b/arch/mips/kernel/process.c > @@ -133,6 +133,7 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long usp, > /* Put the stack after the struct pt_regs. */ > childksp = (unsigned long) childregs; > p->thread.cp0_status = read_c0_status() & ~(ST0_CU2|ST0_CU1); > + p->thread.cp0_status |= ST0_KERNEL_CUMASK; > if (unlikely(p->flags & PF_KTHREAD)) { > /* kernel thread */ > unsigned long status = p->thread.cp0_status; I tried this way but it doesn't work, the reason is that the resume routine in r4k_switch.S save the current hardware status into THREAD_STATUS, but CU2 in hardware is cleared in its caller (i.e., switch_to). However, I will send V5 to use ST0_KERNEL_CUMASK in all possible places to avoid #ifdefs. Huacai > > Thomas. > > -- > Crap can work. Given enough thrust pigs will fly, but it's not necessarily a > good idea. [ RFC1925, 2.3 ]