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=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 A13CCC433E2 for ; Fri, 28 Aug 2020 09:52:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 77F132098B for ; Fri, 28 Aug 2020 09:52:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728218AbgH1JwU (ORCPT ); Fri, 28 Aug 2020 05:52:20 -0400 Received: from mail-il1-f195.google.com ([209.85.166.195]:43562 "EHLO mail-il1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728016AbgH1JwS (ORCPT ); Fri, 28 Aug 2020 05:52:18 -0400 Received: by mail-il1-f195.google.com with SMTP id m1so344599ilj.10 for ; Fri, 28 Aug 2020 02:52:18 -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=1uAKjng0UIBlO6miYN7hfCf7HNVgfDf1UDVJW4y6fVw=; b=XbL4V/+5YZeWyVS19Q0rsWhfhjk/ddBoUUoO3n0l+30UOcDmraIRzjEjTwlpfQh1LD S5UfbfvgePJVzGwS9YRh+9z9QJtMTXKbKP6uxDoGPcdB1NbdIaDLBDq6opG9zcgrgfVN qsjvwlLHZIxeXrBPUI8juP7V0zZFteEEoOxDVDqFLfdBTAzgRlKrtyfcPzQV+vVKA2Do IVkScLPxWsl6jbaWA1t+H4Sf0r832I1PG4HTOnGN/TYgA+OqvCBK/3MlgbisM8qH+YZm WwjY5pU0yeMteqms+8Mz7VSsAzv6rrTlF5yxn7hkot9elS/PKsfwIoc/wgcI854GWK1R HyeA== X-Gm-Message-State: AOAM532RIvFVFWLv72wVU4v5e01ZT1HSIY0VJekuiAjX04Se+rOk2GDc 1haB6W893wPJT7gViT+dUDbYeIRGWpYpNPSs5Y5M6hjNNnGfQupN X-Google-Smtp-Source: ABdhPJy7EXzq/+Mg34/Q4JCbDjxRjpoB/Ui3bOO9zffnw5sk6OFgGAl7HqeSSbWzXn7SGJ9/jR4SlYJX0QwmfBArcYk= X-Received: by 2002:a05:6e02:cb0:: with SMTP id 16mr734734ilg.147.1598608337609; Fri, 28 Aug 2020 02:52:17 -0700 (PDT) MIME-Version: 1.0 References: <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> <20200828084242.GA6817@alpha.franken.de> <20200828093308.GA7888@alpha.franken.de> In-Reply-To: <20200828093308.GA7888@alpha.franken.de> From: Huacai Chen Date: Fri, 28 Aug 2020 17:52:05 +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 Fri, Aug 28, 2020 at 5:34 PM Thomas Bogendoerfer wrote: > > On Fri, Aug 28, 2020 at 05:21:19PM +0800, Huacai Chen wrote: > > Hi, Thomas, > > > > On Fri, Aug 28, 2020 at 4:43 PM Thomas Bogendoerfer > > wrote: > > > > > > On Thu, Aug 27, 2020 at 11:48:29AM +0800, Huacai Chen wrote: > > > > 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; > > > > This seems a good idea, I will send a new version. > > > > > > IMHO it migt be even better to just use > > > > > > p->thread.cp0_status = read_c0_status(); > > > > > > without masking. We are in kernel, so we took care of whatever CU1/CU2 > > > handling had to be done at kernel entry. So keeping the current cp0 status > > > for the new thread looks more sane to me. > > I think this may cause FPU be enabled in kernel by mistake. > > if it is enabled at that point, it was already enabled in kernel. In kernel FPU may be enabled temporarily, and it seems a preemptible kernel may enable FPU for a new process (maybe I'm wrong, this is a bit complex). Huacai > > Thomas. > > -- > Crap can work. Given enough thrust pigs will fly, but it's not necessarily a > good idea. [ RFC1925, 2.3 ]