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=-6.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 BA947C433DB for ; Thu, 4 Feb 2021 10:56:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 80EF864F5E for ; Thu, 4 Feb 2021 10:56:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235462AbhBDK4K (ORCPT ); Thu, 4 Feb 2021 05:56:10 -0500 Received: from mail.kernel.org ([198.145.29.99]:53362 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235378AbhBDK4F (ORCPT ); Thu, 4 Feb 2021 05:56:05 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 4EB3864F72 for ; Thu, 4 Feb 2021 10:55:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1612436124; bh=iVOYJyr/gInCGMuwQ7LepyUha9WX21AN5d8OqnfR7uU=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=qOtWVjpEAiUSSLXsoyrSjnKcWA56wnfg5Z7L2v++SB2a/rhBNl35GlYhtDkYPZjJs 7nNyhWIpMTk/fZicthRrKes4oM5F0J6Y9h3laweFtq3sMd9y9eVUTp7Jj7eZUaLsIQ OngZ53jrn6HBCpW89NXpIViLkoUR/Rfz2oWZ3RoffC8E4CoKwZGqHVxWQh4I6f8JKV LDQb09+nmK5gwOQ3daMw7Zo+JhfmemRyN7J/IQfjSFMLqtoG4qmfhN06tWoXV857nY y0YZDJ3rIBwEoTrHDx/whsFqIEKBybxM1pV2OpfXjqvy5+JJn8FJ42pOHaX2hBWkvn ODr4iHhIVY2ig== Received: by mail-oi1-f171.google.com with SMTP id u66so1329548oig.9 for ; Thu, 04 Feb 2021 02:55:24 -0800 (PST) X-Gm-Message-State: AOAM530ey3b3zl6GdAkwfLjOK53kxfXUsXi1WvGHWTmMLaCIdi4v7uJF nUzVPppC1+NgZK5ISPcY96+7CnugfZd6FIhC9CI= X-Google-Smtp-Source: ABdhPJw4JbNRArUMkqNa7P08Ruf3Tr/UdRMkHpqxhSV9cSbnh0Qa9NdrQXiRZyzMr7GGmJreApH8hXm7DEY/6Qfy3lc= X-Received: by 2002:aca:ea0b:: with SMTP id i11mr4914161oih.33.1612436123393; Thu, 04 Feb 2021 02:55:23 -0800 (PST) MIME-Version: 1.0 References: <601b773a.1c69fb81.9f381.a32a@mx.google.com> <6c65bcef-d4e7-25fa-43cf-2c435bb61bb9@collabora.com> <20210204100601.GT1463@shell.armlinux.org.uk> <20210204104714.GU1463@shell.armlinux.org.uk> In-Reply-To: <20210204104714.GU1463@shell.armlinux.org.uk> From: Ard Biesheuvel Date: Thu, 4 Feb 2021 11:55:12 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: next/master bisection: baseline.login on rk3288-rock2-square To: Russell King - ARM Linux admin , Marc Zyngier Cc: Guillaume Tucker , Geert Uytterhoeven , Linux Kernel Mailing List , Linus Walleij , Linux ARM , Nicolas Pitre , "kernelci-results@groups.io" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (cc Marc) On Thu, 4 Feb 2021 at 11:48, Russell King - ARM Linux admin wrote: > > On Thu, Feb 04, 2021 at 11:27:16AM +0100, Ard Biesheuvel wrote: > > Hi Russell, > > > > If Guillaume is willing to do the experiment, and it fixes the issue, > > it proves that rk3288 is relying on the flush before the MMU is > > disabled, and so in that case, the fix is trivial, and we can just > > apply it. > > > > If the experiment fails (which would mean rk3288 does not tolerate the > > cache maintenance being performed after cache off), it is going to be > > hairy, and so it will definitely take more time. > > > > So in the latter case (or if Guillaume does not get back to us), I > > think reverting my queued fix is the only sane option. But in that > > case, may I suggest that we queue the revert of the original by-VA > > change for v5.12 so it gets lots of coverage in -next, and allows us > > an opportunity to come up with a proper fix in the same timeframe, and > > backport the revert and the subsequent fix as a pair? Otherwise, we'll > > end up in the situation where v5.10.x until today has by-va, v5.10.x-y > > has set/way, and v5.10y+ has by-va again. (I don't think we care about > > anything before that, given that v5.4 predates any of this) > > I'm suggesting dropping your fix (9052/1) and reverting > "ARM: decompressor: switch to by-VA cache maintenance for v7 cores" > which gets us to a point where _both_ regressions are fixed. > I understand, but we don't know whether doing so might regress other platforms that were added in the mean time. > I'm of the opinion that the by-VA patch was incorrect when it was > merged (it caused a regression), and it's only a performance > improvement. It is a correctness improvement, not a performance improvement. Without that change, the 32-bit ARM kernel cannot boot bare metal on platforms with a system cache such as 8040 or SynQuacer, and can only boot under KVM on such systems because of the special handling of set/way instructions by the host. The performance issue related to set/way ops under KVM was already fixed by describing data and unified caches as 1 set and 1 way when running in 32-bit mode. > Our attempts so far to fix it are just causing other > regressions. So, I think it is reasonable to revert both back to a > known good point which has worked over a decade. If doing so causes > regressions (which I think is unlikely), then that would be unfortunate > but alas is a price that's worth paying to get back to a known good > point - since then we're not stacking regression fixes on top of other > regression fixes. > This is exactly why I am proposing to queue the revert of the original patch for v5.12, and only backport it to v5.10 and v5.11 once we are sure it does not break anything else.