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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 31E94C3815B for ; Mon, 20 Apr 2020 10:23:12 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id CE6A321473 for ; Mon, 20 Apr 2020 10:23:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="qhaqpqFB" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CE6A321473 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=o+aNeY7N9iU0rKnFYkHk6m3E+KbJmTHX+Xg2/0R0yTk=; b=qhaqpqFB/JKgTJ wLrlYRtM4mU6K0CH+iHtKsdmekx3o22XVYY9Ans2hLkc6C++xh9MYY5AFcc62QJbHtKmIemlz3D8e 7ndkaXUFcnuKDx4Nau6ye/0uR0+Vzkk0HudyJtWXLAws2pYvwSfWbpSchiEQz51myNUY4QSW5mnVn RlXxwlALC6dsxDmBatAuJxYmfHSOAgBqe4xaGQyPqVN9Gcwvas93m3IgJYbNTuvBKiK2mM4IBgG65 +FXzjGc11oUFcP3lNwhK+K4gBt1R4hbHGer731vHZMgnd98SS77YWIZdhIqH1KML8nbcjtpbi1P0A jQtUEYtR2Q2k3Cs+eDfw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jQTa0-0003F5-B6; Mon, 20 Apr 2020 10:23:08 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jQTZw-0003E3-Oh for linux-arm-kernel@lists.infradead.org; Mon, 20 Apr 2020 10:23:06 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id A185868C4E; Mon, 20 Apr 2020 12:22:59 +0200 (CEST) Date: Mon, 20 Apr 2020 12:22:59 +0200 From: Christoph Hellwig To: James Morse Subject: Re: stop messing with set_fs in arm_sdei Message-ID: <20200420102259.GA7862@lst.de> References: <20200414142302.448447-1-hch@lst.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200420_032304_952900_AEADF886 X-CRM114-Status: GOOD ( 16.37 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Christoph Hellwig , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Apr 14, 2020 at 04:59:16PM +0100, James Morse wrote: > Hi Christoph, > > On 14/04/2020 15:23, Christoph Hellwig wrote: > > can you take a look at this series? I've been trying to figure out > > what the set_fs in arm_sdei is good for, and could not find any > > good reason. But I don't have any hardware implementing this interface, > > so the changes are entirely untested. > > Its a firmware thing, think of it as a firmware assisted software NMI. > > The arch code save/restores set_fs() because the entry code does that when taking an > exception from EL1. SDEI does the same because it doesn't come via the same entry code. It > does it in C because that C is always run before the handler, something that isn't true > for the regular assembly version. > > The regular entry code does this because any exception may have interrupted code that had > addr_limit set to something else: > https://bugs.chromium.org/p/project-zero/issues/detail?id=822 > > and the patch that fixed it: commit e19a6ee2460b "arm64: kernel: Save and restore UAO and > addr_limit on exception entry" Can you throw in a comment documenting this better? And pick up the first patch while we're at it - no need to expose such low-level mechanisms to modules. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel