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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 70EFAC433E0 for ; Fri, 29 May 2020 10:59:58 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 40E2D207F5 for ; Fri, 29 May 2020 10:59:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=xen.org header.i=@xen.org header.b="dOwn4Yfu" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 40E2D207F5 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jecjs-0002xv-NX; Fri, 29 May 2020 10:59:48 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jecjr-0002xm-NR for xen-devel@lists.xenproject.org; Fri, 29 May 2020 10:59:47 +0000 X-Inumbo-ID: 82a9e16e-a19b-11ea-81bc-bc764e2007e4 Received: from mail.xenproject.org (unknown [104.130.215.37]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 82a9e16e-a19b-11ea-81bc-bc764e2007e4; Fri, 29 May 2020 10:59:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=bsXupUX5CAQgLcEwi1O7VUnO+wqZMFdhDU3R/Md8S0o=; b=dOwn4Yfuko8rcl2gDNiGLd7fGg DiJGnSfUpT9YfAaQBFix7Qel1jNWJVTz/Y8z7QvuVSxjx5JmmsvKAMZM9YuSzwcNdjT+FTCN9aZk6 keGQjhOxuxIVeKl/YR/Ct8E6yhzdC7XSGg3EDw5bfXz7jNiRpS/KQGazWQ+o2cjHY8X8=; Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jecjo-0001hr-3p; Fri, 29 May 2020 10:59:44 +0000 Received: from [54.239.6.188] (helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1jecjn-0005qx-Si; Fri, 29 May 2020 10:59:44 +0000 Subject: Re: [RFC PATCH 1/1] xen: Use a global mapping for runstate To: Jan Beulich References: <03e7cd740922bfbaa479f22d81d9de06f718a305.1590675919.git.bertrand.marquis@arm.com> From: Julien Grall Message-ID: <43781f37-184d-3ac8-8997-0a9be1de05ce@xen.org> Date: Fri, 29 May 2020 11:59:40 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Stefano Stabellini , Wei Liu , "paul@xen.org" , Andrew Cooper , "Xia, Hongyan" , Ian Jackson , George Dunlap , Bertrand Marquis , xen-devel@lists.xenproject.org, nd@arm.com, Volodymyr Babchuk , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" Hi Jan, On 29/05/2020 08:35, Jan Beulich wrote: > On 28.05.2020 20:54, Julien Grall wrote: >> On 28/05/2020 16:25, Bertrand Marquis wrote: >>> At the moment on Arm, a Linux guest running with KTPI enabled will >>> cause the following error when a context switch happens in user mode: >>> (XEN) p2m.c:1890: d1v0: Failed to walk page-table va 0xffffff837ebe0cd0 >>> >>> This patch is modifying runstate handling to map the area given by the >>> guest inside Xen during the hypercall. >>> This is removing the guest virtual to physical conversion during context >>> switches which removes the bug >> >> It would be good to spell out that a virtual address is not stable. So >> relying on it is wrong. > > Guests at present are permitted to change the mapping underneath the > virtual address provided (this may not be the best idea, but the > interface is like it is). Well yes, it could be point to data used by the userpsace. So you could corrupt a program. It is not very great. So I would be ready to accept such restriction on Arm at least because KPTI use case is far more concerning that a kernel trying to change the location of the runstate in physical memory. Cheers, -- Julien Grall