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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,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 8CA2CC433E9 for ; Mon, 22 Feb 2021 14:20:50 +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 1AC8764DB1 for ; Mon, 22 Feb 2021 14:20:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1AC8764DB1 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.88105.165529 (Exim 4.92) (envelope-from ) id 1lEC4Z-0001MX-Mh; Mon, 22 Feb 2021 14:20:27 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 88105.165529; Mon, 22 Feb 2021 14:20:27 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lEC4Z-0001MQ-JF; Mon, 22 Feb 2021 14:20:27 +0000 Received: by outflank-mailman (input) for mailman id 88105; Mon, 22 Feb 2021 14:20:26 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lEC4Y-0001MK-DL for xen-devel@lists.xenproject.org; Mon, 22 Feb 2021 14:20:26 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id b9c3f9c7-c2d7-44d5-854d-fa3691615cd1; Mon, 22 Feb 2021 14:20:25 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id DDC39AE04; Mon, 22 Feb 2021 14:20:24 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: b9c3f9c7-c2d7-44d5-854d-fa3691615cd1 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1614003625; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=b0Jl9Bcg7pqGHTTJc5Uzuuj9YDW7llrK2+vjY5FAdrE=; b=YeDaQco3Mod0WzCZw8DIG6oTDohnVjzSDVqdZIM8+dWYCf1l8Rs3TPK2hlhFDwSRBDA7r+ jt7z1brz01gjyMCp2eMJdxo0kilKh4C6EdMB8Di8cn1YbUCYnc7t6udZ7ZMFbnYkCE/jf7 fPPAwP4TObF24O5VRvzwYeAsShi/CkE= Subject: Re: [PATCH][4.15] x86: mirror compat argument translation area for 32-bit PV To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Wei Liu , Ian Jackson References: From: Jan Beulich Message-ID: Date: Mon, 22 Feb 2021 15:20:24 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit On 22.02.2021 15:13, Roger Pau Monné wrote: > On Mon, Feb 22, 2021 at 12:35:21PM +0100, Roger Pau Monné wrote: >> On Mon, Feb 22, 2021 at 11:27:07AM +0100, Jan Beulich wrote: >>> Now that we guard the entire Xen VA space against speculative abuse >>> through hypervisor accesses to guest memory, the argument translation >>> area's VA also needs to live outside this range, at least for 32-bit PV >>> guests. To avoid extra is_hvm_*() conditionals, use the alternative VA >>> uniformly. >> >> Since you are double mapping the per-domain virtual area, won't it >> make more sense to map it just once outside of the Xen virtual space >> area? (so it's always using PML4_ADDR(511)) > > Right, that's not possible for PV 64bit domains because it's guest > owned linear address space in that case. > > It seems like paravirt_ctxt_switch_to will modify the root_pgt to set > the PERDOMAIN_VIRT_START entry, does the same need to be done for > PERDOMAIN2_VIRT_START? I don't think so, no. Argument translation doesn't happen when the restricted page tables are in use, and all other uses of the per-domain area continue to use the "normal" VA. > I would also consider giving the slot a more meaningful name, as > PERDOMAIN2_VIRT_START makes it seem like a new per-domain scratch > space, when it's just a different mapping of the existing physical > memory. > > Maybe PERDOMAIN_MIRROR_VIRT_START? Or PERDOMAIN_XLAT_VIRT_START? XLAT would be too specific - while we use it for xlat only, it's still all of the mappings that appear at the alternate addresses. I did consider using MIRROR, but it got too long for my taste. Now that I think about it maybe PERDOMAIN_ALT_VIRT_START would do? Jan