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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 87904C433EF for ; Tue, 1 Mar 2022 16:48:54 +0000 (UTC) Received: from localhost ([::1]:38794 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nP5gD-00034X-7T for qemu-devel@archiver.kernel.org; Tue, 01 Mar 2022 11:48:53 -0500 Received: from eggs.gnu.org ([209.51.188.92]:59686) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nP5en-0002M3-FW for qemu-devel@nongnu.org; Tue, 01 Mar 2022 11:47:25 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:31984) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nP5ek-000737-9W for qemu-devel@nongnu.org; Tue, 01 Mar 2022 11:47:23 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1646153239; h=from:from:reply-to:reply-to:subject:subject: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=wKRx8J1v+P6Zds2BdUJ+SAjwMAKFC4V+Bu1chmcFujw=; b=BgKlrKCv+OC3koR9rQOTxrVxWXO/Fv5oOGw2qYB1JBWf8c3k6vzlCNIgLPPZxdzXaAb/PO C1PadZWVjrv8zqURpw0vr6GO/JghIOpHYROgnNcM8d/qVJVn9AV6c9WxI6Wm/soM+HXV6a cI6fD5x+/Dla03WMVy1v5mLdehmxWto= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-537-7v672GV6OUaD0VIBzrhyxw-1; Tue, 01 Mar 2022 11:47:11 -0500 X-MC-Unique: 7v672GV6OUaD0VIBzrhyxw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9D9B0800422; Tue, 1 Mar 2022 16:47:09 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.101]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DAB7886BA0; Tue, 1 Mar 2022 16:47:07 +0000 (UTC) Date: Tue, 1 Mar 2022 16:47:04 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Maydell Subject: Re: [PATCH v3 00/17] target/arm: Implement LVA, LPA, LPA2 features Message-ID: References: <20220223223137.114264-1-richard.henderson@linaro.org> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.1.5 (2021-12-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: alex.bennee@linaro.org, qemu-arm@nongnu.org, Richard Henderson , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Mar 01, 2022 at 04:30:30PM +0000, Peter Maydell wrote: > On Tue, 1 Mar 2022 at 16:28, Daniel P. Berrangé wrote: > > > > On Tue, Mar 01, 2022 at 04:16:25PM +0000, Peter Maydell wrote: > > > On Tue, 1 Mar 2022 at 16:08, Peter Maydell wrote: > > > > > > > > On Wed, 23 Feb 2022 at 22:31, Richard Henderson > > > > wrote: > > > > > > > > > > Changes for v3: > > > > > * Update emulation.rst. > > > > > * Split out separate update to ID_AA64MMFR0. > > > > > * Hack for avocado. > > > > > > > > > > If the avocado hack isn't acceptable, perhaps just drop the > > > > > last two patches for now? > > > > > > > > I think that given that there are Linux kernels out there > > > > that won't boot if LPA2 is enabled, we should probably have > > > > a -cpu command line option to disable it. Otherwise we might > > > > get a bunch of "why did my kernel stop booting" bug reports. > > > > > > ...and should using a versioned machine type also default > > > -cpu max to not enabling that? Not sure what x86 or other > > > precedent is there. > > > > I don't recall us coming across an important scenario where a guest > > would fail to boot when we /enable/ a given CPU feature on x86, > > requiring us to hide it from -cpu max/host. > > > > Assuming the QEMU/KVM implementation of a CPU feature is correct > > per the relevant spec, then artificially hiding it by default from > > -cpu max feels questionable, as that penalizes non-buggy guest OS. > > Yeah. It's just unfortunate that "buggy guest OS" here is > "every Linux up to 5.11". Lets say the lpa2 feature was tied so it only gets enabled in the new 7.0 machine type version, even if KVM/QEMU could supports it fine with any machine type version. If someone runs a VM with Linux 5.6 with -cpu max -machine virt' it is going to break. Our choice is then between telling them to change their QEMU config to -cpu max,-lpa2 -machine virt vs telling them to use -cpu max -machine virt-6.2 there's not much practical difference in those scenarios, for someone deploying a new VM instance. It would, however, benefit people who had already previously deployed a VM with QEMU using a explicit versioned machine type. This would be the case for anyone using libvirt, as libvirt always expands the user's config to be fully versioned. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|