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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 869BFC433DB for ; Thu, 11 Mar 2021 17:27:17 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id A82C864DD1 for ; Thu, 11 Mar 2021 17:27:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A82C864DD1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:51650 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lKP5f-00057Y-Fo for qemu-devel@archiver.kernel.org; Thu, 11 Mar 2021 12:27:15 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:33878) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lKOvq-0004UL-Pu; Thu, 11 Mar 2021 12:17:08 -0500 Received: from mx2.suse.de ([195.135.220.15]:37818) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lKOvl-0007um-5c; Thu, 11 Mar 2021 12:17:06 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 4155BAB8C; Thu, 11 Mar 2021 17:16:58 +0000 (UTC) Subject: Re: arm: "max" CPU class hierarchy changes possible? To: Paolo Bonzini , Peter Maydell References: <11e9d3bb-c94c-4ad7-35b0-b698376c5e00@suse.de> <2e6a5d98-e022-0b39-5f30-92eb74491d3b@redhat.com> From: Claudio Fontana Message-ID: <2277fdf5-ec92-476a-8fe5-0d4eee23dfef@suse.de> Date: Thu, 11 Mar 2021 18:16:52 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <2e6a5d98-e022-0b39-5f30-92eb74491d3b@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=195.135.220.15; envelope-from=cfontana@suse.de; helo=mx2.suse.de X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-arm , qemu-devel , Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/11/21 5:18 PM, Paolo Bonzini wrote: > On 11/03/21 16:02, Peter Maydell wrote: >> On Thu, 11 Mar 2021 at 14:27, Claudio Fontana wrote: >>> the "max" cpu in x86 and s390 is a class, >>> >>> and then "host" has "max" as parent. >>> >>> This would be a convenient setup for ARM too, as it would allow to put common code between kvm and tcg in the "max" class, >>> and allow "host" to specialize the behavior for KVM (and in the future HVF probably). >>> >>> Would changing the class hierarchy this way be acceptable, cause any problems? >> >> It's not clear to me why 'host' would be a subtype of 'max': >> that doesn't seem like an obvious relationship. > > On x86, "-cpu host" is essentially the same as "-cpu max" with the only > difference that it errors out on TCG. So: > > - with TCG: "-cpu max" enables all that can be emulated, "-cpu host" fails > > - with KVM: "-cpu max" enables all that can be virtualized, "-cpu host" > does the same > > Paolo > Maybe Peter you could clarify similarly what the intended meaning of "max" is on ARM? TCG: for aarch64, the starting point seems to be Cortex-A57, and then lots of other features are added on top of it, and for non-aarch64, the starting point seems to be Cortex-A15, plus "old-style VFP short-vector support". Is the intention to enable all that can be emulated here too, like for X86? KVM: (aarch64-only): aarch64_max_initfn(): The following comment in the code seems wrong to me: /* -cpu max: if KVM is enabled, like -cpu host (best possible with this host); */ This is not exactly true: "-cpu max" calls kvm_arm_set_cpu_features_from_host(), (which checks "dtb_compatible", and if not set gets the features from the host, if set ...?) After that, calls aarch64_add_sve_properties() and then adds also "svw-max-vq". This code is common with TCG. In the case of cpu host instead, "-cpu host" calls kvm_arm_set_cpu_features_from_host(), same as max, then calls aarch64_add_sve_properties() but does NOT add "svw-max-vq". Is this a bug? Are "max" and "host" for KVM supposed to be the same like with x86? Thanks, Claudio