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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 81670C2D0DB for ; Tue, 28 Jan 2020 12:35:06 +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 4E5F72064C for ; Tue, 28 Jan 2020 12:35:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Ig2tDdxJ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4E5F72064C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:58314 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iwQ5B-000220-KJ for qemu-devel@archiver.kernel.org; Tue, 28 Jan 2020 07:35:05 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:49329) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iwQ4Q-0001K7-EA for qemu-devel@nongnu.org; Tue, 28 Jan 2020 07:34:19 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iwQ4P-0007St-En for qemu-devel@nongnu.org; Tue, 28 Jan 2020 07:34:18 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:60452 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iwQ4P-0007SX-Bd for qemu-devel@nongnu.org; Tue, 28 Jan 2020 07:34:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1580214856; h=from:from: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=qYrr1r5HScc8LjsIpP5plCEtmmtVdUjtmM5ZorajYj4=; b=Ig2tDdxJa+I/Utn5vXAFJWRtw+t7coZKleTGKVPSmWEPbBUntJi5ABWAFAiBPUUX2HTMAV C57NfuW4Ip3OJfe2GvjHQBo5jeA66hnt7um5XrDPhKOFViCyKU+/VKvjQ8zZv9mE4kgym5 RjUW1Lb6zes6m527qmzUMCs3/8npKTw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-46-f3jAmo7PMRKPlP2m-0SE3A-1; Tue, 28 Jan 2020 07:34:13 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5310E800D48; Tue, 28 Jan 2020 12:34:12 +0000 (UTC) Received: from [10.36.116.37] (ovpn-116-37.ams2.redhat.com [10.36.116.37]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 21A6286E0E; Tue, 28 Jan 2020 12:34:09 +0000 (UTC) Subject: Re: [question] hw/arm/virt: about the default gic-version in accelerated mode To: Andrew Jones , Peter Maydell References: <20200128122915.ehzgj5kpmsw5azap@kamzik.brq.redhat.com> From: Auger Eric Message-ID: Date: Tue, 28 Jan 2020 13:34:06 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20200128122915.ehzgj5kpmsw5azap@kamzik.brq.redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-MC-Unique: f3jAmo7PMRKPlP2m-0SE3A-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 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: qemu-arm , qemu list , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Drew, On 1/28/20 1:29 PM, Andrew Jones wrote: > On Tue, Jan 28, 2020 at 10:52:50AM +0000, Peter Maydell wrote: >> On Tue, 28 Jan 2020 at 10:47, Auger Eric wrote: >>> When arm virt machine is run in accelerated mode with "-cpu host >>> -machine virt", the default gic version is 2. >>> >>> I understand the rationale with TCG where we don't have MSI ITS >>> emulation along with GICv3 so we need to choose GICv2 to get GICv2M >>> functionality. >>> >>> However in KVM mode, I would have expected to see the host GIC probed to >>> set the same version on guest. Indeed most of our HW now have GICv3 >>> without GICv2 compat mode so our default values lead to weird traces: >>> >>> " >>> qemu-system-aarch64: PMU: KVM_SET_DEVICE_ATTR: Invalid argument >>> qemu-system-aarch64: failed to set irq for PMU >>> " >>> >>> I would like to propose a patch to improve those errors and also suggest >>> a hint. But I also wanted to know whether you would accept to change the >>> default value with KVM and choose the host version instead of 2. For TCG >>> we would keep v2. >> >> As with the -cpu option, the default is there for command >> line backward compatibility primarily. Even if we had >> better support for MSI ITS emulation we'd still leave >> the default at GICv2. >> >> If you want "do the best you can, regardless of accelerator" >> that is "-cpu max -machine gic-version=max". >> > > There is a case where we can probe without breaking backward > compatibility. That case is kvm-enabled and no gic-version > specified. The reason it would be safe to probe the GIC version > is because unless the host was a gicv2 host, then that command > line wouldn't have worked anyway. Except if the host GICv3 has a GICv2 compat (which is pretty unlikely)? Eric And, if it is a gicv2 host, > then the probing will come to the same conclusion as the > default and nothing will have changed. > > Thanks, > drew > >