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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 A4250C433DB for ; Mon, 22 Mar 2021 15:47:38 +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 346076198D for ; Mon, 22 Mar 2021 15:47:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 346076198D 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]:60400 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lOMmH-0006QA-BF for qemu-devel@archiver.kernel.org; Mon, 22 Mar 2021 11:47:37 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:38350) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lOMir-0003Le-5Q for qemu-devel@nongnu.org; Mon, 22 Mar 2021 11:44:05 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:31928) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lOMio-0006P9-L1 for qemu-devel@nongnu.org; Mon, 22 Mar 2021 11:44:04 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1616427841; 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=EDJemio96d8tkoZ6jV/4FbNdtDb7eGAaj0+0SsP6A8Y=; b=E+EY72y2R47Ib15l42o68HHh7RfDRsF42Q4fp+1UdW+lA0JLz6SVr/kxba/tyOnbBguciV wQUGnMDh1Eu4sBfbaU80fuotgid1O734XzGPQLTi0qaqHNS+83mLkN2zjQRqB43cDkpZ/b PJg2f1wHJfSTV6BfbeLKGfe6Xopa+sg= 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-370-ED0fzuqpOAWBk7JqJM4ddw-1; Mon, 22 Mar 2021 11:42:30 -0400 X-MC-Unique: ED0fzuqpOAWBk7JqJM4ddw-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 1DDF38018A1; Mon, 22 Mar 2021 15:42:29 +0000 (UTC) Received: from harajuku.usersys.redhat.com (unknown [10.40.195.160]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4663C60BE5; Mon, 22 Mar 2021 15:42:25 +0000 (UTC) Message-ID: <4b35e1dc2c6a2af117542eca6571ddf1e261fe10.camel@redhat.com> Subject: Re: [PATCH 0/3] target/arm: Add nested virtualization support From: Andrea Bolognani To: Haibo Xu , qemu-devel@nongnu.org, qemu-arm@nongnu.org Date: Mon, 22 Mar 2021 16:42:23 +0100 In-Reply-To: References: User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=abologna@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=abologna@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H4=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: peter.maydell@linaro.org, drjones@redhat.com, philmd@redhat.com, richard.henderson@linaro.org, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 2021-03-22 at 10:07 +0000, Haibo Xu wrote: > This series add support for ARMv8.3/8.4 nested virtualization support > in KVM mode. It's based on Marc Zyngier's kernel KVM patches[1], and > has been tested on a FVP model to run a L2 guest with Qemu. Now the > feature can be enabled by "-M virt,accel=kvm,virtualization=on" when > starting a VM. Why the need to enable this explicitly? AFAIK, that's not necessary for any other architecture: on x86, you just need to make sure you're using '-cpu host' and pass a parameter to the kernel module. Even assuming this can't be enabled transparently, wouldn't its availability it be controlled by a CPU feature flag, similar to what already happens for SVE and PMU, rather than a machine type option? That would also address the discoverability issue: unless I'm mistaken (which I very well might be :), with the current implementation there's no way to tell whether nested KVM will be usable short of trying and seeing whether QEMU errors out. -- Andrea Bolognani / Red Hat / Virtualization