From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.0 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 323547D2EF for ; Wed, 29 May 2019 01:25:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725860AbfE2BZm (ORCPT ); Tue, 28 May 2019 21:25:42 -0400 Received: from mail-wr1-f68.google.com ([209.85.221.68]:34799 "EHLO mail-wr1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725855AbfE2BZm (ORCPT ); Tue, 28 May 2019 21:25:42 -0400 Received: by mail-wr1-f68.google.com with SMTP id f8so475686wrt.1 for ; Tue, 28 May 2019 18:25:41 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=rqj4DN+mKFOFN2ElIEBtWrUBDtgBpL5CxV4R4XTM10o=; b=nJrYDY/NEnyvv7sm8SqXPyv+RhyARg/NgpgqZteM1uejUtYod0n5Q5CWVpREkqOE7g Qi8t5XxEx4mVp7a7RO390+BnE5Zj9D5td6XSLyLyP1MNtht/7Ci+kQ0CBZJOui/VJq2k XPWwo4WUvTlC8InyPpGcd7YDV+dr5J6gFqp9GeOj7TO5z4SnU5w+827XQEASEwmB8nLh 1BrA2+1xSlowZ2OtIfhD6tR+oc696Ia/1wOjeatTXvgmepbxVzgJNZNvYApMpoUrkXSV TkN9mmvrON2vg6xbghLRnswLe4nNGV/iGAkWqg9/ewUg6lt+tUoCWEGcNl3h1Y5V4Yhh OkxA== X-Gm-Message-State: APjAAAWpcu/MpRf9rgm9es746i3OCXn/LYkJ1+0HqbD9OjhZEhCebRpw EFJ9bWj4XDmOV+qfz5zDgwT0sw== X-Google-Smtp-Source: APXvYqwtWVxxE2Y3KBugsv4RW0JNUGuXKYKlfAWL8wp283sVlUi5mkh0LOf0h0ykT1V8TpWOn1NBog== X-Received: by 2002:a5d:5189:: with SMTP id k9mr14487648wrv.329.1559093141154; Tue, 28 May 2019 18:25:41 -0700 (PDT) Received: from [192.168.10.150] ([93.56.166.5]) by smtp.gmail.com with ESMTPSA id s15sm10845265wrn.68.2019.05.28.18.25.39 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 28 May 2019 18:25:40 -0700 (PDT) Subject: Re: [PATCH v2 1/3] KVM: x86: add support for user wait instructions To: Peter Zijlstra , Tao Xu Cc: rkrcmar@redhat.com, corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, sean.j.christopherson@intel.com, x86@kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, jingqi.liu@intel.com References: <20190524075637.29496-1-tao3.xu@intel.com> <20190524075637.29496-2-tao3.xu@intel.com> <20190527103003.GX2623@hirez.programming.kicks-ass.net> From: Paolo Bonzini Message-ID: Date: Wed, 29 May 2019 03:25:39 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190527103003.GX2623@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 27/05/19 12:30, Peter Zijlstra wrote: >> This patch adds support for UMONITOR, UMWAIT and TPAUSE instructions >> in kvm, and by default dont't expose it to kvm and provide a capability >> to enable it. > > I'm thinking this should be conditional on the guest being a 1:1 guest, > and I also seem to remember we have bits for that already -- they were > used to disable paravirt spinlocks for example. This should be userspace's choice. It would indeed be silly to enable this while overcommitted, but KVM doesn't really care. Paolo