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=-18.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=ham 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 1904CC433ED for ; Thu, 22 Apr 2021 19:02:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CF95D613F0 for ; Thu, 22 Apr 2021 19:02:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238142AbhDVTDR (ORCPT ); Thu, 22 Apr 2021 15:03:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40708 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236058AbhDVTDQ (ORCPT ); Thu, 22 Apr 2021 15:03:16 -0400 Received: from mail-pf1-x42b.google.com (mail-pf1-x42b.google.com [IPv6:2607:f8b0:4864:20::42b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 58F44C06174A for ; Thu, 22 Apr 2021 12:02:41 -0700 (PDT) Received: by mail-pf1-x42b.google.com with SMTP id 10so23487623pfl.1 for ; Thu, 22 Apr 2021 12:02:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=dDg1aD567r790FBm59yB32VSiEfP4a8Vhdm7ZOlyWSE=; b=euriQQ4HYSFTyle9ZIz/Kj+95qPHjc2RZKOpm3tx0GJHl/9ATsgit+ukV1RHMcsY+o VgcXzxUWzvwNiNMDlkacK9TYjHIlgQ5l7gRHNTCXoKNiyqKvuTSD8/tGVxYqsuFJIoh8 xewigEVoIBgO1oy8w/w0xAWDmlZk9uwJYVRStiGpW2DMuqgNz3y7Y6Qc7Ks4gT0TVF9L CeT0d/7onAzaaPsTeMFZeC3xaVyRUEOY2n//UXefJuaXEptg09gzeXyhiv3n8jPQ9qyQ qlLhA3VpG8NM42Y8DrIUy3f90XGk8N7XBLm0CW3ZiFUWUK98Kf85Zp784WBU3pt1T3VR YaBg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=dDg1aD567r790FBm59yB32VSiEfP4a8Vhdm7ZOlyWSE=; b=g2YCQ3D58/eBn5szneM8BgAbXfVkf+lwb6LKpt/1cTxP1uBSYaL1advxi8CQ06IxFC ryYDFjQBlLh83Nu9MXvw+erXlBdFJeN1Y1Sf6pnkmUXkjOS5SNUsDUEq5WxLIrh+X8LC EV8L2aGVeW+mIgCzv1+e+M9mRH2NHb37AXyhWKUzKONwlO+4DyYeJfHBHEReyGXMKG+9 K+qmaz7rUi3DPMYwT8inMIXNe/OI8pqYOWOLjp5CmoSLXMTQNNFepdzxhMTYandO7itc PPcHGTYNiwi26a03Ux7igOEiNFwfTtpuP85EQS3cnZrOpMbumIYeSuoJIKsZbwzk9xaJ kTPA== X-Gm-Message-State: AOAM531Kez3lxsIM3fbQaFLclBTxYc5Z7BmzJDLesHoA06d+VH71TZdK cj2ZVr3P1tug73CciJPAypsWQxYB6DwtAqjKm4SliQ== X-Google-Smtp-Source: ABdhPJzu+LO3Vq6UjOF9vfqE0F/kGHQOn08KBci7pvBqj26HJBSZceKpfo1pqUr72AxVxlJW2tbmIhRvhi1UB74GV8I= X-Received: by 2002:aa7:91d1:0:b029:1fe:2a02:73b9 with SMTP id z17-20020aa791d10000b02901fe2a0273b9mr81424pfa.2.1619118160718; Thu, 22 Apr 2021 12:02:40 -0700 (PDT) MIME-Version: 1.0 References: <20210422001736.3255735-1-seanjc@google.com> In-Reply-To: <20210422001736.3255735-1-seanjc@google.com> From: Reiji Watanabe Date: Thu, 22 Apr 2021 12:02:24 -0700 Message-ID: Subject: Re: [PATCH v2] KVM: SVM: Delay restoration of host MSR_TSC_AUX until return to userspace To: Sean Christopherson Cc: Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org @@ -2893,12 +2882,15 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) return 1; /* - * This is rare, so we update the MSR here instead of using - * direct_access_msrs. Doing that would require a rdmsr in - * svm_vcpu_put. + * TSC_AUX is usually changed only during boot and never read + * directly. Intercept TSC_AUX instead of exposing it to the + * guest via direct_acess_msrs, and switch it via user return. */ 'direct_acess_msrs' should be 'direct_access_msrs'. svm->tsc_aux = data; - wrmsrl(MSR_TSC_AUX, svm->tsc_aux); + + preempt_disable(); + kvm_set_user_return_msr(TSC_AUX_URET_SLOT, data, -1ull); + preempt_enable(); break; One of the callers of svm_set_msr() is kvm_arch_vcpu_ioctl(KVM_SET_MSRS). Since calling kvm_set_user_return_msr() looks unnecessary for the ioctl case and makes extra things for the CPU to do when the CPU returns to userspace for the case, I'm wondering if it might be better to check svm->guest_state_loaded before calling kvm_set_user_return_msr() here. The patch looks good to me other than those two minor things. Thanks, Reiji