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=unavailable 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 2AECCC433B4 for ; Thu, 22 Apr 2021 19:02:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E691761424 for ; Thu, 22 Apr 2021 19:02:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238666AbhDVTDS (ORCPT ); Thu, 22 Apr 2021 15:03:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40710 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236287AbhDVTDQ (ORCPT ); Thu, 22 Apr 2021 15:03:16 -0400 Received: from mail-pf1-x435.google.com (mail-pf1-x435.google.com [IPv6:2607:f8b0:4864:20::435]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 69059C061756 for ; Thu, 22 Apr 2021 12:02:41 -0700 (PDT) Received: by mail-pf1-x435.google.com with SMTP id m11so32388966pfc.11 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=AumGMgcNLr7VABLWNyRKXbCsXWDSTKPdVcpivaLlG8+Nptgip8KB3jreqsYnZ0p+y/ JvD0wXw+hvlHvpQJOXzUnqH/dbYIMOBFGigvEdZubfbRPLGg0WgJ5HzQKw+HlFKqB/ht bPqe957lbMgk3gMJeZRz/M2QhGOWKSYJDT6B72zY3nnk6nv6PYcYozs31a+jYK6n6yWp KTuq1m5sxb8UXmJ717vAXWhMg0l/QcfR5xj119DjumJus6c29JYJ/RrXfSYhb159y0qV Q1vKFNZ1BFrre97D+faoGmIVf/CwjG87JlNqU9Bi1qW5QAaMyAmE24PxLMCelo/pthHU RHtw== X-Gm-Message-State: AOAM532vP0HAIFjWVkafIZm5v9HIduJ5Umq2AZXG2xGtTa15njCmEuR2 8HDCFgMpL02nCX3Tsm4SkhzY7neGPoIJ2IiSbkGegw== 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: linux-kernel@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