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=-8.7 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_PASS,URIBL_BLOCKED,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 AB14BC43387 for ; Tue, 8 Jan 2019 17:19:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7CCC12070B for ; Tue, 8 Jan 2019 17:19:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="cxZvZiiq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728590AbfAHRTo (ORCPT ); Tue, 8 Jan 2019 12:19:44 -0500 Received: from mail-it1-f194.google.com ([209.85.166.194]:35425 "EHLO mail-it1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727484AbfAHRTo (ORCPT ); Tue, 8 Jan 2019 12:19:44 -0500 Received: by mail-it1-f194.google.com with SMTP id p197so7061776itp.0 for ; Tue, 08 Jan 2019 09:19:43 -0800 (PST) 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=Zpa2fL7q2YZTofq9H0F49nWh5nPFN0Bl9DMZ4qDyzi8=; b=cxZvZiiqvt5CbEYPCEFQ65p+1B3pprinpPzF0PdVI+SQwvkKXidk3R9GBFec3EBXOG looVJcRTokGt2rmKessd1x48pAZfXc/oyqe0rLNguuE7UP8KZXQdfnq2Ec3oYN/z8aoZ za/k9/GmJj5ve/Ca6wG7oAW46b3EGCsY+o4X0/xHZXGG8wpKi4VYlXA7DYe9NDqfcF8X ZJaA4iOUCV31JBOy8EKyyGv961qKGEdQMaox0OCetrMH8J4HISGFmGOXYJsRCpXGtTmW Ewj3Jd5FvO9/f/guObVTOHdvysCFzrMb44Rr3vSfE4NIB5NYOCNjNQE0UXrjjo4ldzQM 0waQ== 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=Zpa2fL7q2YZTofq9H0F49nWh5nPFN0Bl9DMZ4qDyzi8=; b=r5CtftsBpDk7JSOavc2aFd+AbwrRgczt8S1gj8WCsuD9KeKHxec86qVHP/3Skqu0Ye 4brY3OfZceiR3qbOlTurFZH02prV03WkcPJ0JIkFxZEGryINGcg23PPS6JBnRXiJlm5c 3KWPSII7RfWSIKdmDtPHm12l/Ip7IM545hWrN7vJlmzeBawzbQCC0U2g1AlixWuC6AXK V6IUDXL0GCmVcxPxi4HbBioaCq2vUSPBRzKw9DBPtOju31zFNtGZBxQLz71l4pyuKfxr X3TnYa8qduvbzfooxXFiq5TDVpIODIn8c7g5F5OHLMFhE9XKunVimdiEHsBMvjziuMYA 15dg== X-Gm-Message-State: AJcUukfV5UOEG/AaAQJC/Kolhy9y+/smL7g7LEDpzsRiOg6e/1WoPT5h plLaVqHgzSR6qn9eK4RgoWLic7NB8fTNbHM49a9lCw== X-Google-Smtp-Source: ALg8bN6Ou/5/xF0tY5jUcJTvLf6IctdCv0epIHr4OrR571e81CpaZEmznhbtmqhgePpt4eVAybK2QqxTe3LusJPZvgs= X-Received: by 2002:a24:4a95:: with SMTP id k143mr1803645itb.77.1546967982815; Tue, 08 Jan 2019 09:19:42 -0800 (PST) MIME-Version: 1.0 References: <1545816338-1171-1-git-send-email-wei.w.wang@intel.com> <1545816338-1171-6-git-send-email-wei.w.wang@intel.com> <5C2DC132.9050103@intel.com> <5C3318A1.9090009@intel.com> <20190107182012.GL6118@tassilo.jf.intel.com> <5C34570D.6010208@intel.com> In-Reply-To: <5C34570D.6010208@intel.com> From: Jim Mattson Date: Tue, 8 Jan 2019 09:19:31 -0800 Message-ID: Subject: Re: [PATCH v4 05/10] KVM/x86: expose MSR_IA32_PERF_CAPABILITIES to the guest To: Wei Wang Cc: Andi Kleen , LKML , kvm list , Paolo Bonzini , Peter Zijlstra , Kan Liang , Ingo Molnar , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , like.xu@intel.com, Jann Horn , arei.gonglei@huawei.com Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 7, 2019 at 11:48 PM Wei Wang wrote: > > On 01/08/2019 02:48 AM, Jim Mattson wrote: > > On Mon, Jan 7, 2019 at 10:20 AM Andi Kleen wrote: > >>> The issue is compatibility. Prior to your change, reading this MSR > >>> from a VM would raise #GP. After your change, it won't. That means > >>> that if you have a VM migrating between hosts with kernel versions > >>> before and after this change, the results will be inconsistent. In the > >> No it will not be. All Linux kernel uses of this MSR are guarded > >> by a CPUID check. > > Linux usage is irrelevant to the architected behavior of the virtual > > CPU. According to volume 4 of the SDM, this MSR is only supported when > > CPUID.01H:ECX.PDCM [bit 15] is set. Therefore, kvm should raise #GP > > whenever a guest tries to read this MSR and the guest's > > CPUID.01H:ECX.PDCM [bit 15] is clear. > > > > Probably one more check would be better: > > if (!boot_cpu_has(X86_FEATURE_PDCM) || > !guest_cpuid_has(vcpu, X86_FEATURE_PDCM)) > return 1; Thanks for that change! > (host isn't expected to read this MSR when PDCM is not supported > by the guest, so don't have "!msr_info->host_initiate" added to above) In keeping with commit 44883f01fe6ae ("KVM: x86: ensure all MSRs can always be KVM_GET/SET_MSR'd"), I think the host_initiated check should be added.