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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 5A245C07E9E for ; Mon, 12 Jul 2021 09:39:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4414F60FE9 for ; Mon, 12 Jul 2021 09:39:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237660AbhGLJmg (ORCPT ); Mon, 12 Jul 2021 05:42:36 -0400 Received: from mga17.intel.com ([192.55.52.151]:12193 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237631AbhGLJjU (ORCPT ); Mon, 12 Jul 2021 05:39:20 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10042"; a="190332116" X-IronPort-AV: E=Sophos;i="5.84,232,1620716400"; d="scan'208";a="190332116" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Jul 2021 02:36:32 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.84,232,1620716400"; d="scan'208";a="491957343" Received: from michael-optiplex-9020.sh.intel.com (HELO localhost) ([10.239.159.182]) by FMSMGA003.fm.intel.com with ESMTP; 12 Jul 2021 02:36:30 -0700 Date: Mon, 12 Jul 2021 17:50:34 +0800 From: Yang Weijiang To: Jim Mattson Cc: Yang Weijiang , pbonzini@redhat.com, seanjc@google.com, vkuznets@redhat.com, wei.w.wang@intel.com, like.xu.linux@gmail.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 06/13] KVM: x86/vmx: Save/Restore host MSR_ARCH_LBR_CTL state Message-ID: <20210712095034.GD12162@intel.com> References: <1625825111-6604-1-git-send-email-weijiang.yang@intel.com> <1625825111-6604-7-git-send-email-weijiang.yang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 09, 2021 at 03:54:53PM -0700, Jim Mattson wrote: > On Fri, Jul 9, 2021 at 2:51 AM Yang Weijiang wrote: > > > > If host is using MSR_ARCH_LBR_CTL then save it before vm-entry > > and reload it after vm-exit. > > I don't see anything being done here "before VM-entry" or "after > VM-exit." This code seems to be invoked on vcpu_load and vcpu_put. > > In any case, I don't see why this one MSR is special. It seems that if > the host is using the architectural LBR MSRs, then *all* of the host > architectural LBR MSRs have to be saved on vcpu_load and restored on > vcpu_put. Shouldn't kvm_load_guest_fpu() and kvm_put_guest_fpu() do > that via the calls to kvm_save_current_fpu(vcpu->arch.user_fpu) and > restore_fpregs_from_fpstate(&vcpu->arch.user_fpu->state)? I looked back on the discussion thread: https://patchwork.kernel.org/project/kvm/patch/20210303135756.1546253-8-like.xu@linux.intel.com/ not sure why this code is added, but IMO, although fpu save/restore in outer loop covers this LBR MSR, but the operation points are far away from vm-entry/exit point, i.e., the guest MSR setting could leak to host side for a signicant long of time, it may cause host side profiling accuracy. if we save/restore it manually, it'll mitigate the issue signifcantly.