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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 BB1ADC433E0 for ; Tue, 23 Feb 2021 03:08:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8AB2E64DEC for ; Tue, 23 Feb 2021 03:08:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231287AbhBWDIM (ORCPT ); Mon, 22 Feb 2021 22:08:12 -0500 Received: from mga18.intel.com ([134.134.136.126]:39519 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230371AbhBWDIG (ORCPT ); Mon, 22 Feb 2021 22:08:06 -0500 IronPort-SDR: I8wXa8ArozbdbxPwY53kk5faNHIMnlQrp+QCWQlkM0D78onUvC1p8l3h/a6rnRWCSvriJcCtGM NiAqvaiBEibw== X-IronPort-AV: E=McAfee;i="6000,8403,9903"; a="172328668" X-IronPort-AV: E=Sophos;i="5.81,199,1610438400"; d="scan'208";a="172328668" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Feb 2021 19:06:20 -0800 IronPort-SDR: /6nIHWVZ2rpqTZY1ehs80a1kmL2cWW/xE31i8LO+JI9Cxx8taUxDi58kqjnss8+AUxM1dUD9GM PXRmw2W6g5eQ== X-IronPort-AV: E=Sophos;i="5.81,199,1610438400"; d="scan'208";a="402919857" Received: from unknown (HELO [10.238.130.200]) ([10.238.130.200]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Feb 2021 19:06:16 -0800 Subject: Re: [PATCH v1] kvm: x86: Revise guest_fpu xcomp_bv field To: Sean Christopherson Cc: Dave Hansen , pbonzini@redhat.com, Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210208161659.63020-1-jing2.liu@linux.intel.com> <4e4b37d1-e2f8-6757-003c-d19ae8184088@intel.com> From: "Liu, Jing2" Message-ID: <9d23ae5b-9b85-88d7-a2d7-44fd75a068b9@linux.intel.com> Date: Tue, 23 Feb 2021 11:06:14 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/23/2021 12:06 AM, Sean Christopherson wrote: > On Mon, Feb 22, 2021, Liu, Jing2 wrote: >> On 2/9/2021 1:24 AM, Sean Christopherson wrote: >>> On Mon, Feb 08, 2021, Dave Hansen wrote: >>>> On 2/8/21 8:16 AM, Jing Liu wrote: >>>>> -#define XSTATE_COMPACTION_ENABLED (1ULL << 63) >>>>> - >>>>> static void fill_xsave(u8 *dest, struct kvm_vcpu *vcpu) >>>>> { >>>>> struct xregs_state *xsave = &vcpu->arch.guest_fpu->state.xsave; >>>>> @@ -4494,7 +4492,8 @@ static void load_xsave(struct kvm_vcpu *vcpu, u8 *src) >>>>> /* Set XSTATE_BV and possibly XCOMP_BV. */ >>>>> xsave->header.xfeatures = xstate_bv; >>>>> if (boot_cpu_has(X86_FEATURE_XSAVES)) >>>>> - xsave->header.xcomp_bv = host_xcr0 | XSTATE_COMPACTION_ENABLED; >>>>> + xsave->header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT | >>>>> + xfeatures_mask_all; >>> This is wrong, xfeatures_mask_all also tracks supervisor states. >> When looking at SDM Vol2 XSAVES instruction Operation part, it says as >> follows, >> >> RFBM ← (XCR0 OR IA32_XSS) AND EDX:EAX; >> COMPMASK ← RFBM OR 80000000_00000000H; >> ... >> >> XCOMP_BV field in XSAVE header ← COMPMASK; >> >> >> So it seems xcomp_bv also tracks supervisor states? > Yes, sorry, I got distracted by Dave's question and didn't read the changelog > closely. > > Now that I have, I find "Since fpstate_init() has initialized xcomp_bv, let's > just use that." confusing. I think what you intend to say is that we can use > the same _logic_ as fpstate_init_xstate() for calculating xcomp_bv. Yes, that's the idea. > > That said, it would be helpful for the changelog to explain why it's correct to > use xfeatures_mask_all, e.g. just a short comment stating that the variable holds > all XCR0 and XSS bits enabled by the host kernel. Justifying a change with > "because other code does it" is sketchy, becuse there's no guarantee that what > something else does is also correct for KVM, or that the existing code itself is > even correct. Got it, thanks for the details on this. Then how about making the commit message like, XCOMP_BV[63] field indicates that the save area is in the compacted format and XCOMP_BV[62:0] indicates the states that have space allocated in the save area, including both XCR0 and XSS bits enable by the host kernel. Use xfeatures_mask_all for calculating xcomp_bv and reuse XCOMP_BV_COMPACTED_FORMAT defined by kernel. Thanks, Jing