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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9880CE9271E for ; Thu, 5 Oct 2023 17:52:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231246AbjJERwd (ORCPT ); Thu, 5 Oct 2023 13:52:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53024 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229777AbjJERw3 (ORCPT ); Thu, 5 Oct 2023 13:52:29 -0400 Received: from mgamail.intel.com (mgamail.intel.com [134.134.136.126]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 58014A6; Thu, 5 Oct 2023 10:52:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1696528348; x=1728064348; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=TtiSPYzoUtvmt+GaR6E65uzRaBQ5yy2BuLcs6NWBp9E=; b=DxXg2s2XE4921TLu0BvxDtuf5w8psxB+7mJwoitOz/sAw7zwfOEAsnCH DtGISsniO9N7eG4ornDYlyCZTkfkaoAbcGL6ijFDKwUu1SoOSEdeG261j 67WFksSrUlVDEY1q64Nq4ZBWko90AqXMnnJEQCVFEyzvVtFFj7UbPFsiw vak5mNPBoYSxo/3kPuD5A8qmGC3RiI5Bl1GZirHPyeJ7cF6G9uXUXEEoY cyqEE7ADMaLH2rtHCGjJEiMHbIYYiU3okFQhiY9JDkWx9YomZUI/uB39S KOswtAi6uSi+YQCwl4BCjqJZsqXpykpoxS178+S8osaQE/b4s+w4qtHIT Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10854"; a="368648041" X-IronPort-AV: E=Sophos;i="6.03,203,1694761200"; d="scan'208";a="368648041" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Oct 2023 10:52:27 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10854"; a="701744560" X-IronPort-AV: E=Sophos;i="6.03,203,1694761200"; d="scan'208";a="701744560" Received: from emosbarx-mobl2.amr.corp.intel.com (HELO [10.209.23.184]) ([10.209.23.184]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Oct 2023 10:52:01 -0700 Message-ID: <4059e9c6-e85b-085f-b5c5-9da209bbfab2@intel.com> Date: Thu, 5 Oct 2023 10:52:01 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH] x86: KVM: Add feature flag for AMD's FsGsKernelGsBaseNonSerializing Content-Language: en-US To: Jim Mattson Cc: Borislav Petkov , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Pawan Gupta , Jiaxi Chen , Kim Phillips , Paolo Bonzini , Sean Christopherson , "H. Peter Anvin" , x86@kernel.org, Dave Hansen , Ingo Molnar , Thomas Gleixner References: <20231004002038.907778-1-jmattson@google.com> <01009a2a-929e-ce16-6f44-1d314e6bcba5@intel.com> <20231004075836.GBZR0bLC/Y09sSSYWw@fat_crate.local> From: Dave Hansen In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 10/5/23 09:41, Jim Mattson wrote: >> >> But I'm struggling to think of cases where Intel has read-only >> "defeature bits" like this one. There are certainly things like >> MSR_IA32_MISC_ENABLE_FAST_STRING that can be toggled, but read-only >> indicators of a departure from established architecture seems ... >> suboptimal. ... > CPUID.(EAX=7,ECX=0):EBX[bit 13] (Haswell) - "Deprecates FPU CS and FPU > DS values if 1." > CPUID.(EAX=7,ECX=0):EBX[bit 6] (Skylake) - "FDP_EXCPTN_ONLY. x87 FPU > Data Pointer updated only on x87 exceptions if 1." Thanks! Trying to group these does make sense to me. I don't think people take architecture breakage lightly, but I certainly never considered that it might, for instance, be important enough to create a new VM migration pool. I'll try to keep an eye out for these.