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 A0CC1C433F5 for ; Tue, 4 Oct 2022 21:07:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229619AbiJDVHw (ORCPT ); Tue, 4 Oct 2022 17:07:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33578 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229513AbiJDVHs (ORCPT ); Tue, 4 Oct 2022 17:07:48 -0400 Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 13EF66AE9D; Tue, 4 Oct 2022 14:07:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1664917668; x=1696453668; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=f+bN7q0J598sgXYDRSmOgQEwWqaQ4PKzdTfPJ/hdZRg=; b=n6C0xOU7NZCTX+r0iIhz4jEDEAo+EdjKN1SHJj9+1uv1LklASa3C32Qe E5caVZMKcnOavlvHy8OmMrZENZJDG8EJvJ0YDtjQQN0zRH2gNhSs6os3N CG6IXjq3QoZEN8OVIwXnuHwMwXki3hw9tvJh6kxe5WFpQ+cQifbCp9VJk mzuaY02QeJ96yZPP5dV2IscK12hkpKsetNGPDgB3kiqAygYVlnxhzS1/v fLSX2RUBJbVH8vqxfwe+ZHOx6wPc7R1XAELWYQEGrTLiQmf78NV8BevAv MZU8TUz9+/BIm2+FRuveXV86dfnSe+tcBEJ18WVH8zCEtxM+vtkj7NT/N Q==; X-IronPort-AV: E=McAfee;i="6500,9779,10490"; a="300626789" X-IronPort-AV: E=Sophos;i="5.95,158,1661842800"; d="scan'208";a="300626789" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Oct 2022 14:07:47 -0700 X-IronPort-AV: E=McAfee;i="6500,9779,10490"; a="869174199" X-IronPort-AV: E=Sophos;i="5.95,158,1661842800"; d="scan'208";a="869174199" Received: from samrober-mobl.amr.corp.intel.com (HELO [10.209.85.136]) ([10.209.85.136]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Oct 2022 14:07:46 -0700 Message-ID: Date: Tue, 4 Oct 2022 14:07:45 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: Finish removing MPX from arch/x86? Content-Language: en-US To: Jim Mattson Cc: Sean Christopherson , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Arjan van de Ven References: <547a1203-0339-7ad2-9505-eab027046298@intel.com> From: Dave Hansen In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/4/22 11:21, Jim Mattson wrote: > On Tue, Oct 4, 2022 at 10:45 AM Dave Hansen wrote: >> >> We zapped the userspace MPX ABIs and most of its supporting code in here: >> >> 45fc24e89b7c ("x86/mpx: remove MPX from arch/x86") >> >> But, the XSAVE enabling and KVM code were left in place. This let folks >> at least keep running guests with MPX. >> >> It's been a couple of years and I don't think I've had a single person >> opine about the loss of MPX. Intel also followed through and there's no >> MPX to be found on newer CPUs like my "Tiger Lake" 11th Gen Intel(R) >> Core(TM) i7-1165G7. >> >> Is it time to zap MPX from arch/x86/kvm/? > > Until Google Cloud retires all of our MPX-capable hardware, we will > require MPX support in KVM. > > Removing that support would leave VMs with MPX enabled in XCR0 with > nowhere to go. Is this because you migrate guest VMs between hosts? A _potential_ VM migration target host is ineligible if it has a subset of the features of the source host? Would it be _possible_ to leave existing VMs alone, but to stop enumerating MPX to newly-created VMs? I don't know how long-lived your VMs are, but I'm hoping that the ones that know about MPX will all die naturally of old age at some point.