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=-4.0 required=3.0 tests=BAYES_00,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 CE730C433B4 for ; Wed, 31 Mar 2021 22:12:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 978346108C for ; Wed, 31 Mar 2021 22:12:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230380AbhCaWMD (ORCPT ); Wed, 31 Mar 2021 18:12:03 -0400 Received: from mail-ed1-f43.google.com ([209.85.208.43]:45944 "EHLO mail-ed1-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229497AbhCaWLn (ORCPT ); Wed, 31 Mar 2021 18:11:43 -0400 Received: by mail-ed1-f43.google.com with SMTP id bx7so24039986edb.12; Wed, 31 Mar 2021 15:11:42 -0700 (PDT) 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=Y2axwWxTL8XPpHwUo4AVE1zruv6RF5CEAUfc387i7Es=; b=MUI0Rz04kwGUZSu+DD2JrZWSaRabmNc/h+GGyp1XexmOj+wEsIcAdM8A67S+1imDCS kiVK1AOWbMbd8SuUWhYz1SxwIqVKlQ/7ckQcYZhOMjIHuDX9bAjW+wxidKwnWAxLuJSB NkBXnRflmSUurzuUbBj2KicF/RqRU/pTZbpiRwlVGMa3w3lLozyMjAZqlKmicxrlQkde Pa4n8hU8XwbmDsspTSyLgTtg9xoDCF5jHjUGVWRydXprvtf78azBam8KHlPj9bdXfTB8 FKw1MI+VRr8mm1snJpYua2PtYd2R+SVdy/XCLCAnRD64425mZNlcvKmPJH/3rfHpdtWI S97Q== X-Gm-Message-State: AOAM532OOaE/8sWvLyBAXmoDcxDfvNo7lwWCP4yBRrxE71GU33epAl6y KzhsPMUOySEH8WxWbIQdPD8wTYZ42D2afpFRnug= X-Google-Smtp-Source: ABdhPJxF0AoPasiOPUQ+0kRTOZRzhmrm9mBUogAT7SW0kIY9/mhNKnb1B9vGVs2u4pcp4dvBgMyrOrOTNlzbCilvdZs= X-Received: by 2002:aa7:d917:: with SMTP id a23mr6430206edr.122.1617228702378; Wed, 31 Mar 2021 15:11:42 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Len Brown Date: Wed, 31 Mar 2021 18:11:31 -0400 Message-ID: Subject: Re: Candidate Linux ABI for Intel AMX and hypothetical new related features To: robert@ocallahan.org Cc: Andy Lutomirski , David Laight , Dave Hansen , Andy Lutomirski , Greg KH , "Bae, Chang Seok" , X86 ML , LKML , libc-alpha , Florian Weimer , Rich Felker , Kyle Huey , Keno Fischer , Linux API Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Wed, Mar 31, 2021 at 5:42 PM Robert O'Callahan wrote: > > For the record, the benefits of dynamic XCR0 for rr recording > portability still apply. I guess it'd be useful for CRIU too. We would > also benefit from anything that incentivizes increased support for > CPUID faulting. As previously mentioned, today we don't have an architectural way to trap a user into the kernel on CPUID, even though we can do this for a VMM. But spoofing CPUID isn't a solution to all problems. The feature really needs to be OFF to prevent users from using it, even if the supported mechanisms of discovering that feature say "NOT PRESENT". Today there are plenty of users who will opportunistically try everything in the cloud and choose the machine that allows them to do something that other machines will not -- even if it is not officially supported. If something is not enumerated, it really needs to also be turned off. cheers, --Len Brown, Intel Open Source Technology Center