From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@kernel.org>
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 B063DC433F5
	for <linux-kernel@archiver.kernel.org>; Wed, 16 Feb 2022 18:03:04 +0000 (UTC)
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S237412AbiBPSDP (ORCPT <rfc822;linux-kernel@archiver.kernel.org>);
        Wed, 16 Feb 2022 13:03:15 -0500
Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:54272 "EHLO
        lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S237402AbiBPSDN (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 16 Feb 2022 13:03:13 -0500
Received: from mail.skyhub.de (mail.skyhub.de [5.9.137.197])
        by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2B6A2293B62
        for <linux-kernel@vger.kernel.org>; Wed, 16 Feb 2022 10:03:00 -0800 (PST)
Received: from zn.tnic (dslb-088-067-221-104.088.067.pools.vodafone-ip.de [88.67.221.104])
        (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
        (No client certificate requested)
        by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 75C7F1EC0518;
        Wed, 16 Feb 2022 19:02:55 +0100 (CET)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim;
        t=1645034575;
        h=from:from:reply-to:subject:subject:date:date:message-id:message-id:
         to:to:cc:cc:mime-version:mime-version:content-type:content-type:
         content-transfer-encoding:in-reply-to:in-reply-to:  references:references;
        bh=jBtlGm8WJFBOdlSzBUlWwC0q4z+PZ1kReU2GS1VtCzg=;
        b=jbE12Yg54ODKlG6g3sf+XPrMSH70l35ZbFTc1OevwaYL0I99jU3mxv888vgnbJJsai/bLf
        /XYD0BnZJ2Ch332IwqA7PoBGo4OLSA3J0xwWvzqs9ZDP7B//X5TGWpwSAzz1VRYruNuEEp
        Wi3EUUglWkMOh4wqFo4hZTm5iVjJg1g=
Date:   Wed, 16 Feb 2022 19:02:58 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Jue Wang <juew@google.com>
Cc:     "Luck, Tony" <tony.luck@intel.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, patches@lists.linux.dev
Subject: Re: [PATCH] x86/mce: Add workaround for SKX/CLX/CPX spurious machine
 checks
Message-ID: <Yg08Uhg0fZ9xZuP2@zn.tnic>
References: <CAPcxDJ7nriZEJHF6dMPR7tQ+dGuueyRjw1NC+4CbjxiAT_S+ZA@mail.gmail.com>
 <20220208150945.266978-1-juew@google.com>
 <Ygwka++3eipjQzB2@zn.tnic>
 <YgwnqTc8FGG3orcE@agluck-desk3.sc.intel.com>
 <YgzRsfWOmqkNiNI7@zn.tnic>
 <CAPcxDJ4=iknzYbN=b2oQxvJyODkQ_MWEj1wkKEuGwf4HQ3aPZA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CAPcxDJ4=iknzYbN=b2oQxvJyODkQ_MWEj1wkKEuGwf4HQ3aPZA@mail.gmail.com>
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Feb 16, 2022 at 07:50:24AM -0800, Jue Wang wrote:
> My slight reservation is that this suggests all use cases of "REP;
> MOVS*" must take the _ASM_EXTABLE_ form, which is not possible;
> considering "REP; MOVS*" can be exercised from any user space program.

Well, we could try to decode the instructions around rIP when the #MC
is raised and see what caused the MCE and perhaps pick apart which insn
caused it, is it accessing behind the buffer boundaries, etc.

> If there is a way to get all users of "REP; MOVS*" to use
> copy_mc_enhanced_fast_string, this could work. I am not sure this is
> possible.

Yeah, no, this is for the copy to user direction only.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette