Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S934798AbeAKPv5 (ORCPT <rfc822;ralf@linux-mips.org> + 1 other);
        Thu, 11 Jan 2018 10:51:57 -0500
Received: from mga07.intel.com ([134.134.136.100]:45506 "EHLO mga07.intel.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S932223AbeAKPv4 (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 11 Jan 2018 10:51:56 -0500
X-Amp-Result: SKIPPED(no attachment in message)
X-Amp-File-Uploaded: False
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.46,345,1511856000"; 
   d="scan'208";a="10479998"
Subject: Re: [RFC PATCH v2 6/6] x86/entry/pti: don't switch PGD on when
 pti_disable is set
To: Willy Tarreau <w@1wt.eu>
References: <1515502580-12261-1-git-send-email-w@1wt.eu>
 <1515502580-12261-7-git-send-email-w@1wt.eu>
 <20180110082207.GX29822@worktop.programming.kicks-ass.net>
 <20180110091102.GH14066@1wt.eu>
 <CALCETrXQFL2sJPJe_Z8XLEo11V_tLyZR0y4PTRxJzrhmpdsuJg@mail.gmail.com>
 <CA+55aFwfSKNAYEFWCwCe2vSxejA3X85FnX9t1EdnCRUwC1ou1Q@mail.gmail.com>
 <20180111064259.GC14920@1wt.eu>
 <0f08d89e-61e1-20e3-5c59-0b2f7b32bf0c@linux.intel.com>
 <20180111154412.GA15296@1wt.eu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Brian Gerst <brgerst@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kees Cook <keescook@chromium.org>
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <af80ba81-f8bc-156e-a286-0825aa47f134@linux.intel.com>
Date: Thu, 11 Jan 2018 07:51:45 -0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.5.0
MIME-Version: 1.0
In-Reply-To: <20180111154412.GA15296@1wt.eu>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Return-Path: <linux-kernel-owner@vger.kernel.org>

On 01/11/2018 07:44 AM, Willy Tarreau wrote:
>> I think we also need to be able to dump the actual
>> CR3 value that we entered the kernel with before we start doing too much
>> other funky stuff with the entry code.
> When you say dump, you mean save it somewhere in a per_cpu variable ?

Yeah, I think a per-cpu variable is fine for now.  But, that only gives
you a dump from a single entry to the kernel.  Ideally, it would be nice
to have a stack of them so you could do things like debug
syscall->fault->oops.  Was it the syscall entry or the fault entry that
lead to the oops?

But, the stack gets really fun because of NMIs.

I'm sure Andy Lutomirski has some ideas too.