From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751716AbdHAHrE (ORCPT <rfc822;w@1wt.eu>);
        Tue, 1 Aug 2017 03:47:04 -0400
Received: from mx2.suse.de ([195.135.220.15]:42342 "EHLO mx1.suse.de"
        rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP
        id S1751102AbdHAHrC (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 1 Aug 2017 03:47:02 -0400
Subject: Re: [PATCHv2 08/10] x86/mm: Replace compile-time checks for 5-level
 with runtime-time
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>, x86@kernel.org,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Andi Kleen <ak@linux.intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <20170718141517.52202-1-kirill.shutemov@linux.intel.com>
 <20170718141517.52202-9-kirill.shutemov@linux.intel.com>
 <6841c4f3-6794-f0ac-9af9-0ceb56e49653@suse.com>
 <20170725090538.26sbgb4npkztsqj3@black.fi.intel.com>
 <39cb1e36-f94e-32ea-c94a-2daddcbf3408@suse.com>
 <20170726164335.xaajz5ltzhncju26@node.shutemov.name>
From: Juergen Gross <jgross@suse.com>
Message-ID: <c450949e-bd79-c9c9-797e-be6b2c7b1e5f@suse.com>
Date: Tue, 1 Aug 2017 09:46:56 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.2.1
MIME-Version: 1.0
In-Reply-To: <20170726164335.xaajz5ltzhncju26@node.shutemov.name>
Content-Type: text/plain; charset=utf-8
Content-Language: de-DE
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

On 26/07/17 18:43, Kirill A. Shutemov wrote:
> On Wed, Jul 26, 2017 at 09:28:16AM +0200, Juergen Gross wrote:
>> On 25/07/17 11:05, Kirill A. Shutemov wrote:
>>> On Tue, Jul 18, 2017 at 04:24:06PM +0200, Juergen Gross wrote:
>>>> Xen PV guests will never run with 5-level-paging enabled. So I guess you
>>>> can drop the complete if (IS_ENABLED(CONFIG_X86_5LEVEL)) {} block.
>>>
>>> There is more code to drop from mmu_pv.c.
>>>
>>> But while there, I thought if with boot-time 5-level paging switching we
>>> can allow kernel to compile with XEN_PV and XEN_PVH, so the kernel image
>>> can be used in these XEN modes with 4-level paging.
>>>
>>> Could you check if with the patch below we can boot in XEN_PV and XEN_PVH
>>> modes?
>>
>> We can't. I have used your branch:
>>
>> git://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git
>> la57/boot-switching/v2
>>
>> with this patch applied on top.
>>
>> Doesn't boot PV guest with X86_5LEVEL configured (very early crash).
> 
> Hm. Okay.
> 
> Have you tried PVH?
> 
>> Doesn't build with X86_5LEVEL not configured:
>>
>>   AS      arch/x86/kernel/head_64.o
> 
> I've fixed the patch and split the patch into two parts: cleanup and
> re-enabling XEN_PV and XEN_PVH for X86_5LEVEL.
> 
> There's chance that I screw somthing up in clenaup part. Could you check
> that?

Build is working with and without X86_5LEVEL configured.

PV domU boots without X86_5LEVEL configured.

PV domU crashes with X86_5LEVEL configured:

xen_start_kernel()
  x86_64_start_reservations()
    start_kernel()
      setup_arch()
        early_ioremap_init()
          early_ioremap_pmd()

In early_ioremap_pmd() there seems to be a call to p4d_val() which is an
uninitialized paravirt operation in the Xen pv case.


HTH, Juergen