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 S1751666AbdJ0HHp convert rfc822-to-8bit (ORCPT <rfc822;w@1wt.eu>);
        Fri, 27 Oct 2017 03:07:45 -0400
Received: from prv-mh.provo.novell.com ([137.65.248.74]:34464 "EHLO
        prv-mh.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1750790AbdJ0HHo (ORCPT
        <rfc822;groupwise-linux-kernel@vger.kernel.org:10:1>);
        Fri, 27 Oct 2017 03:07:44 -0400
Message-Id: <59F2F75D020000780018A7E6@prv-mh.provo.novell.com>
X-Mailer: Novell GroupWise Internet Agent 14.2.2 
Date: Fri, 27 Oct 2017 01:07:41 -0600
From: "Jan Beulich" <JBeulich@suse.com>
To: "Sander Eikelenboom" <linux@eikelenboom.it>
Cc: "LKP" <lkp@01.org>, "Craig Bergstrom" <craigb@google.com>,
        "Fengguang Wu" <fengguang.wu@intel.com>,
        "Ingo Molnar" <mingo@kernel.org>,
        "Linus Torvalds" <torvalds@linux-foundation.org>,
        <wfg@linux.intel.com>, "Xen-devel" <xen-devel@lists.xen.org>,
        "Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [Xen-devel] ce56a86e2a ("x86/mm: Limit mmap() of /dev/mem
 to valid physical addresses"): kernel BUG at
 arch/x86/mm/physaddr.c:79!
References: <20171024024439.u3ywfgvi67fe4mbg@wfg-t540p.sh.intel.com>
 <c5082661-99a4-1b11-c8a1-8b31e9ab8d95@oracle.com>
 <CAOJUGyfTM2J-P29yPhUx2A2SDjA0rv972SE0hmbMHonthMd_bQ@mail.gmail.com>
 <440615a7-6cc0-a607-ce7c-22a34b69e8fe@eikelenboom.it>
 <1d203c07-0595-a33a-620b-c51eea9721d1@eikelenboom.it>
 <8721eeac-a644-e815-55e9-5f01956dd22a@eikelenboom.it>
 <CAOJUGye8nXL-J9oArLLMFz-RPRdKFe6EgqtYPSr5kcWoH2EodQ@mail.gmail.com>
 <20171026163911.dnovh4zaik5qumtt@gmail.com>
 <CAOJUGycO494NcvJk89MMub9Tbrj6FUoSNN4SOci7NgJRKq7v=A@mail.gmail.com>
 <207b6a75-2eff-8e92-d50c-ec2022fddbf9@eikelenboom.it>
In-Reply-To: <207b6a75-2eff-8e92-d50c-ec2022fddbf9@eikelenboom.it>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 8BIT
Content-Disposition: inline
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

>>> On 26.10.17 at 21:29, <linux@eikelenboom.it> wrote:
> On 26/10/17 19:49, Craig Bergstrom wrote:
>> Sander, thanks for the details, they've been very useful.
>> 
>> I suspect that your host system's mem=2048M parameter is causing the
>> problem.  Any chance you can confirm by removing the parameter and
>> running the guest code path?
> 
> I removed it, but kept the hypervisor limiting dom0 memory to 2046M intact 
> (in grub using the xen bootcmd: 
> "multiboot       /xen-4.10.gz  dom0_mem=2048M,max:2048M ....."
> 
> Unfortunately that doesn't change anything, the guest still fails to start 
> with the same errors.
> 
>> More specifically, since you're telling the kernel that it's high
>> memory address is at 2048M and your device is at 0xfe1fe000 (~4G), the
>> new mmap() limits are preventing you from mapping addresses that are
>> explicitly disallowed by the parameter.
>> 
> 
> Which would probably mean the current patch prohibits hard limiting the dom0 
> memory to a certain value (below 4G)
> at least in combination with PCI-passthrough. So the only thing left would 
> be to have no hard memory restriction on dom0
> and rely on auto-ballooning, but I'm not a great fan of that.

Plus - how would things work with any RAM size if the PCI BAR was
a 64-bit one, pointing somewhere high up beyond 4Gb?

Jan