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 S1423552AbcBQSmr (ORCPT <rfc822;w@1wt.eu>);
	Wed, 17 Feb 2016 13:42:47 -0500
Received: from g4t3426.houston.hp.com ([15.201.208.54]:44428 "EHLO
	g4t3426.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1423388AbcBQSmj (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 17 Feb 2016 13:42:39 -0500
Message-ID: <1455737737.2925.280.camel@hpe.com>
Subject: Re: [PATCH] x86/mm: Add x86 valid_phys_addr_range() for /dev/mem
From: Toshi Kani <toshi.kani@hpe.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@suse.de>,
        "linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>,
        X86 ML <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Date: Wed, 17 Feb 2016 12:35:37 -0700
In-Reply-To: <CAPcyv4j_TS3BXv0SyJzNg_FDdEB9uOmzTtibkS-Z_jAv_PDZiA@mail.gmail.com>
References: <1455069975-14291-1-git-send-email-toshi.kani@hpe.com>
	 <CAPcyv4j_TS3BXv0SyJzNg_FDdEB9uOmzTtibkS-Z_jAv_PDZiA@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.18.4 (3.18.4-1.fc23) 
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, 2016-02-17 at 09:58 -0800, Dan Williams wrote:
> On Tue, Feb 9, 2016 at 6:06 PM, Toshi Kani <toshi.kani@hpe.com> wrote:
> > x86 does not define ARCH_HAS_VALID_PHYS_ADDR_RANGE, which
> > leads /dev/mem to use the default valid_phys_addr_range()
> > and valid_mmap_phys_addr_range() in drivers/char/mem.c.
> > 
> > The default valid_phys_addr_range() allows any range lower
> > than __pa(high_memory), which is the end of system RAM, and
> > disallows any range higher than it.
> > 
> > Persistent memory may be located at lower and/or higher
> > address of __pa(high_memory) depending on their memory slots.
> > When using crash(8) via /dev/mem for analyzing data in
> > persistent memory, it can only access to the one lower than
> > __pa(high_memory).
> > 
> > Add x86 valid_phys_addr_range() and valid_mmap_phys_addr_range()
> > to provide better checking:
> >  - Physical address range is valid when it is fully backed by
> >    IORESOURCE_MEM, regardless of __pa(high_memory).
> >  - Other ranges, including holes, are invalid.
> > 
> > This also allows crash(8) to access persistent memory ranges
> > via /dev/mem (with a minor change to remove high_memory check
> > from crash itself).
> 
> If we're modifying crash(8) can't we also teach it to mmap /dev/pmemX
> directly?  With commit 90a545e98126 "restrict /dev/mem to idle io
> memory ranges" /dev/mem should not have access to active pmem ranges.

Yes, I am aware of the commit.  Unloading drivers while using crash(8) to
analyze NVDIMM via /dev/mem makes sense.  /dev/mem does not require any
other drivers be loaded.

Using /dev/pmemX, on the other hand, requires the driver to be loaded,
which can be problematic.  For instance, when btt_init() fails due to some
corruption in arena, it fails to create any pmem device file.  A dev file
also restricts access range within the dev file.

Thanks,
-Toshi

ps.
Looking at iomem_is_exclusive(), it only checks the top-level iomem
entries.  I think the pmem/btt driver only marks a child entry busy...