From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753483AbbBRSxe (ORCPT ); Wed, 18 Feb 2015 13:53:34 -0500 Received: from mail-wg0-f43.google.com ([74.125.82.43]:58343 "EHLO mail-wg0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752000AbbBRSxc (ORCPT ); Wed, 18 Feb 2015 13:53:32 -0500 Date: Wed, 18 Feb 2015 19:53:27 +0100 From: Ingo Molnar To: Dan Williams Cc: Boaz Harrosh , Matthew Wilcox , Ingo Molnar , Ross Zwisler , x86@kernel.org, linux-kernel , "Roger C. Pao" , Thomas Gleixner , Linus Torvalds , linux-nvdimm , "H. Peter Anvin" Subject: Re: [Linux-nvdimm] [PATCH 0/2] e820: Fix handling of NvDIMM chips Message-ID: <20150218185327.GA7828@gmail.com> References: <54E1CF5B.9020905@plexistor.com> <20150216220302.GF3364@wil.cx> <54E2FEF2.8060701@plexistor.com> <20150218183049.GA7032@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Dan Williams wrote: > On Wed, Feb 18, 2015 at 10:30 AM, Ingo Molnar wrote: > > > > * Dan Williams wrote: > > > >> On Tue, Feb 17, 2015 at 12:42 AM, Boaz Harrosh wrote: > >> > On 02/17/2015 12:03 AM, Matthew Wilcox wrote: > >> >> On Mon, Feb 16, 2015 at 01:07:07PM +0200, Boaz Harrosh wrote: > >> >>> In any way this is a problem for the new type-12 NvDIMM memory chips that > >> >>> are circulating around. (It is estimated that there are already 100ds of > >> >>> thousands NvDIMM chips in active use) > >> >> > >> >> Hang on. NV-DIMM chips don't know anyhing about E820 > >> >> tables. They don't have anything in them that says "I > >> >> am type 12!". How they are reported is up to the > >> >> BIOS. Just because your BIOS vendor has chosen to > >> >> report tham as type 12 doesn't mean that any other > >> >> BIOS vedor is going to have done the same thing. > >> >> > >> >> Fortunately, the BIOS people have all got together and > >> >> decided what they're going to do, and it's not type > >> >> 12. Unfortunately, I think I'm bound by various > >> >> agreements to not say what they are going to do until > >> >> they do. But putting this temporary workaround in the > >> >> kernel to accomodate one BIOS vendor's unreleased > >> >> experimental code seems like entirely the wrong idea. > >> >> > >> > > >> > I had a feeling I'm entering an holy war ;-). > >> > > >> > I hope you are OK with my first patch. That an unknown > >> > type need not be reported busy, and behave same as > >> > "reserved"? > >> > >> No, it seems the safe thing to do is prevent the > >> kernel from accessing any memory that it does not know > >> the side-effects of accessing. > > > > Well, except when the kernel does know how to access > > it: when an nvdimm driver knows about its own memory > > region and knows how to handle it, right? > > Yes, except that "type-12" is something picked out of the > air that may be invalidated by a future spec change. > > If firmware wants any driver to handle a memory range it > can already use E820_RESERVED. The only reason a > new-type was picked in these early implementations was > for experiments around reserving nvdimm memory for driver > use, but also extending it to be covered with struct page > mappings. Outside of that there is no real driving > reason for the new type. But ... if a user is blessed/haunted with such firmware, why not let new types fall back to 'reserved', which is a reasonable default that still allows sufficiently aware Linux drivers to work, right? > > So is there any practical reason to mark the memory > > resource as busy in that case, instead of just adding > > it to the reserved list by default and allowing > > properly informed drivers to (exclusively) request it? > > I'm not sure we want firmware to repeat this confusion > going forward. Why support new memory types unless > defined by ACPI or otherwise sufficiently described by > E820_RESERVED? Because it would make the kernel more functional? We should always err on the side of allowing more functionality and not erect roadblocks. Thanks, Ingo