From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754945AbbBRT1M (ORCPT ); Wed, 18 Feb 2015 14:27:12 -0500 Received: from mail-we0-f177.google.com ([74.125.82.177]:33307 "EHLO mail-we0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753459AbbBRT1J (ORCPT ); Wed, 18 Feb 2015 14:27:09 -0500 Date: Wed, 18 Feb 2015 20:27:04 +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: <20150218192704.GA8441@gmail.com> References: <54E1CF5B.9020905@plexistor.com> <20150216220302.GF3364@wil.cx> <54E2FEF2.8060701@plexistor.com> <20150218183049.GA7032@gmail.com> <20150218185327.GA7828@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 10:53 AM, Ingo Molnar wrote: > > > > * 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? > > True. > > > > >> > 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. > > > > I'm not convinced Linux is better off enabling one-off > BIOS implementations to pick non-standard numbers. Would > it not be safer to at least confirm with the user via a > configuration option, "do you want drivers to access > unknown memory types"? Well, we could emit a warning (or taint the kernel), to keep the user informed that there's a version mismatch between kernel and firmware - but otherwise still allow informed drivers to register that region? Thanks, Ingo