Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756111AbbBRSoI (ORCPT ); Wed, 18 Feb 2015 13:44:08 -0500 Received: from mail-wg0-f41.google.com ([74.125.82.41]:34743 "EHLO mail-wg0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932329AbbBRSoD (ORCPT ); Wed, 18 Feb 2015 13:44:03 -0500 MIME-Version: 1.0 In-Reply-To: <20150218183049.GA7032@gmail.com> References: <54E1CF5B.9020905@plexistor.com> <20150216220302.GF3364@wil.cx> <54E2FEF2.8060701@plexistor.com> <20150218183049.GA7032@gmail.com> Date: Wed, 18 Feb 2015 10:44:01 -0800 Message-ID: Subject: Re: [Linux-nvdimm] [PATCH 0/2] e820: Fix handling of NvDIMM chips From: Dan Williams To: Ingo Molnar 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" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2910 Lines: 64 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. > 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? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/