Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754490AbbBRTfW (ORCPT ); Wed, 18 Feb 2015 14:35:22 -0500 Received: from mail-we0-f170.google.com ([74.125.82.170]:45756 "EHLO mail-we0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753175AbbBRTfU (ORCPT ); Wed, 18 Feb 2015 14:35:20 -0500 MIME-Version: 1.0 In-Reply-To: <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> <20150218192704.GA8441@gmail.com> Date: Wed, 18 Feb 2015 11:35:19 -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: 4445 Lines: 100 On Wed, Feb 18, 2015 at 11:27 AM, Ingo Molnar wrote: > > * 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? Sounds good to me. -- 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/