From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-wi0-x244.google.com ([2a00:1450:400c:c05::244]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1ZmMW5-00023b-Fp for kexec@lists.infradead.org; Wed, 14 Oct 2015 13:54:54 +0000 Received: by wicuv6 with SMTP id uv6so9579102wic.2 for ; Wed, 14 Oct 2015 06:54:31 -0700 (PDT) Date: Wed, 14 Oct 2015 15:54:28 +0200 From: Ingo Molnar Subject: Re: [V4 PATCH 4/4] x86/apic: Introduce noextnmi boot option Message-ID: <20151014135428.GC10316@gmail.com> References: <20151001062733.GL2881@worktop.programming.kicks-ass.net> <04EAB7311EE43145B2D3536183D1A8445499D30D@GSjpTKYDCembx31.service.hitachi.net> <20151001084335.GA3764@pd.tnic> <04EAB7311EE43145B2D3536183D1A8445499DB92@GSjpTKYDCembx31.service.hitachi.net> <20151001110110.GA3544@pd.tnic> <04EAB7311EE43145B2D3536183D1A8445499ED83@GSjpTKYDCembx31.service.hitachi.net> <20151002074721.GA16538@pd.tnic> <04EAB7311EE43145B2D3536183D1A844549A4557@GSjpTKYDCembx31.service.hitachi.net> <20151005082704.GA23259@nazgul.tnic> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Thomas Gleixner Cc: "x86@kernel.org" , Jonathan Corbet , 'Peter Zijlstra' , "linux-doc@vger.kernel.org" , "kexec@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Michal Hocko , =?utf-8?B?5bmz5p2+6ZuF5bezIC8gSElSQU1BVFXvvIxNQVNBTUk=?= , Ingo Molnar , Borislav Petkov , "Eric W. Biederman" , "H. Peter Anvin" , =?utf-8?B?5rKz5ZCI6Iux5a6PIC8gS0FXQUnvvIxISURFSElSTw==?= , Andrew Morton , Vivek Goyal CiogVGhvbWFzIEdsZWl4bmVyIDx0Z2x4QGxpbnV0cm9uaXguZGU+IHdyb3RlOgoKPiBCb3Jpc2xh diwKPiAKPiBPbiBNb24sIDUgT2N0IDIwMTUsIEJvcmlzbGF2IFBldGtvdiB3cm90ZToKPiA+IE9u IE1vbiwgT2N0IDA1LCAyMDE1IGF0IDAyOjAzOjU4QU0gKzAwMDAsIOays+WQiOiLseWujyAvIEtB V0FJ77yMSElERUhJUk8gd3JvdGU6Cj4gPiA+IFRoYXQncyBkaWZmZXJlbnQgZnJvbSBteSBwb2lu dCBvZiB2aWV3LiAgSSdtIG5vdCBnb2luZyB0byBwYXNzCj4gPiA+IHNvbWUgZGF0YSBmcm9tIHRo ZSBmaXJzdCBrZXJuZWwgdG8gdGhlIHNlY29uZCBrZXJuZWwuIEknbSBqdXN0IGdvaW5nIHRvCj4g PiA+IHByb3ZpZGUgYSBjb25maWd1cmFibGUgb3B0aW9uIGZvciB0aGUgc2Vjb25kIGtlcm5lbCB0 byB1c2Vycy4KPiA+IAo+ID4gRHVkZSwgV1RGPyEgWW91J3JlIGFkZGluZyBhIGtlcm5lbCBjb21t YW5kIGxpbmUgd2hpY2ggaXMgc3VwcG9zZWQgdG8KPiA+IGJlIHVzZWQgKm9ubHkqIGJ5IHRoZSBr ZHVtcCBrZXJuZWwuIEJ1dCBub29vLCBpdCBpcyB0aGVyZSBpbiB0aGUgb3Blbgo+ID4gYW5kIHZp c2libGUgdG8gcGVvcGxlLiBBbmQgYW55b25lIGNhbiB0eXBlIGl0IGluIGR1cmluZyBib290LiBB 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1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753974AbbJNNyf (ORCPT ); Wed, 14 Oct 2015 09:54:35 -0400 Received: from mail-wi0-f196.google.com ([209.85.212.196]:33176 "EHLO mail-wi0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753579AbbJNNyd (ORCPT ); Wed, 14 Oct 2015 09:54:33 -0400 Date: Wed, 14 Oct 2015 15:54:28 +0200 From: Ingo Molnar To: Thomas Gleixner Cc: Borislav Petkov , =?utf-8?B?5rKz5ZCI6Iux5a6PIC8gS0FXQUnvvIxISURFSElSTw==?= , "'Peter Zijlstra'" , Jonathan Corbet , "Eric W. Biederman" , "H. Peter Anvin" , Andrew Morton , Vivek Goyal , "linux-doc@vger.kernel.org" , "x86@kernel.org" , "kexec@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Michal Hocko , Ingo Molnar , =?utf-8?B?5bmz5p2+6ZuF5bezIC8gSElSQU1BVFXvvIxNQVNBTUk=?= Subject: Re: [V4 PATCH 4/4] x86/apic: Introduce noextnmi boot option Message-ID: <20151014135428.GC10316@gmail.com> References: <20151001062733.GL2881@worktop.programming.kicks-ass.net> <04EAB7311EE43145B2D3536183D1A8445499D30D@GSjpTKYDCembx31.service.hitachi.net> <20151001084335.GA3764@pd.tnic> <04EAB7311EE43145B2D3536183D1A8445499DB92@GSjpTKYDCembx31.service.hitachi.net> <20151001110110.GA3544@pd.tnic> <04EAB7311EE43145B2D3536183D1A8445499ED83@GSjpTKYDCembx31.service.hitachi.net> <20151002074721.GA16538@pd.tnic> <04EAB7311EE43145B2D3536183D1A844549A4557@GSjpTKYDCembx31.service.hitachi.net> <20151005082704.GA23259@nazgul.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit 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 * Thomas Gleixner wrote: > Borislav, > > On Mon, 5 Oct 2015, Borislav Petkov wrote: > > On Mon, Oct 05, 2015 at 02:03:58AM +0000, 河合英宏 / KAWAI，HIDEHIRO wrote: > > > That's different from my point of view. I'm not going to pass > > > some data from the first kernel to the second kernel. I'm just going to > > > provide a configurable option for the second kernel to users. > > > > Dude, WTF?! You're adding a kernel command line which is supposed to > > be used *only* by the kdump kernel. But nooo, it is there in the open > > and visible to people. And anyone can type it in during boot. AND THAT > > SHOULDN'T BE POSSIBLE IN THE FIRST PLACE! > > > > This information is strictly for the kdump kernel - it shouldn't be a > > generic command line option. How hard it is to understand that simple > > fact?! > > Calm down! > > Disabling that NMI in the first kernel is not going to make the world > explode. We have enough command line options a user can type in, which > are way worse than that one. If some "expert" types nonsense on the > first kernel command line, then it's none of our problems, really. > > If Kawai would have marked that option as a debug feature, this > discussion would have probably never happened. > > Aside of that, the best way to hand in options for the kdump kernel is > the command line. We have an existing interface for that. > > Let's move on. Nothing to see here. So Boris kind of has a point: there are numerous problems with boot options as kexec parameter interface: - boot option strings are not a well defined programmatic interface: - failures are not obvious (they are often ignored) - inserting/setting parameters is awkward as well. - boot options are not an ABI, so when options have dual use with kexec it's easy to break things inadvertently: without that failure being apparent other than reintroducing obscure kexec failure modes again. - in the booted up kexec kernel it's not really obvious which options got set by kexec and which got set by the user - as there's no separation of namespaces. - likewise, if the user specifies an option in conflict with a kexec requirement it's not really obvious what's happening: the user setting should probably dominate - I'm not sure that's the case with the current kexec code. Boot options are basically a user interface. On the other hand the hack of (ab-)using boot parameters as kexec parameter passing is an existing, many years old practice and we cannot just stop it without offering an alternative (and better!) interface first. We could improve things by either adding a separate kexec-only parameter passing facility (like programmatic boot parameters are) - or by creating some sort of boot parameter alias that clearly identifies kexec parameters. So for example when introducing 'noextnmi' we'd also add a facility to add a 'kexec_noextnmi' alias - which clearly identifies this boot parameter as a kexec related one. Every 'kexec' inserted parameter would be prefixed by kexec_ - and then the separation of namespaces (and the prioritization of user vs. kexec requirements) becomes well defined as well.. We should also probably print a warning if a kexec_* parameter is passed in that has no matching handler in the kexec()-ed kernel. I do concur that this patch is probably OK given existing practices. Thanks, Ingo