From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755608Ab3A2J1H (ORCPT ); Tue, 29 Jan 2013 04:27:07 -0500 Received: from mo-p00-ob.rzone.de ([81.169.146.161]:33240 "EHLO mo-p00-ob.rzone.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752434Ab3A2J1D (ORCPT ); Tue, 29 Jan 2013 04:27:03 -0500 X-RZG-AUTH: :P2EQZWCpfu+qG7CngxMFH1J+zrwiavkK6tmQaLfmztM8TOFJii0PEz2J X-RZG-CLASS-ID: mo00 Date: Tue, 29 Jan 2013 10:26:52 +0100 From: Olaf Hering To: Jan Beulich Cc: Stefano Stabellini , KY Srinivasan , Greg KH , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] x86: Hyper-V: register clocksource only if its advertised Message-ID: <20130129092652.GA9020@aepfle.de> References: <1359121036-16309-1-git-send-email-olaf@aepfle.de> <761b736ff1854810bfe272961248e6d2@BLUPR03MB050.namprd03.prod.outlook.com> <20130125165443.GA15833@aepfle.de> <500ca90f5d3e4d4f80c7fb62c34d36f0@BLUPR03MB050.namprd03.prod.outlook.com> <20130125171923.GA19306@aepfle.de> <542f1d12e3ee46f48a85a143361c113d@SN2PR03MB061.namprd03.prod.outlook.com> <510797FA02000078000BA4B8@nat28.tlf.novell.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <510797FA02000078000BA4B8@nat28.tlf.novell.com> User-Agent: Mutt/1.5.21.rev5636 (2013-01-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 29, Jan Beulich wrote: > >>> On 28.01.13 at 18:44, Stefano Stabellini wrote: > > I think that Olaf made his point very clear: a feature A should only be > > enabled if the corresponding flag A is set. > > In fact it seems to me that this patch is correct on its own merits, > > regardless of Xen does or does not. > > > > The Xen tools might or might not know whether a guest is going to be > > Linux, Windows, FreeBSD or whatever else people use nowadays. Setting > > viridian=1 is the safe choice, given that it shouldn't create any > > issues: after all guests are supposed to check for feature flags before > > using them. > > > > If Xen is going to implement "Partition Reference Counter", it is also > > going to set the corresponding flag, so the guest OS (Windows, Linux, > > my pet OS) can check whether the feature is available and decide whether > > it wants to use it. > > While I agree in general, the specific case of the callback vector > seems a little more difficult: As KY says, there's no feature flag > for this (or perhaps more precisely for it being deliverable across > all CPUs), and hence there's both the problem of detection and > the problem of disambiguation (as otherwise both the Hyper-V > code and the Xen code in Linux could be trying to use the same > vector). This is true, but belongs to that other thread about the interrupt vector. I agree that the detection in ms_hyperv_platform() should be extended, with a DMI check for example. The patch which started this thread is still valid because it enables feature B only if the featurebit for B is enabled. Olaf