From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934507AbYBVMsz (ORCPT ); Fri, 22 Feb 2008 07:48:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755084AbYBVMsr (ORCPT ); Fri, 22 Feb 2008 07:48:47 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:40882 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752768AbYBVMsq (ORCPT ); Fri, 22 Feb 2008 07:48:46 -0500 Date: Fri, 22 Feb 2008 13:48:30 +0100 From: Ingo Molnar To: Joerg Roedel Cc: "H. Peter Anvin" , tglx@linutronix.de, mingo@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] X86: don't print a warning when MTRR are blank and running in KVM Message-ID: <20080222124830.GA25902@elte.hu> References: <1203605414-4958-1-git-send-email-joerg.roedel@amd.com> <20080221203748.GA9031@elte.hu> <47BDFBDE.5040102@zytor.com> <20080222094513.GA6269@elte.hu> <47BE9CB7.5070609@zytor.com> <20080222100044.GA6807@elte.hu> <20080222111518.GA6504@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080222111518.GA6504@amd.com> User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Joerg Roedel wrote: > > ok. Then i guess we should just leave the warning and the backtrace > > in place until they get a fix done? > > No. I don't agree. The MTRRs are set up by the BIOS because it knows > the hardware best (I know this is only true in theory). The OS should > basically trust the BIOS MTRR settings. If the OS can't trust the > BIOS, like on real hardware, the check and the warning is necessary. > If the OS can trust the BIOS, like running in a KVM or QEMU virtual > machine, it should just ignore the case where all MTRRs are blank. well, i can agree with the warning being pointless on KVM paravirt, but it's not pointless in the Qemu context. we fundamentall _dont_ trust the BIOS's MTRR settings, just check the very function that you modified: mtrr_trim_uncached_memory() - that function handles _exactly_ a case where a BIOS messes up MTRR's. This problem has caused real user-side breakage and just not emitting a warning because Qemu is lazy to emulate a proper PC is not a strong enough argument. so i've applied the KVM bits but the warning stays for Qemu. Ingo