Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966731AbWKOKBV (ORCPT ); Wed, 15 Nov 2006 05:01:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S966732AbWKOKBV (ORCPT ); Wed, 15 Nov 2006 05:01:21 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:6577 "EHLO mx2.mail.elte.hu") by vger.kernel.org with ESMTP id S966731AbWKOKBU (ORCPT ); Wed, 15 Nov 2006 05:01:20 -0500 Date: Wed, 15 Nov 2006 11:00:30 +0100 From: Ingo Molnar To: Andi Kleen Cc: Steven Rostedt , patches@x86-64.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH for 2.6.19] [3/9] x86_64: shorten the x86_64 boot setup GDT to what the comment says Message-ID: <20061115100030.GA5753@elte.hu> References: <20061114508.445749000@suse.de> <20061114160853.9F16213C98@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20061114160853.9F16213C98@wotan.suse.de> User-Agent: Mutt/1.4.2.2i X-ELTE-SpamScore: -2.8 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.8 required=5.9 tests=ALL_TRUSTED,AWL,BAYES_50 autolearn=no SpamAssassin version=3.0.3 -3.3 ALL_TRUSTED Did not pass through any untrusted hosts 0.5 BAYES_50 BODY: Bayesian spam probability is 40 to 60% [score: 0.4998] -0.0 AWL AWL: From: address is in the auto white-list X-ELTE-VirusStatus: clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1635 Lines: 38 > From: Steven Rostedt > > Stephen Tweedie, Herbert Xu, and myself have been struggling with a very > nasty bug in Xen. But it also pointed out a small bug in the x86_64 > kernel boot setup. > > The GDT limit being setup by the initial bzImage code when entering into > protected mode is way too big. The comment by the code states that the > size of the GDT is 2048, but the actual size being set up is much bigger > (32768). This happens simply because of one extra '0'. > > Instead of setting up a 0x800 size, 0x8000 is set up. On bare metal this > is fine because the CPU wont load any segments unless they are > explicitly used. But unfortunately, this breaks Xen on vmx FV, since it > (for now) blindly loads all the segments into the VMCS if they are less > than the gdt limit. Since the real mode segments are around 0x3000, we are > getting junk into the VMCS and that later causes an exception. > > Stephen Tweedie has written up a patch to fix the Xen side and will be > submitting that to those folks. But that doesn't excuse the GDT limit > being a magnitude too big. > > AK: changed to compute true gdt size in assembler, fixed comment > > Signed-off-by: Steven Rostedt > Signed-off-by: Andi Kleen Acked-by: Ingo Molnar note, it seems to me that i386 had this fix years ago already. Ingo - 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/