Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751826AbWIRQY4 (ORCPT ); Mon, 18 Sep 2006 12:24:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751829AbWIRQY4 (ORCPT ); Mon, 18 Sep 2006 12:24:56 -0400 Received: from gw.goop.org ([64.81.55.164]:57771 "EHLO mail.goop.org") by vger.kernel.org with ESMTP id S1751826AbWIRQYz (ORCPT ); Mon, 18 Sep 2006 12:24:55 -0400 Message-ID: <450EC855.6020200@goop.org> Date: Mon, 18 Sep 2006 09:24:53 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 1.5.0.7 (X11/20060913) MIME-Version: 1.0 To: Linus Torvalds CC: Andi Kleen , Andrew Morton , Chuck Ebbert <76306.1226@compuserve.com>, In Cognito , linux-kernel , Ingo Molnar , bcrl@kvack.org, Zachary Amsden , Rusty Russell , Chris Wright , Jeremy Fitzhardinge Subject: Re: Sysenter crash with Nested Task Bit set References: <200609172354_MC3-1-CB7A-58ED@compuserve.com> <20060917222537.55241d19.akpm@osdl.org> <200609181729.23934.ak@suse.de> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1370 Lines: 31 Linus Torvalds wrote: > Final note (I promise): now that we save/restore eflags again, we > should probably revert the set_iopl_mask() in task switching too. However, > that apparently has some para-virtualization issues, so I'm going to > ignore that part from now. > I'm wondering if we shouldn't have a (__)switch_to paravirt hook, so we can wrap the context switch in whatever we like. > However, I'd really like people who know and care about the > paravirtualization to take a good long look at it: because right now, with > the addition of the eflags save/restore, the set_iopl_mask() in > __switch_to() is entirely useless for non-virtualized environments, afaik. > Hm. Zach removed the pushf/popf in switch_to this last Sept, with the comment "The pushf/popf in switch_to are ONLY used to switch IOPL. Making this explicit in C code is more clear. This pushf/popf pair was added as a bugfix for leaking IOPL to unprivileged processes when using sysenter/sysexit based system calls (sysexit does not restore flags)." > Zack added to the cc. Who else needs to know? Rusty, Chris Wright and 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/