From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758235Ab3K0XKU (ORCPT ); Wed, 27 Nov 2013 18:10:20 -0500 Received: from mail.skyhub.de ([78.46.96.112]:34577 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754213Ab3K0XKS (ORCPT ); Wed, 27 Nov 2013 18:10:18 -0500 Date: Thu, 28 Nov 2013 00:10:10 +0100 From: Borislav Petkov To: "H. Peter Anvin" Cc: Linus Torvalds , Andy Lutomirski , Andi Kleen , Linux Kernel Mailing List , Ingo Molnar , Andi Kleen , Thomas Gleixner Subject: Re: [PATCH] Add a text_poke syscall v2 Message-ID: <20131127231010.GM32267@pd.tnic> References: <1385426236-14960-1-git-send-email-andi@firstfloor.org> <5294F10C.8060901@amacapital.net> <52964EC7.9000504@zytor.com> <52966C0A.7070201@zytor.com> <20131127222104.GA748@pd.tnic> <20131127222944.GB748@pd.tnic> <529674C4.2030906@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <529674C4.2030906@zytor.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 27, 2013 at 02:40:04PM -0800, H. Peter Anvin wrote: > Also don't forget we need the IPIs, too... Yeah, I was simply looking at whether we could get away with executing an empty syscall, i.e. save us the CPUID and rely only on the IPIs and IRET. But we don't IPI ourselves in smp_call_function; actually we remove ourselves from the cpumask because of deadlocking scenarios. So on this_cpu we only execute the function with IRQs disabled and CLI/STI is not serializing. I wonder if we could use MFENCE instead of CPUID, though, and save us the clobbering of e*x, maybe even save us some cycles since MFENCE should be faster than hundred-ish cycles of microcoded CPUID. :-) -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. --