From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758783Ab2K3RCQ (ORCPT ); Fri, 30 Nov 2012 12:02:16 -0500 Received: from mail-we0-f174.google.com ([74.125.82.174]:64293 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932621Ab2K3RCM (ORCPT ); Fri, 30 Nov 2012 12:02:12 -0500 MIME-Version: 1.0 In-Reply-To: <50B7D28A.4000401@linux.intel.com> References: <1354132230-21854-1-git-send-email-hpa@linux.intel.com> <1354132230-21854-9-git-send-email-hpa@linux.intel.com> <20121128204158.GC14635@liondog.tnic> <50B7D28A.4000401@linux.intel.com> From: Linus Torvalds Date: Fri, 30 Nov 2012 09:01:50 -0800 X-Google-Sender-Auth: fChoGjZ3xPHCIrjX4OiP6k4ilFM Message-ID: Subject: Re: [PATCH 8/8] x86, cleanups: Simplify sync_core() in the case of no CPUID To: "H. Peter Anvin" Cc: Borislav Petkov , "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , Linux Kernel Mailing List , Mario Gzuk Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 29, 2012 at 1:24 PM, H. Peter Anvin wrote: > > Thinking about it some more, there is another reason to not do this, > which is that we don't want this particular CPUID to be paravirtualized; > we're after the synchronizing side effect, not the CPUID return value > itself. > > So let's leave it as a primitive; it gets too confusing otherwise. Hmm. The virtualization issue brings up another point: do we *really* want to use cpuid for serialization at all? Exactly because under _real_ virtualization (as opposed to para-virt), it can cause unnecessary exits in a virtualized environment, no? So I'm wondering if there is any better synchronizing instruction.. I guess sync_core() isn't used *that* much, so maybe we don't care, but I thought I'd ask... Linus