Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751394AbaJPLtX (ORCPT ); Thu, 16 Oct 2014 07:49:23 -0400 Received: from mail.skyhub.de ([78.46.96.112]:36612 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750805AbaJPLtW (ORCPT ); Thu, 16 Oct 2014 07:49:22 -0400 Date: Thu, 16 Oct 2014 13:49:17 +0200 From: Borislav Petkov To: Andy Lutomirski Cc: Peter Zijlstra , Valdis Kletnieks , "linux-kernel@vger.kernel.org" , Paul Mackerras , Arnaldo Carvalho de Melo , Ingo Molnar , Kees Cook , Andrea Arcangeli , Erik Bosman Subject: Re: [RFC 2/5] x86: Store a per-cpu shadow copy of CR4 Message-ID: <20141016114917.GD25025@nazgul.tnic> References: <808fa43ef6e24d1df47c2666174d997105b9582d.1413323611.git.luto@amacapital.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <808fa43ef6e24d1df47c2666174d997105b9582d.1413323611.git.luto@amacapital.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 14, 2014 at 03:57:36PM -0700, Andy Lutomirski wrote: > Context switches and TLB flushes can change individual bits of CR4. > CR4 reads take several cycles, so store a shadow copy of CR4 in a > per-cpu variable. > > To avoid wasting a cache line, I added the CR4 shadow to > cpu_tlbstate, which is already touched during context switches. So does this even show in any workloads as any improvement? Also, what's the rule with reading the shadow CR4? kvm only? Because svm_set_cr4() in svm.c reads the host CR4 too. Should we make all code access the shadow CR4 maybe... -- Regards/Gruss, Boris. -- -- 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/