Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754245Ab0DONzR (ORCPT ); Thu, 15 Apr 2010 09:55:17 -0400 Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:41627 "EHLO www.etchedpixels.co.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753486Ab0DONzP (ORCPT ); Thu, 15 Apr 2010 09:55:15 -0400 Date: Thu, 15 Apr 2010 14:59:40 +0100 From: Alan Cox To: Michal Svoboda Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH] Kconfig: Make config Filter access to /dev/mem default y Message-ID: <20100415145940.243723b7@lxorguk.ukuu.org.uk> In-Reply-To: <20100415134152.GK21894@myhost.felk.cvut.cz> References: <20100413025228.GC10860@localhost.localdomain> <20100415063626.GG21894@myhost.felk.cvut.cz> <20100415134152.GK21894@myhost.felk.cvut.cz> X-Mailer: Claws Mail 3.7.5 (GTK+ 2.18.9; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1070 Lines: 27 On Thu, 15 Apr 2010 15:41:53 +0200 Michal Svoboda wrote: > Jiri Kosina wrote: > > Access to /dev/mem being filtered in PAT obviously applies only to x86. > > > > Architectures which don't do such filtering in their respective > > phys_mem_access_prot_allowed() still need this option. > > So why not use it for all archs uniformly? Is PAT filtering better in > some ways? PAT is an x86 specific hardware feature. The x86 processors can set per page caching properties as with some other CPU designs. In the x86 case all references to the page must have the same cache settings so the PAT implementation has to filter /dev/mem access to avoid machine check errors. It's not implemented as a security feature, its a side effect of the hardware requirements on that CPU range. Alan -- 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/