Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752975Ab0AQAM4 (ORCPT ); Sat, 16 Jan 2010 19:12:56 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751663Ab0AQAMz (ORCPT ); Sat, 16 Jan 2010 19:12:55 -0500 Received: from ey-out-2122.google.com ([74.125.78.25]:40397 "EHLO ey-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750743Ab0AQAMy convert rfc822-to-8bit (ORCPT ); Sat, 16 Jan 2010 19:12:54 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type:content-transfer-encoding; b=TyqsxwqvhuroVilMGxxxg8QK++I6oAkMlwQEqW161m9ib6fchOQdHC+eN8EN2UaK8G Y29h5Sz5baGxGQiq2PEmeZzrWhF8JUSNq6QBsdk+Y5JRdWbogOfl5zK0VlIhchhUA8C0 C/+6WfPixtkJFauhaXn5TJllAsMG5sZUfPY2k= MIME-Version: 1.0 In-Reply-To: <1263603503.5007.134.camel@localhost.localdomain> References: <20100111122521.22050.3654.sendpatchset@srikar.in.ibm.com> <20100111122529.22050.32596.sendpatchset@srikar.in.ibm.com> <1263467289.4244.288.camel@laptop> <1263498366.4875.25.camel@localhost.localdomain> <1263546175.4244.342.camel@laptop> <1263589634.5007.34.camel@localhost.localdomain> <1263592192.4244.488.camel@laptop> <1263603503.5007.134.camel@localhost.localdomain> From: Bryan Donlan Date: Sat, 16 Jan 2010 19:12:28 -0500 Message-ID: <3e8340491001161612x11873abdi4b74e47309e5bdfd@mail.gmail.com> Subject: Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP) To: Jim Keniston Cc: Peter Zijlstra , Srikar Dronamraju , Ingo Molnar , Arnaldo Carvalho de Melo , Ananth N Mavinakayanahalli , utrace-devel , Frederic Weisbecker , Masami Hiramatsu , Maneesh Soni , Mark Wielaard , LKML Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1426 Lines: 25 On Fri, Jan 15, 2010 at 7:58 PM, Jim Keniston wrote: > 4. Emulation removes the need for the XOL area, but requires pretty much > total knowledge of the instruction set. ?It's also a performance win for > architectures that can't do #3. ?I see kvm implemented on 4 > architectures (ia64, powerpc, s390, x86). ?Coincidentally, those are the > architectures to which uprobes (old uprobes, with ubp and xol bundled > in) has already been ported (though Intel hasn't been maintaining their > ia64 port). ?So it sort of comes down to how objectionable the XOL vma > (or page) really is. On x86 at least, wouldn't one option to be to run the instruction to be emulated in CPL ('ring') 2, from a XOL page above the user-kernel split, not accessible to userspace at CPL 3? Linux hasn't traditionally used anything other than CPL 0 and CPL 3 (plus CPL 1 on Xen), but it would seem to avoid many of the problems here - it's invisible to normal userspace code and so doesn't pollute userspace memory maps with kernel-private stuff, but since it's running at a higher CPL than the kernel, we can still protect kernel memory and protect against privileged instructions. -- 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/