From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932633AbdAIJMo (ORCPT ); Mon, 9 Jan 2017 04:12:44 -0500 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:32967 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752864AbdAIJMm (ORCPT ); Mon, 9 Jan 2017 04:12:42 -0500 Date: Mon, 9 Jan 2017 10:12:38 +0100 From: Pavel Machek To: Thomas Gleixner Cc: Grzegorz Andrejczuk , mingo@redhat.com, hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org, Piotr.Luc@intel.com, dave.hansen@linux.intel.com Subject: Re: [PATCH v11 0/5] Enabling Ring 3 MONITOR/MWAIT feature for Knights Landing Message-ID: <20170109091238.GA19679@amd> References: <1482241726-27310-1-git-send-email-grzegorz.andrejczuk@intel.com> <20170103220935.GB22548@amd> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="45Z9DzgjV8m4Oswq" Content-Disposition: inline In-Reply-To: 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 --45Z9DzgjV8m4Oswq Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon 2017-01-09 09:59:42, Thomas Gleixner wrote: > On Tue, 3 Jan 2017, Pavel Machek wrote: >=20 > > On Tue 2016-12-20 14:48:41, Grzegorz Andrejczuk wrote: > > > Following patches enable the use of the feature that allows > > > the Intel Xeon Phi x200 devices to use MONITOR/MWAIT instructions > > > outside ring 0. It allows userspace applications to use > > > more efficient synchronization operations, which improves performance > > > and energy efficiency. > >=20 > > What kind of security holes does it bring us? > >=20 > > rdseed can be used for two processes to communicate when they should > > not (serious problem for android). Can this be used for something simil= ar? >=20 > No. The monitor address must be in the virtual address space of the > caller, so it's like any other 'read' operation. Hmm. Unlike any other 'read' operation, it allows userland to modulate CPU frequency with great precision; probably allowing userland to transmit at radio bands, and allowing sound production without syscalls (singing capacitors). But userland can probably do that already, with help of high-resolution timers, so nothing new theree... that I can think off. Lets wait for the presentation at 39c3 :-). Pavel --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html --45Z9DzgjV8m4Oswq Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEARECAAYFAlhzVAYACgkQMOfwapXb+vIIQQCeORUbPcXwKmqxxU1slBF1dNFn kr0An1Hc6n1tzjJPR7Z9QWg3CBsoONa2 =+LxX -----END PGP SIGNATURE----- --45Z9DzgjV8m4Oswq--