From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932670AbbLNTGk (ORCPT ); Mon, 14 Dec 2015 14:06:40 -0500 Received: from mga03.intel.com ([134.134.136.65]:28733 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932647AbbLNTGf (ORCPT ); Mon, 14 Dec 2015 14:06:35 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.20,428,1444719600"; d="scan'208";a="707235184" Subject: [PATCH 32/32] x86, pkeys: Documentation To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, x86@kernel.org, Dave Hansen , dave.hansen@linux.intel.com From: Dave Hansen Date: Mon, 14 Dec 2015 11:06:34 -0800 References: <20151214190542.39C4886D@viggo.jf.intel.com> In-Reply-To: <20151214190542.39C4886D@viggo.jf.intel.com> Message-Id: <20151214190634.426BEE41@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Hansen Signed-off-by: Dave Hansen --- b/Documentation/x86/protection-keys.txt | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff -puN /dev/null Documentation/x86/protection-keys.txt --- /dev/null 2015-12-10 15:28:13.322405854 -0800 +++ b/Documentation/x86/protection-keys.txt 2015-12-14 10:43:30.185926457 -0800 @@ -0,0 +1,27 @@ +Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature +which will be found on future Intel CPUs. + +Memory Protection Keys provides a mechanism for enforcing page-based +protections, but without requiring modification of the page tables +when an application changes protection domains. It works by +dedicating 4 previously ignored bits in each page table entry to a +"protection key", giving 16 possible keys. + +There is also a new user-accessible register (PKRU) with two separate +bits (Access Disable and Write Disable) for each key. Being a CPU +register, PKRU is inherently thread-local, potentially giving each +thread a different set of protections from every other thread. + +There are two new instructions (RDPKRU/WRPKRU) for reading and writing +to the new register. The feature is only available in 64-bit mode, +even though there is theoretically space in the PAE PTEs. These +permissions are enforced on data access only and have no effect on +instruction fetches. + +=========================== Config Option =========================== + +This config option adds approximately 1.5kb of text. and 50 bytes of +data to the executable. A workload which does large O_DIRECT reads +of holes in XFS files was run to exercise get_user_pages_fast(). No +performance delta was observed with the config option +enabled or disabled. _