From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f47.google.com (mail-pa0-f47.google.com [209.85.220.47]) by kanga.kvack.org (Postfix) with ESMTP id B43CE6B027A for ; Mon, 14 Dec 2015 14:06:53 -0500 (EST) Received: by pabur14 with SMTP id ur14so108617960pab.0 for ; Mon, 14 Dec 2015 11:06:53 -0800 (PST) Received: from mga04.intel.com (mga04.intel.com. [192.55.52.120]) by mx.google.com with ESMTP id la15si11637192pab.205.2015.12.14.11.06.34 for ; Mon, 14 Dec 2015 11:06:34 -0800 (PST) Subject: [PATCH 32/32] x86, pkeys: Documentation 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: owner-linux-mm@kvack.org List-ID: To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, x86@kernel.org, Dave Hansen , dave.hansen@linux.intel.com 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. _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org