From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754728AbeCRXq6 (ORCPT ); Sun, 18 Mar 2018 19:46:58 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:52282 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754579AbeCRXqx (ORCPT ); Sun, 18 Mar 2018 19:46:53 -0400 Date: Sun, 18 Mar 2018 16:46:42 -0700 From: Ram Pai To: Thomas Gleixner Cc: Dave Hansen , linux-kernel@vger.kernel.org, linux-mm@kvack.org, dave.hansen@intel.com, mpe@ellerman.id.au, mingo@kernel.org, akpm@linux-foundation.org, shuah@kernel.org Subject: Re: [PATCH 1/3] x86, pkeys: do not special case protection key 0 Reply-To: Ram Pai References: <20180316214654.895E24EC@viggo.jf.intel.com> <20180316214656.0E059008@viggo.jf.intel.com> <20180317232425.GH1060@ram.oc3035372033.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-12-10) X-TM-AS-GCONF: 00 x-cbid: 18031823-0040-0000-0000-0000042296DF X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18031823-0041-0000-0000-00002625A8BB Message-Id: <20180318234642.GI1060@ram.oc3035372033.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-03-18_15:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1803180299 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Mar 18, 2018 at 10:30:48AM +0100, Thomas Gleixner wrote: > On Sat, 17 Mar 2018, Ram Pai wrote: > > On Fri, Mar 16, 2018 at 02:46:56PM -0700, Dave Hansen wrote: > > > > > > From: Dave Hansen > > > > > > mm_pkey_is_allocated() treats pkey 0 as unallocated. That is > > > inconsistent with the manpages, and also inconsistent with > > > mm->context.pkey_allocation_map. Stop special casing it and only > > > disallow values that are actually bad (< 0). > > > > > > The end-user visible effect of this is that you can now use > > > mprotect_pkey() to set pkey=0. > > > > > > This is a bit nicer than what Ram proposed because it is simpler > > > and removes special-casing for pkey 0. On the other hand, it does > > > allow applciations to pkey_free() pkey-0, but that's just a silly > > > thing to do, so we are not going to protect against it. > > > > So your proposal > > (a) allocates pkey 0 implicitly, > > (b) does not stop anyone from freeing pkey-0 > > (c) and allows pkey-0 to be explicitly associated with any address range. > > correct? > > > > My proposal > > (a) allocates pkey 0 implicitly, > > (b) stops anyone from freeing pkey-0 > > (c) and allows pkey-0 to be explicitly associated with any address range. > > > > So the difference between the two proposals is just the freeing part i.e (b). > > Did I get this right? > > Yes, and that's consistent with the other pkeys. > ok. Yes it makes pkey-0 even more consistent with the other keys, but not entirely consistent. pkey-0 still has the priviledge of being allocated by default. RP