From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id C9D796B0003 for ; Sun, 18 Mar 2018 19:46:55 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id h33so8608995wrh.10 for ; Sun, 18 Mar 2018 16:46:55 -0700 (PDT) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id k17si1250549edf.419.2018.03.18.16.46.53 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 18 Mar 2018 16:46:53 -0700 (PDT) Received: from pps.filterd (m0098420.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w2INiI9X099876 for ; Sun, 18 Mar 2018 19:46:52 -0400 Received: from e06smtp10.uk.ibm.com (e06smtp10.uk.ibm.com [195.75.94.106]) by mx0b-001b2d01.pphosted.com with ESMTP id 2gsxhfvrp2-1 (version=TLSv1.2 cipher=AES256-SHA256 bits=256 verify=NOT) for ; Sun, 18 Mar 2018 19:46:52 -0400 Received: from localhost by e06smtp10.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sun, 18 Mar 2018 23:46:50 -0000 Date: Sun, 18 Mar 2018 16:46:42 -0700 From: Ram Pai 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: Message-Id: <20180318234642.GI1060@ram.oc3035372033.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: 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 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