From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id DDC006B0005 for ; Thu, 15 Mar 2018 05:46:27 -0400 (EDT) Received: by mail-wm0-f71.google.com with SMTP id i64so2236498wmd.8 for ; Thu, 15 Mar 2018 02:46:27 -0700 (PDT) Received: from Galois.linutronix.de (Galois.linutronix.de. [2a01:7a0:2:106d:700::1]) by mx.google.com with ESMTPS id n23si3362753wrf.404.2018.03.15.02.46.26 for (version=TLS1_2 cipher=AES128-SHA bits=128/128); Thu, 15 Mar 2018 02:46:26 -0700 (PDT) Date: Thu, 15 Mar 2018 10:46:05 +0100 (CET) From: Thomas Gleixner Subject: Re: [PATCH v3] x86: treat pkey-0 special In-Reply-To: <1521061214-22385-1-git-send-email-linuxram@us.ibm.com> Message-ID: References: <1521061214-22385-1-git-send-email-linuxram@us.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Ram Pai Cc: mingo@redhat.com, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, dave.hansen@intel.com, benh@kernel.crashing.org, paulus@samba.org, khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com, bsingharora@gmail.com, hbabu@us.ibm.com, mhocko@kernel.org, bauerman@linux.vnet.ibm.com, ebiederm@xmission.com, corbet@lwn.net, arnd@arndb.de, fweimer@redhat.com, msuchanek@suse.com, Ulrich.Weigand@de.ibm.com On Wed, 14 Mar 2018, Ram Pai wrote: > Applications need the ability to associate an address-range with some > key and latter revert to its initial default key. Pkey-0 comes close to > providing this function but falls short, because the current > implementation disallows applications to explicitly associate pkey-0 to > the address range. > > This patch clarifies the semantics of pkey-0 and provides the grep 'This patch' Documentation/process > corresponding implementation on powerpc. > > Pkey-0 is special with the following semantics. > (a) it is implicitly allocated and can never be freed. It always exists. > (b) it is the default key assigned to any address-range. > (c) it can be explicitly associated with any address-range. > > Tested on x86_64. I'm curious how the corresponding implementation on powerpc can be tested on x86_64. Copy and paste is not enough ... > > History: > v3 : added clarification of the semantics of pkey0. > -- suggested by Dave Hansen > v2 : split the patch into two, one for x86 and one for powerpc > -- suggested by Michael Ellermen Please put the history below the --- seperator. It's not part of the changelog. That way the tools can discard it when picking up the patch. > > cc: Dave Hansen > cc: Michael Ellermen > cc: Ingo Molnar > Signed-off-by: Ram Pai > --- > arch/x86/include/asm/pkeys.h | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/pkeys.h b/arch/x86/include/asm/pkeys.h > index a0ba1ff..6ea7486 100644 > --- a/arch/x86/include/asm/pkeys.h > +++ b/arch/x86/include/asm/pkeys.h > @@ -52,7 +52,7 @@ bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey) > * from pkey_alloc(). pkey 0 is special, and never > * returned from pkey_alloc(). > */ > - if (pkey <= 0) > + if (pkey < 0) > return false; > if (pkey >= arch_max_pkey()) > return false; > @@ -92,7 +92,8 @@ int mm_pkey_alloc(struct mm_struct *mm) > static inline > int mm_pkey_free(struct mm_struct *mm, int pkey) > { > - if (!mm_pkey_is_allocated(mm, pkey)) > + /* pkey 0 is special and can never be freed */ This comment is pretty useless. How should anyone figure out whats special about pkey 0? > + if (!pkey || !mm_pkey_is_allocated(mm, pkey)) Why this extra check? mm_pkey_is_allocated(mm, 0) should not return true ever. If it does, then this wants to be fixed. Thanks, tglx