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[209.132.180.67]) by mx.google.com with ESMTP id t9si3550058pfh.101.2018.03.15.02.47.32; Thu, 15 Mar 2018 02:47:47 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751597AbeCOJqg (ORCPT + 99 others); Thu, 15 Mar 2018 05:46:36 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:52928 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751314AbeCOJqf (ORCPT ); Thu, 15 Mar 2018 05:46:35 -0400 Received: from hsi-kbw-5-158-153-52.hsi19.kabel-badenwuerttemberg.de ([5.158.153.52] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1ewPSY-0005TL-6k; Thu, 15 Mar 2018 10:46:06 +0100 Date: Thu, 15 Mar 2018 10:46:05 +0100 (CET) From: Thomas Gleixner 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 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> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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