From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3z0zP069M9zDqjP for ; Tue, 19 Dec 2017 11:31:48 +1100 (AEDT) Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id vBINDjRh113047 for ; Mon, 18 Dec 2017 18:16:04 -0500 Received: from e34.co.us.ibm.com (e34.co.us.ibm.com [32.97.110.152]) by mx0a-001b2d01.pphosted.com with ESMTP id 2exhukd33p-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 18 Dec 2017 18:16:03 -0500 Received: from localhost by e34.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 18 Dec 2017 16:16:02 -0700 Date: Mon, 18 Dec 2017 15:15:51 -0800 From: Ram Pai To: Dave Hansen Cc: linux-arch@vger.kernel.org, ebiederm@xmission.com, arnd@arndb.de, corbet@lwn.net, x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, mhocko@kernel.org, linux-mm@kvack.org, mingo@redhat.com, paulus@samba.org, aneesh.kumar@linux.vnet.ibm.com, linux-kselftest@vger.kernel.org, bauerman@linux.vnet.ibm.com, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, khandual@linux.vnet.ibm.com Subject: Re: [PATCH v9 29/51] mm/mprotect, powerpc/mm/pkeys, x86/mm/pkeys: Add sysfs interface Reply-To: Ram Pai References: <1509958663-18737-1-git-send-email-linuxram@us.ibm.com> <1509958663-18737-30-git-send-email-linuxram@us.ibm.com> <20171218221850.GD5461@ram.oc3035372033.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Message-Id: <20171218231551.GA5481@ram.oc3035372033.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, Dec 18, 2017 at 02:28:14PM -0800, Dave Hansen wrote: > On 12/18/2017 02:18 PM, Ram Pai wrote: > > b) minimum number of keys available to the application. > > if libraries consumes a few, they could provide a library > > interface to the application informing the number available to > > the application. The library interface can leverage (b) to > > provide the information. > > OK, let's see a real user of this including a few libraries. Then we'll > put it in the kernel. > > > c) types of disable-rights supported by keys. > > Helps the application to determine the types of disable-features > > available. This is helpful, otherwise the app has to > > make pkey_alloc() call with the corresponding parameter set > > and see if it suceeds or fails. Painful from an application > > point of view, in my opinion. > > Again, let's see a real-world use of this. How does it look? How does > an app "fall back" if it can't set a restriction the way it wants to? > > Are we *sure* that such an interface makes sense? For instance, will it > be possible for some keys to be execute-disable while other are only > write-disable? Can it be on x86? its not possible on ppc. the keys can *all* be the-same-attributes-disable all the time. However you are right. Its conceivable that some arch could provide a feature where it can be x-attribute-disable for key 'a' and y-attribute-disable for key 'b'. But than its a bit of a headache for an application to consume such a feature. Ben: I recall you requesting this feature. Thoughts? > > > I think on x86 you look for some hardware registers to determine > > which hardware features are enabled by the kernel. > > No, we use CPUID. It's a part of the ISA that's designed for > enumerating CPU and (sometimes) OS support for CPU features. > > > We do not have generic support for something like that on ppc. The > > kernel looks at the device tree to determine what hardware features > > are available. But does not have mechanism to tell the hardware to > > track which of its features are currently enabled/used by the > > kernel; atleast not for the memory-key feature. > > Bummer. You're missing out. > > But, you could still do this with a syscall. "Hey, kernel, do you > support this feature?" or do powerpc specific sysfs interface. or a debugfs interface. RP