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 3z1Njg0ybmzDx63 for ; Wed, 20 Dec 2017 03:32:38 +1100 (AEDT) Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id vBJGWPHN135041 for ; Tue, 19 Dec 2017 11:32:36 -0500 Received: from e17.ny.us.ibm.com (e17.ny.us.ibm.com [129.33.205.207]) by mx0a-001b2d01.pphosted.com with ESMTP id 2ey63rgw2s-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 19 Dec 2017 11:32:36 -0500 Received: from localhost by e17.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 19 Dec 2017 11:32:34 -0500 Date: Tue, 19 Dec 2017 08:32:25 -0800 From: Ram Pai To: Michael Ellerman Cc: Dave Hansen , mingo@redhat.com, akpm@linux-foundation.org, corbet@lwn.net, arnd@arndb.de, linux-arch@vger.kernel.org, ebiederm@xmission.com, linux-doc@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, mhocko@kernel.org, linux-mm@kvack.org, paulus@samba.org, aneesh.kumar@linux.vnet.ibm.com, linux-kselftest@vger.kernel.org, bauerman@linux.vnet.ibm.com, 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> <877etj9ekv.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <877etj9ekv.fsf@concordia.ellerman.id.au> Message-Id: <20171219163225.GC5481@ram.oc3035372033.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Dec 19, 2017 at 09:50:24PM +1100, Michael Ellerman wrote: > Dave Hansen writes: > > > On 11/06/2017 12:57 AM, Ram Pai wrote: > >> Expose useful information for programs using memory protection keys. > >> Provide implementation for powerpc and x86. > >> > >> On a powerpc system with pkeys support, here is what is shown: > >> > >> $ head /sys/kernel/mm/protection_keys/* > >> ==> /sys/kernel/mm/protection_keys/disable_access_supported <== > >> true > > > > This is cute, but I don't think it should be part of the ABI. Put it in > > debugfs if you want it for cute tests. The stuff that this tells you > > can and should come from pkey_alloc() for the ABI. > > Yeah I agree this is not sysfs material. > > In particular the total/usable numbers are completely useless vs other > threads allocating pkeys out from under you. The usable number is the minimum number of keys available for use by the application, not the number of keys **currently** available. Its a static number. I am dropping this patch. We can revisit this when a clear request for such a feature emerges. > > > > >> Any application wanting to use protection keys needs to be able to > >> function without them. They might be unavailable because the > >> hardware that the application runs on does not support them, the > >> kernel code does not contain support, the kernel support has been > >> disabled, or because the keys have all been allocated, perhaps by a > >> library the application is using. It is recommended that > >> applications wanting to use protection keys should simply call > >> pkey_alloc(2) and test whether the call succeeds, instead of > >> attempting to detect support for the feature in any other way. > > > > Do you really not have standard way on ppc to say whether hardware > > features are supported by the kernel? For instance, how do you know if > > a given set of registers are known to and are being context-switched by > > the kernel? > > Yes we do, we emit feature bits in the AT_HWCAP entry of the aux vector, > same as some other architectures. Ah. I was not aware of this. Thanks, RP