From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752358AbdAYWVP (ORCPT ); Wed, 25 Jan 2017 17:21:15 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:31749 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751801AbdAYWVN (ORCPT ); Wed, 25 Jan 2017 17:21:13 -0500 Subject: Re: [PATCH v5 4/4] sparc64: Add support for ADI (Application Data Integrity) To: Rob Gardner , davem@davemloft.net, corbet@lwn.net References: <0b6865aabc010ee3a7ea956a70447abbab53ea70.1485362562.git.khalid.aziz@oracle.com> <154bc417-6333-f9ac-653b-9ed280f08450@oracle.com> Cc: viro@zeniv.linux.org.uk, nitin.m.gupta@oracle.com, mike.kravetz@oracle.com, akpm@linux-foundation.org, mingo@kernel.org, kirill.shutemov@linux.intel.com, adam.buchbinder@gmail.com, hughd@google.com, minchan@kernel.org, keescook@chromium.org, chris.hyser@oracle.com, atish.patra@oracle.com, cmetcalf@mellanox.com, atomlin@redhat.com, jslaby@suse.cz, joe@perches.com, paul.gortmaker@windriver.com, mhocko@suse.com, lstoakes@gmail.com, jack@suse.cz, dave.hansen@linux.intel.com, vbabka@suse.cz, dan.j.williams@intel.com, iamjoonsoo.kim@lge.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, Khalid Aziz From: Khalid Aziz Organization: Oracle Corp Message-ID: Date: Wed, 25 Jan 2017 15:20:33 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <154bc417-6333-f9ac-653b-9ed280f08450@oracle.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/25/2017 03:00 PM, Rob Gardner wrote: > On 01/25/2017 12:57 PM, Khalid Aziz wrote: >> >> @@ -157,6 +158,24 @@ int __get_user_pages_fast(unsigned long start, >> int nr_pages, int write, >> pgd_t *pgdp; >> int nr = 0; >> +#ifdef CONFIG_SPARC64 >> + if (adi_capable()) { >> + long addr = start; >> + >> + /* If userspace has passed a versioned address, kernel >> + * will not find it in the VMAs since it does not store >> + * the version tags in the list of VMAs. Storing version >> + * tags in list of VMAs is impractical since they can be >> + * changed any time from userspace without dropping into >> + * kernel. Any address search in VMAs will be done with >> + * non-versioned addresses. Ensure the ADI version bits >> + * are dropped here by sign extending the last bit before >> + * ADI bits. IOMMU does not implement version tags. >> + */ >> + addr = (addr << (long)adi_nbits()) >> (long)adi_nbits(); > > > So you are depending on the sign extension to clear the ADI bits... but > this only happens if there is a zero in that "last bit before ADI bits". > If the last bit is a 1, then the ADI bits will be set instead of > cleared. That seems like an unintended consequence given the comment. I > am aware of the value of adi_nbits() and of the number of valid bits in > a virtual address on the M7 processor, but wouldn't using 'unsigned > long' for everything here guarantee the ADI bits get cleared regardless > of the state of the last non-adi bit? Sign extension is the right thing to do. MMU considers values of 0 and 15 for bits 63-60 to be untagged addresses and expects bit 59 to be sign-extended for untagged virtual addresses. The code I added is explicitly meant to sign-extend, not zero out the top 4 bits. -- Khalid From mboxrd@z Thu Jan 1 00:00:00 1970 From: Khalid Aziz Date: Wed, 25 Jan 2017 22:20:33 +0000 Subject: Re: [PATCH v5 4/4] sparc64: Add support for ADI (Application Data Integrity) Message-Id: List-Id: References: <0b6865aabc010ee3a7ea956a70447abbab53ea70.1485362562.git.khalid.aziz@oracle.com> <154bc417-6333-f9ac-653b-9ed280f08450@oracle.com> In-Reply-To: <154bc417-6333-f9ac-653b-9ed280f08450@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Rob Gardner , davem@davemloft.net, corbet@lwn.net Cc: viro@zeniv.linux.org.uk, nitin.m.gupta@oracle.com, mike.kravetz@oracle.com, akpm@linux-foundation.org, mingo@kernel.org, kirill.shutemov@linux.intel.com, adam.buchbinder@gmail.com, hughd@google.com, minchan@kernel.org, keescook@chromium.org, chris.hyser@oracle.com, atish.patra@oracle.com, cmetcalf@mellanox.com, atomlin@redhat.com, jslaby@suse.cz, joe@perches.com, paul.gortmaker@windriver.com, mhocko@suse.com, lstoakes@gmail.com, jack@suse.cz, dave.hansen@linux.intel.com, vbabka@suse.cz, dan.j.williams@intel.com, iamjoonsoo.kim@lge.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, Khalid Aziz On 01/25/2017 03:00 PM, Rob Gardner wrote: > On 01/25/2017 12:57 PM, Khalid Aziz wrote: >> >> @@ -157,6 +158,24 @@ int __get_user_pages_fast(unsigned long start, >> int nr_pages, int write, >> pgd_t *pgdp; >> int nr = 0; >> +#ifdef CONFIG_SPARC64 >> + if (adi_capable()) { >> + long addr = start; >> + >> + /* If userspace has passed a versioned address, kernel >> + * will not find it in the VMAs since it does not store >> + * the version tags in the list of VMAs. Storing version >> + * tags in list of VMAs is impractical since they can be >> + * changed any time from userspace without dropping into >> + * kernel. Any address search in VMAs will be done with >> + * non-versioned addresses. Ensure the ADI version bits >> + * are dropped here by sign extending the last bit before >> + * ADI bits. IOMMU does not implement version tags. >> + */ >> + addr = (addr << (long)adi_nbits()) >> (long)adi_nbits(); > > > So you are depending on the sign extension to clear the ADI bits... but > this only happens if there is a zero in that "last bit before ADI bits". > If the last bit is a 1, then the ADI bits will be set instead of > cleared. That seems like an unintended consequence given the comment. I > am aware of the value of adi_nbits() and of the number of valid bits in > a virtual address on the M7 processor, but wouldn't using 'unsigned > long' for everything here guarantee the ADI bits get cleared regardless > of the state of the last non-adi bit? Sign extension is the right thing to do. MMU considers values of 0 and 15 for bits 63-60 to be untagged addresses and expects bit 59 to be sign-extended for untagged virtual addresses. The code I added is explicitly meant to sign-extend, not zero out the top 4 bits. -- Khalid From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id C072A6B0033 for ; Wed, 25 Jan 2017 17:20:56 -0500 (EST) Received: by mail-pf0-f199.google.com with SMTP id d123so33747056pfd.0 for ; Wed, 25 Jan 2017 14:20:56 -0800 (PST) Received: from aserp1040.oracle.com (aserp1040.oracle.com. [141.146.126.69]) by mx.google.com with ESMTPS id b59si2863898plc.240.2017.01.25.14.20.55 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 25 Jan 2017 14:20:55 -0800 (PST) Subject: Re: [PATCH v5 4/4] sparc64: Add support for ADI (Application Data Integrity) References: <0b6865aabc010ee3a7ea956a70447abbab53ea70.1485362562.git.khalid.aziz@oracle.com> <154bc417-6333-f9ac-653b-9ed280f08450@oracle.com> From: Khalid Aziz Message-ID: Date: Wed, 25 Jan 2017 15:20:33 -0700 MIME-Version: 1.0 In-Reply-To: <154bc417-6333-f9ac-653b-9ed280f08450@oracle.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Rob Gardner , davem@davemloft.net, corbet@lwn.net Cc: viro@zeniv.linux.org.uk, nitin.m.gupta@oracle.com, mike.kravetz@oracle.com, akpm@linux-foundation.org, mingo@kernel.org, kirill.shutemov@linux.intel.com, adam.buchbinder@gmail.com, hughd@google.com, minchan@kernel.org, keescook@chromium.org, chris.hyser@oracle.com, atish.patra@oracle.com, cmetcalf@mellanox.com, atomlin@redhat.com, jslaby@suse.cz, joe@perches.com, paul.gortmaker@windriver.com, mhocko@suse.com, lstoakes@gmail.com, jack@suse.cz, dave.hansen@linux.intel.com, vbabka@suse.cz, dan.j.williams@intel.com, iamjoonsoo.kim@lge.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, Khalid Aziz On 01/25/2017 03:00 PM, Rob Gardner wrote: > On 01/25/2017 12:57 PM, Khalid Aziz wrote: >> >> @@ -157,6 +158,24 @@ int __get_user_pages_fast(unsigned long start, >> int nr_pages, int write, >> pgd_t *pgdp; >> int nr = 0; >> +#ifdef CONFIG_SPARC64 >> + if (adi_capable()) { >> + long addr = start; >> + >> + /* If userspace has passed a versioned address, kernel >> + * will not find it in the VMAs since it does not store >> + * the version tags in the list of VMAs. Storing version >> + * tags in list of VMAs is impractical since they can be >> + * changed any time from userspace without dropping into >> + * kernel. Any address search in VMAs will be done with >> + * non-versioned addresses. Ensure the ADI version bits >> + * are dropped here by sign extending the last bit before >> + * ADI bits. IOMMU does not implement version tags. >> + */ >> + addr = (addr << (long)adi_nbits()) >> (long)adi_nbits(); > > > So you are depending on the sign extension to clear the ADI bits... but > this only happens if there is a zero in that "last bit before ADI bits". > If the last bit is a 1, then the ADI bits will be set instead of > cleared. That seems like an unintended consequence given the comment. I > am aware of the value of adi_nbits() and of the number of valid bits in > a virtual address on the M7 processor, but wouldn't using 'unsigned > long' for everything here guarantee the ADI bits get cleared regardless > of the state of the last non-adi bit? Sign extension is the right thing to do. MMU considers values of 0 and 15 for bits 63-60 to be untagged addresses and expects bit 59 to be sign-extended for untagged virtual addresses. The code I added is explicitly meant to sign-extend, not zero out the top 4 bits. -- Khalid -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org