From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f70.google.com (mail-it0-f70.google.com [209.85.214.70]) by kanga.kvack.org (Postfix) with ESMTP id C32096B0033 for ; Wed, 25 Jan 2017 17:57:58 -0500 (EST) Received: by mail-it0-f70.google.com with SMTP id o185so25976831itb.6 for ; Wed, 25 Jan 2017 14:57:58 -0800 (PST) Received: from userp1040.oracle.com (userp1040.oracle.com. [156.151.31.81]) by mx.google.com with ESMTPS id k188si363437ita.95.2017.01.25.14.57.57 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 25 Jan 2017 14:57:58 -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> <19f33a99-e719-a2a5-4330-390ed7755315@oracle.com> From: Khalid Aziz Message-ID: <97f5ad25-432c-f536-d2af-681288b7cca1@oracle.com> Date: Wed, 25 Jan 2017 15:57:36 -0700 MIME-Version: 1.0 In-Reply-To: <19f33a99-e719-a2a5-4330-390ed7755315@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 03:50 PM, Rob Gardner wrote: > On 01/25/2017 03:20 PM, Khalid Aziz wrote: >> 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. > > OK, that wasn't perfectly clear from the comment, which said "version > bits are dropped". > > So sign extending will produce an address that the MMU can use, but will > it produce an address that will allow a successful search in the page > tables? ie, was this same sign extending done when first handing out > that virtual address to the user? > Yes to both your questions. When virtual addresses are handed out, the last implemented virtual address bit is sign-extended. Sign-extending when dropping version bits preserves that original sign-extension. This is why MMU considers tag values of 0 as well as 15 to be invalid because they both represent sign-extension of the last implemented virtual address. -- 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