linux-kernel - Re: [PATCH v2] sparc64: Add support for Application Data Integrity (ADI)

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Message-ID: <56DDED63.8010302@oracle.com>
Date:	Mon, 7 Mar 2016 14:06:43 -0700
From:	Khalid Aziz <khalid.aziz@...cle.com>
To:	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...capital.net>,
	Rob Gardner <rob.gardner@...cle.com>
Cc:	David Miller <davem@...emloft.net>,
	Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	dingel@...ux.vnet.ibm.com, zhenzhang.zhang@...wei.com,
	bob.picco@...cle.com,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Arnd Bergmann <arnd@...db.de>, sparclinux@...r.kernel.org,
	Michal Hocko <mhocko@...e.cz>, chris.hyser@...cle.com,
	Richard Weinberger <richard@....at>,
	Vlastimil Babka <vbabka@...e.cz>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Greg Thelen <gthelen@...gle.com>, Jan Kara <jack@...e.cz>,
	xiexiuqi@...wei.com, Vineet.Gupta1@...opsys.com,
	Andrew Lutomirski <luto@...nel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, bsegall@...gle.com,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2] sparc64: Add support for Application Data Integrity
 (ADI)

On 03/07/2016 10:46 AM, Dave Hansen wrote:
> On 03/07/2016 08:06 AM, Khalid Aziz wrote:
>> Top 4-bits of sparc64 virtual address are used for version tag only when
>> a process has its PSTATE.mcde bit set and it is accessing a memory
>> region that has ADI enabled on it (TTE.mcd set) and a version tag was
>> set on the virtual address being accessed. These 4-bits retain their
>> original semantics in all other cases.
>
> OK, so this effectively reduces the address space of a process using the
> feature.  Do we need to do anything explicit to keep an app from using
> that address space?  Do we make sure the kernel doesn't place VMAs
> there?  Do we respect mmap() hints that try to place memory there?
>

Good questions. Isn't set of valid VAs already constrained by VA_BITS 
(set to 44 in arch/sparc/include/asm/processor_64.h)? As I see it we are 
already not using the top 4 bits. Please correct me if I am wrong.

Thanks,
Khalid