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

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Message-ID: <56DDA211.20807@oracle.com>
Date:	Mon, 7 Mar 2016 08:45:21 -0700
From:	Khalid Aziz <khalid.aziz@...cle.com>
To:	Rob Gardner <rob.gardner@...cle.com>,
	David Miller <davem@...emloft.net>
Cc:	corbet@....net, akpm@...ux-foundation.org,
	dingel@...ux.vnet.ibm.com, bob.picco@...cle.com,
	kirill.shutemov@...ux.intel.com, aneesh.kumar@...ux.vnet.ibm.com,
	aarcange@...hat.com, arnd@...db.de, sparclinux@...r.kernel.org,
	mhocko@...e.cz, chris.hyser@...cle.com, richard@....at,
	vbabka@...e.cz, koct9i@...il.com, oleg@...hat.com,
	gthelen@...gle.com, jack@...e.cz, xiexiuqi@...wei.com,
	Vineet.Gupta1@...opsys.com, luto@...nel.org, ebiederm@...ssion.com,
	bsegall@...gle.com, geert@...ux-m68k.org, dave@...olabs.net,
	adobriyan@...il.com, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-arch@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH v2] sparc64: Add support for Application Data Integrity
 (ADI)

On 03/07/2016 08:30 AM, Rob Gardner wrote:
> On 03/07/2016 07:07 AM, Khalid Aziz wrote:
>> On 03/05/2016 09:07 PM, David Miller wrote:
>>> From: Khalid Aziz <khalid.aziz@...cle.com>
>>> Date: Wed,  2 Mar 2016 13:39:37 -0700
>>>
>>>>     In this
>>>>     first implementation I am enabling ADI for hugepages only
>>>>     since these pages are locked in memory and hence avoid the
>>>>     issue of saving and restoring tags.
>>>
>>> This makes the feature almost entire useless.
>>>
>>> Non-hugepages must be in the initial implementation.
>>
>> Hi David,
>>
>> Thanks for the feedback. I will get this working for non-hugepages as
>> well. ADI state of each VMA region is already stored in the VMA itself
>> in my first implementation, so I do not lose it when the page is
>> swapped out. The trouble is ADI version tags for each VMA region have
>> to be stored on the swapped out pages since the ADI version tags are
>> flushed when TLB entry for a page is flushed.
>
>
> Khalid,
>
> Are you sure about that last statement? My understanding is that the
> tags are stored in physical memory, and remain there until explicitly
> changed or removed, and so flushing a TLB entry has no effect on the ADI
> tags. If it worked the way you think, then somebody would have to
> potentially reload a long list of ADI tags on every TLB miss.
>
> Rob
>

Hi Rob,

I am fairly sure that is the case. This is what I found from the 
processor guys and others working on ADI. I tested it out by setting up 
ADI on normal malloc'd pages that got swapped out and I got MCD 
exceptions when those pages were swapped back in on access.

I mis-spoke when I said "....ADI version tags are flushed when TLB entry 
for a page is flushed". I meant ADI version tags are flushed when 
mapping for a virtual address is removed from TSB, not when TLB entry is 
flushed. Yes, ADI tags are stored in physical memory and removed when 
mapping is removed.

Thanks,
Khalid