linux-kernel - Re: [RFC PATCH v3] sparc64: Add support for Application Data Integrity (ADI)

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Date:   Wed, 4 Jan 2017 16:58:13 -0700
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Rob Gardner <rob.gardner@...cle.com>, davem@...emloft.net,
        corbet@....net, arnd@...db.de, akpm@...ux-foundation.org
Cc:     hpa@...or.com, viro@...iv.linux.org.uk, nitin.m.gupta@...cle.com,
        chris.hyser@...cle.com, tushar.n.dave@...cle.com,
        sowmini.varadhan@...cle.com, mike.kravetz@...cle.com,
        adam.buchbinder@...il.com, minchan@...nel.org, hughd@...gle.com,
        kirill.shutemov@...ux.intel.com, keescook@...omium.org,
        allen.pais@...cle.com, aryabinin@...tuozzo.com,
        atish.patra@...cle.com, joe@...ches.com, pmladek@...e.com,
        jslaby@...e.cz, cmetcalf@...lanox.com,
        paul.gortmaker@...driver.com, mhocko@...e.com, jmarchan@...hat.com,
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        tglx@...utronix.de, mingo@...hat.com, dan.j.williams@...el.com,
        iamjoonsoo.kim@....com, mgorman@...hsingularity.net,
        vdavydov.dev@...il.com, hannes@...xchg.org, namit@...are.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-arch@...r.kernel.org,
        x86@...nel.org, linux-mm@...ck.org,
        Khalid Aziz <khalid@...ehiking.org>
Subject: Re: [RFC PATCH v3] sparc64: Add support for Application Data
 Integrity (ADI)

On 01/04/2017 04:49 PM, Dave Hansen wrote:
> On 01/04/2017 03:44 PM, Rob Gardner wrote:
>> On 01/04/2017 03:40 PM, Dave Hansen wrote:
>>> On 01/04/2017 03:35 PM, Rob Gardner wrote:
>>>> Tags are not cleared at all when memory is freed, but rather, lazily
>>>> (and automatically) cleared when memory is allocated.
>>> What does "allocated" mean in this context?  Physical or virtual? What
>>> does this do, for instance?
>>
>> The first time a virtual page is touched by a process after the malloc,
>> the kernel does clear_user_page() or something similar, which zeroes the
>> memory. At the same time, the memory tags are cleared.
>
> OK, so the tags can't survive a MADV_FREE.  That's definitely something
> for apps to understand that use MADV_FREE as a substitute for memset().
> It also means that tags can't be set for physically unallocated memory.
>
> Neither of those are deal killers, but it would be nice to document it.

This can go into the adi.txt doc file.

>
> How does this all work with large pages?

It works with large pages the same way as normal sized pages. The TTE 
for a large page also will have the mcd bit set in it and tags are set 
and referenced the same way.

--
Khalid