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

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Date:   Wed, 4 Jan 2017 16:14:53 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Rob Gardner <rob.gardner@...cle.com>,
        Khalid Aziz <khalid.aziz@...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 04:05 PM, Rob Gardner wrote:
>> What if two different small pages have different tags and khugepaged
>> comes along and tries to collapse them?  Will the page be split if a
>> user attempts to set two different tags inside two different small-page
>> portions of a single THP?
> 
> The MCD tags operate at a resolution of cache lines (64 bytes). Page
> sizes don't matter except that each virtual page must have a bit set in
> its TTE to allow MCD to be enabled on the page. Any page can have many
> different tags, one for each cache line.

Is an "MCD tag" the same thing as a "ADI version tag"?

The thing that confused me here is that we're taking an entire page of
"ADI version tags" and stuffing them into a swap pte (in
set_swp_pte_at()).  Do we somehow have enough space in a swap pte on
sparc to fit PAGE_SIZE/64 "ADI version tag"s in there?