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

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Message-ID: <c374cfc5-c895-1508-c4bb-e89df94dca53@oracle.com>
Date:   Fri, 6 Jan 2017 10:08:27 -0700
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     Rob Gardner <rob.gardner@...cle.com>, davem@...emloft.net,
        corbet@....net, arnd@...db.de, akpm@...ux-foundation.org,
        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,
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        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 01/06/2017 09:55 AM, Dave Hansen wrote:
> On 01/06/2017 08:22 AM, Khalid Aziz wrote:
>> On 01/06/2017 08:36 AM, Dave Hansen wrote:
>>> On 01/06/2017 07:32 AM, Khalid Aziz wrote:
>>>> I agree with you on simplicity first. Subpage granularity is complex,
>>>> but the architecture allows for subpage granularity. Maybe the right
>>>> approach is to support this at page granularity first for swappable
>>>> pages and then expand to subpage granularity in a subsequent patch?
>>>> Pages locked in memory can already use subpage granularity with my
>>>> patch.
>>>
>>> What do you mean by "locked in memory"?  mlock()'d memory can still be
>>> migrated around and still requires "swap" ptes, for instance.
>>
>> You are right. Page migration can invalidate subpage granularity even
>> for locked pages. Is it possible to use cpusets to keep a task and its
>> memory locked on a single node?
>
> It's going to be hard to impossible to guarantee.  mlock() doesn't
> guarantee that things won't change physical addresses.  You'd have to
> change that guarantee or chase all the things in the kernel that might
> change physical addresses (compaction, ksm, etc...).
>
> Actually, that reminds me...  How does your code interface with ksm?  Or
> is there no interaction needed since you're always working on virtual
> addresses?
>

Yes, version tags are interpreted at virtual address level.

--
Khalid