linux-kernel - Re: [RFC PATCH v9 03/13] mm: Add support for eXclusive Page Frame Ownership (XPFO)

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Date:   Wed, 1 May 2019 09:18:41 -0600
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...nel.org>
Cc:     juergh@...il.com, tycho@...ho.ws, jsteckli@...zon.de,
        keescook@...gle.com, konrad.wilk@...cle.com,
        Juerg Haefliger <juerg.haefliger@...onical.com>,
        deepa.srinivasan@...cle.com, chris.hyser@...cle.com,
        tyhicks@...onical.com, dwmw@...zon.co.uk,
        andrew.cooper3@...rix.com, jcm@...hat.com,
        boris.ostrovsky@...cle.com, iommu@...ts.linux-foundation.org,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-security-module@...r.kernel.org,
        Khalid Aziz <khalid@...ehiking.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Dave Hansen <dave@...1.net>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Arjan van de Ven <arjan@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [RFC PATCH v9 03/13] mm: Add support for eXclusive Page Frame
 Ownership (XPFO)

On 5/1/19 8:49 AM, Waiman Long wrote:
> On Wed, Apr 03, 2019 at 11:34:04AM -0600, Khalid Aziz wrote:
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> 
>> index 858b6c0b9a15..9b36da94760e 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -2997,6 +2997,12 @@
>>
>>       nox2apic    [X86-64,APIC] Do not enable x2APIC mode.
>>
>> +    noxpfo        [XPFO] Disable eXclusive Page Frame Ownership (XPFO)
>> +            when CONFIG_XPFO is on. Physical pages mapped into
>> +            user applications will also be mapped in the
>> +            kernel's address space as if CONFIG_XPFO was not
>> +            enabled.
>> +
>>       cpu0_hotplug    [X86] Turn on CPU0 hotplug feature when
>>               CONFIG_BO OTPARAM_HOTPLUG_CPU0 is off.
>>               Some features depend on CPU0. Known dependencies are:
> 
> Given the big performance impact that XPFO can have. It should be off by
> default when configured. Instead, the xpfo option should be used to
> enable it.

Agreed. I plan to disable it by default in the next version of the
patch. This is likely to end up being a feature for extreme security
conscious folks only, unless I or someone else comes up with further
significant performance boost.

Thanks,
Khalid