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Subject: Re: [RFC PATCH v9 03/13] mm: Add support for eXclusive Page Frame
 Ownership (XPFO)
To:     Waiman Long <longman@redhat.com>, Ingo Molnar <mingo@kernel.org>
Cc:     juergh@gmail.com, tycho@tycho.ws, jsteckli@amazon.de,
        keescook@google.com, konrad.wilk@oracle.com,
        Juerg Haefliger <juerg.haefliger@canonical.com>,
        deepa.srinivasan@oracle.com, chris.hyser@oracle.com,
        tyhicks@canonical.com, dwmw@amazon.co.uk,
        andrew.cooper3@citrix.com, jcm@redhat.com,
        boris.ostrovsky@oracle.com, iommu@lists.linux-foundation.org,
        x86@kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-security-module@vger.kernel.org,
        Khalid Aziz <khalid@gonehiking.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Dave Hansen <dave@sr71.net>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Arjan van de Ven <arjan@infradead.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
References: <cover.1554248001.git.khalid.aziz@oracle.com>
 <f1ac3700970365fb979533294774af0b0dd84b3b.1554248002.git.khalid.aziz@oracle.com>
 <20190417161042.GA43453@gmail.com>
 <e16c1d73-d361-d9c7-5b8e-c495318c2509@oracle.com>
 <35c4635e-8214-7dde-b4ec-4cb266b2ea10@redhat.com>
From:   Khalid Aziz <khalid.aziz@oracle.com>
Organization: Oracle Corp
Message-ID: <4a47cf86-a05d-3de5-0320-eda06101cc75@oracle.com>
Date:   Wed, 1 May 2019 09:18:41 -0600
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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
>=20
>> index 858b6c0b9a15..9b36da94760e 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -2997,6 +2997,12 @@
>>
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 nox2apic=C2=A0=C2=A0=C2=A0 [X86-64,APIC=
] Do not enable x2APIC mode.
>>
>> +=C2=A0=C2=A0=C2=A0 noxpfo=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 [=
XPFO] Disable eXclusive Page Frame Ownership (XPFO)
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 wh=
en CONFIG_XPFO is on. Physical pages mapped into
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 us=
er applications will also be mapped in the
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ke=
rnel's address space as if CONFIG_XPFO was not
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 en=
abled.
>> +
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 cpu0_hotplug=C2=A0=C2=A0=C2=A0 [X86] Tu=
rn on CPU0 hotplug feature when
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 CONFIG_BO OTPARAM_HOTPLUG_CPU0 is off.
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 Some features depend on CPU0. Known dependencies are:
>=20
> Given the big performance impact that XPFO can have. It should be off b=
y
> 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