linux-kernel - Re: Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs in mind (for KVM to isolate its guests per CPU)

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Date:   Mon, 24 Sep 2018 14:45:41 +0000
From:   "Stecklina, Julian" <jsteckli@...zon.de>
To:     "khalid.aziz@...cle.com" <khalid.aziz@...cle.com>
CC:     "juerg.haefliger@....com" <juerg.haefliger@....com>,
        "deepa.srinivasan@...cle.com" <deepa.srinivasan@...cle.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
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        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "keescook@...gle.com" <keescook@...gle.com>,
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        "john.haxby@...cle.com" <john.haxby@...cle.com>,
        "jcm@...hat.com" <jcm@...hat.com>
Subject: Re: Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs
 in mind (for KVM to isolate its guests per CPU)

On Tue, 2018-09-18 at 17:00 -0600, Khalid Aziz wrote:
> I tested the kernel with this new code. When booted without
> "xpfotlbflush", 
> there is no meaningful change in system time with kernel compile. 

That's good news! So the lock optimizations seem to help.

> Kernel 
> locks up during bootup when booted with xpfotlbflush:

I didn't test the version with TLB flushes, because it's clear that the
overhead is so bad that no one wants to use this.

It shouldn't lock up though, so maybe there is still a race condition
somewhere. I'll give this a spin on my end later this week.

Thanks for trying this out!

Julian
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
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