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From: Tycho Andersen <tycho@tycho.ws>
To: Julian Stecklina <jsteckli@amazon.de>
Cc: Juerg Haefliger <juergh@gmail.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	David Woodhouse <dwmw@amazon.co.uk>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	deepa.srinivasan@oracle.com, Jim Mattson <jmattson@google.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	linux-mm <linux-mm@kvack.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	joao.m.martins@oracle.com, pradeep.vincent@oracle.com,
	Andi Kleen <ak@linux.intel.com>,
	Khalid Aziz <khalid.aziz@oracle.com>,
	kanth.ghatraju@oracle.com, Liran Alon <liran.alon@oracle.com>,
	Kees Cook <keescook@google.com>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	chris.hyser@oracle.com, Tyler Hicks <tyhicks@canonical.com>,
	John Haxby <john.haxby@oracle.com>, Jon Masters <jcm@redhat.com>
Subject: Re: Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs in mind (for KVM to isolate its guests per CPU)
Date: Mon, 17 Sep 2018 04:19:50 -0600	[thread overview]
Message-ID: <20180917101950.GG4672@cisco> (raw)
In-Reply-To: <ciirm8r2hs30kh.fsf@u54ee758033e858cfa736.ant.amazon.com>

On Mon, Sep 17, 2018 at 12:01:02PM +0200, Julian Stecklina wrote:
> Juerg Haefliger <juergh@gmail.com> writes:
> 
> >> I've updated my XPFO branch[1] to make some of the debugging optional
> >> and also integrated the XPFO bookkeeping with struct page, instead of
> >> requiring CONFIG_PAGE_EXTENSION, which removes some checks in the hot
> >> path.
> >
> > FWIW, that was my original design but there was some resistance to
> > adding more to the page struct and page extension was suggested
> > instead.
> 
> From looking at both versions, I have to say that having the metadata in
> struct page makes the code easier to understand and removes some special
> cases and bookkeeping.
> 
> > I'm wondering how much performance we're loosing by having to split
> > hugepages. Any chance this can be quantified somehow? Maybe we can
> > have a pool of some sorts reserved for userpages and group allocations
> > so that we can track the XPFO state at the hugepage level instead of
> > at the 4k level to prevent/reduce page splitting. Not sure if that
> > causes issues or has any unwanted side effects though...
> 
> Optimizing the allocation/deallocation path might be worthwhile, because
> that's where most of the overhead goes. I haven't looked into how to do
> this yet. I'd appreciate if someone has pointers to code that tries to
> achieve similar functionality to get me started.
> 
> That being said, I'm wondering whether we have unrealistic expectations
> about the overhead here and whether it's worth turning this patch into
> something far more complicated. Opinions?

I think that implementing Dave Hansen's suggestions of not doing
flushes/other work on every map/unmap, but only when pages are added
to the various free lists will probably help out a lot. That's where I
got stuck last time when I was trying to do it, though :)

Cheers,

Tycho

  reply	other threads:[~2018-09-17 10:19 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-20 21:25 Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs in mind (for KVM to isolate its guests per CPU) Konrad Rzeszutek Wilk
2018-08-20 21:48 ` Linus Torvalds
     [not found]   ` <1534801939.10027.24.camel@amazon.co.uk>
2018-08-20 22:18     ` Kees Cook
2018-08-20 22:27     ` Linus Torvalds
2018-08-20 22:35       ` Tycho Andersen
2018-08-20 22:59         ` Dave Hansen
2018-08-20 23:14           ` David Woodhouse
2018-08-20 23:26             ` Dave Hansen
2018-08-20 23:38               ` Linus Torvalds
2018-08-21  9:57       ` David Woodhouse
2018-08-21 14:01         ` Liran Alon
2018-08-21 14:22           ` David Woodhouse
2018-08-21 23:04             ` Liran Alon
2018-08-30 16:00       ` Julian Stecklina
2018-08-31 15:26         ` Tycho Andersen
2018-09-01 21:38         ` Linus Torvalds
2018-09-03 14:51           ` Julian Stecklina
2018-09-12 15:37             ` Julian Stecklina
2018-09-13  6:11               ` Juerg Haefliger
2018-09-17 10:01                 ` Julian Stecklina
2018-09-17 10:19                   ` Tycho Andersen [this message]
2018-09-17 13:27                   ` Christoph Hellwig
2018-09-14 17:06               ` Khalid Aziz
2018-09-17  9:51                 ` Julian Stecklina
2018-09-18 23:00                   ` Khalid Aziz
2018-09-24 14:45                     ` Stecklina, Julian
2018-10-15  8:07                       ` Khalid Aziz
2018-10-24 11:00                         ` Khalid Aziz
2018-10-24 15:00                           ` Tycho Andersen
2018-09-03 15:26           ` Andi Kleen
2018-09-04  9:37             ` Julian Stecklina
     [not found]           ` <CACfEFw_h5uup-anKZwfBcWMJB7gHxb9NEPTRSUAY0+t11RiQbg@mail.gmail.com>
2018-09-03 15:36             ` Andi Kleen
2018-09-07 21:30         ` Khalid Aziz
2018-08-31  8:43     ` James Bottomley
2018-09-19  1:03     ` Balbir Singh
2018-09-19 15:43       ` Jonathan Adams
2018-09-23  2:33         ` Balbir Singh
2018-09-25 14:12           ` Stecklina, Julian

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