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Date: Mon, 20 Aug 2018 16:35:57 -0600
From: Tycho Andersen <>
To: Linus Torvalds <>
Cc: David Woodhouse <>,
	Konrad Rzeszutek Wilk <>,,,
	Jim Mattson <>,
	Andrew Cooper <>,
	Linux Kernel Mailing List <>,
	Boris Ostrovsky <>,
	linux-mm <>, Thomas Gleixner <>,,,
	Andi Kleen <>,
	Khalid Aziz <>,,
	Liran Alon <>, Kees Cook <>,,
	Kernel Hardening <>,, Tyler Hicks <>,
	John Haxby <>, Jon Masters <>
Subject: Re: Redoing eXclusive Page Frame Ownership (XPFO) with isolated CPUs
 in mind (for KVM to isolate its guests per CPU)

On Mon, Aug 20, 2018 at 03:27:52PM -0700, Linus Torvalds wrote:
> On Mon, Aug 20, 2018 at 3:02 PM Woodhouse, David <> wrote:
> >
> > It's the *kernel* we don't want being able to access those pages,
> > because of the multitude of unfixable cache load gadgets.
> Ahh.
> I guess the proof is in the pudding. Did somebody try to forward-port
> that patch set and see what the performance is like?
> It used to be just 500 LOC. Was that because they took horrible
> shortcuts? Are the performance numbers for the 32-bit case that
> already had the kmap() overhead?

The last version I worked on was a bit before Meltdown was public:

The overhead was a lot, but Dave Hansen gave some ideas about how to
speed things up in this thread:

Since meltdown hit, I haven't worked seriously on understand and
implementing his suggestions, in part because it wasn't clear to me
what pieces of the infrastructure we might be able to re-use. Someone
who knows more about mm/ might be able to suggest an approach, though.


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