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Date: Mon, 20 Aug 2018 15:59:54 -0700
From: Dave Hansen <>
To: Tycho Andersen <>,
 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 08/20/2018 03:35 PM, Tycho Andersen wrote:
> 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

Unfortunately, I'm not sure there's much of KPTI we can reuse.  KPTI
still has a very static kernel map (well, two static kernel maps) and
XPFO really needs a much more dynamic map.

We do have a bit of infrastructure now to do TLB flushes near the kernel
exit point, but it's entirely for the user address space, which isn't
affected by XPFO.

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