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Date: Sat, 1 Sep 2018 14:38:43 -0700
From: 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 Fri, Aug 31, 2018 at 12:45 AM Julian Stecklina <> wrote:
> I've been spending some cycles on the XPFO patch set this week. For the
> patch set as it was posted for v4.13, the performance overhead of
> compiling a Linux kernel is ~40% on x86_64[1]. The overhead comes almost
> completely from TLB flushing. If we can live with stale TLB entries
> allowing temporary access (which I think is reasonable), we can remove
> all TLB flushing (on x86). This reduces the overhead to 2-3% for
> kernel compile.

I have to say, even 2-3% for a kernel compile sounds absolutely horrendous.

Kernel bullds are 90% user space at least for me, so a 2-3% slowdown
from a kernel is not some small unnoticeable thing.


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