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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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