linux-kernel - Re: [patch 00/60] x86/kpti: Kernel Page Table Isolation (was KAISER)

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Message-ID: <CALCETrWJf-O-x6ZRfhfBjM0T6TBeK8LRwrP5SFLdewRVfZPmKQ@mail.gmail.com>
Date:   Tue, 5 Dec 2017 15:19:08 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bpetkov@...e.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>, aliguori@...zon.com,
        Will Deacon <will.deacon@....com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>
Subject: Re: [patch 00/60] x86/kpti: Kernel Page Table Isolation (was KAISER)

On Tue, Dec 5, 2017 at 1:57 PM, Dave Hansen <dave.hansen@...el.com> wrote:
> On 12/05/2017 01:49 PM, Andy Lutomirski wrote:
>> Random thought for the future: KPTI will make it possible to avoid
>> global IPI broadcasts on kernel flushes as we discussed, incorrectly,
>> two years ago at LPC.  This could be nice.
>
> I'm slow.  How?
>


By introducing an (optional) atomic check for need-to-flush on
switches from user CR3 to kernel CR3.