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From: Andy Lutomirski <luto@kernel.org>
Date: Tue, 5 Dec 2017 15:19:08 -0800
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Subject: Re: [patch 00/60] x86/kpti: Kernel Page Table Isolation (was KAISER)
To: Dave Hansen <dave.hansen@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bpetkov@suse.de>,
        Greg KH <gregkh@linuxfoundation.org>, Kees Cook <keescook@google.com>,
        Hugh Dickins <hughd@google.com>, Brian Gerst <brgerst@gmail.com>,
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        Juergen Gross <jgross@suse.com>,
        David Laight <David.Laight@aculab.com>,
        Eduardo Valentin <eduval@amazon.com>, aliguori@amazon.com,
        Will Deacon <will.deacon@arm.com>,
        Daniel Gruss <daniel.gruss@iaik.tugraz.at>
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On Tue, Dec 5, 2017 at 1:57 PM, Dave Hansen <dave.hansen@intel.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.