linux-kernel - Re: [PATCH 00/31 v2] PTI support for x86

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Message-ID: <20180209210918.GA7333@amd>
Date:   Fri, 9 Feb 2018 22:09:18 +0100
From:   Pavel Machek <pavel@....cz>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 00/31 v2] PTI support for x86_32

On Fri 2018-02-09 17:47:43, Andy Lutomirski wrote:
> On Fri, Feb 9, 2018 at 9:25 AM, Joerg Roedel <joro@...tes.org> wrote:
> > Hi,
> >
> > here is the second version of my PTI implementation for
> > x86_32, based on tip/x86-pti-for-linus. It took a lot longer
> > than I had hoped, but there have been a number of obstacles
> > on the way. It also isn't the small patch-set anymore that v1
> > was, but compared to it this one actually works :)
> 
> One thing worth noting is that performance of this whole series is
> going to be abysmal due to the complete lack of 32-bit PCID.  Maybe
> any kernel built with this option set that runs on a CPU that has
>the

What kind of slowdown are we talking about here?

> PCID bit set in CPUID should print a big fat warning like "WARNING:
> you are using 32-bit PTI on a 64-bit PCID-capable CPU.  Your
> performance will increase dramatically if you switch to a 64-bit
> kernel."

Hardware supports PCID even on 32-bit kernels, no?

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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