linux-kernel - Re: Linux 4.15-rc7

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Date:   Fri, 12 Jan 2018 21:41:08 +0100
From:   Pavel Machek <pavel@....cz>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Olivier Galibert <galibert@...ox.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        jikos@...e.cz
Subject: Re: Linux 4.15-rc7

On Fri 2018-01-12 11:44:48, Linus Torvalds wrote:
> On Fri, Jan 12, 2018 at 11:38 AM, Pavel Machek <pavel@....cz> wrote:
> >
> > I'll try to do the right thing. OTOH... I don't like the fact that
> > kernel memory on my machine is currently readable, probably even from
> > javascript.
> 
> Oh, absolutely. I'm just saying that it's probably best to try to
> start from the x86-64 KPTI model, and see how that works for x86-32.
> 
> Maybe some of the 4G:4G entry code could come in handy as a "these are
> the issues" kind of thing.

Ok, so I do have the diff that compiles, and it is 300 lines. Those
will be extremely tricky 300 lines, but...

> > I tried disabling CPU caches. Just like that, off, boom. My system
> > will not survive that, and it looks like 100x slowdown.
> 
> Yeah, no. That is not a realistic thing to do on any hardware since
> the PPro, I'm afraid.

What is special about PPro?

Well -- cache off kind of is what I want -- kills Spectre _and_
Meltdown ;-), attacking close to the fundametal issue. And it really
should be doable on UP system, right?

I guess I should re-try with plain VGA console, not framebuffer.
									
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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