From: Pavel Machek <pavel@ucw.cz>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Olivier Galibert <galibert@pobox.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
jikos@suse.cz
Subject: Re: Linux 4.15-rc7
Date: Fri, 12 Jan 2018 15:43:32 +0100 [thread overview]
Message-ID: <20180112144332.GA28083@amd> (raw)
In-Reply-To: <CAK8P3a3xs2-4VXKWum7cXrwUqK7Ysz3HOcikb53qQde2R6Ui4w@mail.gmail.com>
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Hi!
> >> Wasn't/Isn't the 4G/4G memory layout for 32 bits essentially KPTI?
> >
> > Good point. Is that still supported? Was it ever?
> >
> > Umm. I seem to recall that 4G/4G layout was out of tree but never
> > merged.
>
> I think that's correct: it was in RHEL3 and RHEL4 but never merged
> upstream.
Too bad.
> However, there is an important difference between KPTI and X86_4G:
> The former unmaps the kernel pages from the user space page tables,
> but keeps both the linear mapping and the user pages visible in
> kernel mode, while the latter must have also unmapped user space
> pages from kernel mode, requiring a more expensive get_user/put_user
> implementation.
>
> Kees mentioned an idea to also unmap user pages from kernel
> mode as an additional safeguard on top of KPTI, which would get
> it even closer to the X86_4G implementation:
> https://outflux.net/blog/archives/2018/01/04/smep-emulation-in-pti/
Well, I guess at this point I'm looking for a good place to start from...
> Could you be more specific which 32-bit x86 chips you have that are
> affected by Meltdown? Do you mean pre-2004 Pentiums or Core-Duo
> laptops? I would guess that Cyrix/Natsemi/AMD 6x86/MediaGX/Geode
> and AMD NexGen K6/K7 also affected by Spectre but probably not
> Meltdown, and most other 32-bit microarchitectures seem to be purely
> in-order.
I do have Core Solo here'd like to keep working (and useful for web
browsing). Then there's Pentium M. Occasionaly I run 32-bit kernels on
modern machines for testing.
Thanks,
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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next prev parent reply other threads:[~2018-01-12 14:43 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-07 22:55 Linux 4.15-rc7 Linus Torvalds
2018-01-08 7:20 ` Thomas Gleixner
2018-01-10 23:32 ` Pavel Machek
2018-01-11 11:29 ` Olivier Galibert
2018-01-11 14:06 ` Nikolay Borisov
2018-01-12 11:06 ` Pavel Machek
2018-01-12 13:23 ` Arnd Bergmann
2018-01-12 14:43 ` Pavel Machek [this message]
2018-01-12 17:20 ` vcaputo
2018-01-12 20:11 ` Arnd Bergmann
2018-01-12 22:04 ` vcaputo
2018-01-12 22:08 ` Arnd Bergmann
2018-01-12 22:58 ` vcaputo
2018-01-12 17:34 ` Linus Torvalds
2018-01-12 19:38 ` Pavel Machek
2018-01-12 19:44 ` Linus Torvalds
2018-01-12 20:41 ` Pavel Machek
2018-01-13 12:52 ` kernel page table isolation for x86-32 was " Pavel Machek
2018-01-11 14:07 ` Jiri Kosina
2018-01-19 10:28 ` Pavel Machek
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