linux-kernel - Re: 32-bit PTI with THP = userspace corruption

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Message-ID: <alpine.LRH.2.21.1809111454100.29433@math.ut.ee>
Date:   Tue, 11 Sep 2018 14:58:10 +0300 (EEST)
From:   Meelis Roos <mroos@...ux.ee>
To:     Joerg Roedel <jroedel@...e.de>
cc:     Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel list <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, Andrea Arcangeli <aarcange@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: 32-bit PTI with THP = userspace corruption

> 	4) Disable PTI support on 2-level paging by making it dependent
> 	   on CONFIG_X86_PAE. This is, imho, the least ugly option
> 	   because the machines that do not support PAE are most likely
> 	   too old to be affected my Meltdown anyway. We might also
> 	   consider switching i386_defconfig to PAE?
> 
> Any other thoughts?

The machines where I have PAE off are the ones that have less memory. 
PAE is off just for performance reasons, not lack of PAE. PAE should be 
present on all of my affected machines anyway and current distributions 
seem to mostly assume 686 and PAE anyway for 32-bit systems.

-- 
Meelis Roos (mroos@...ee)      http://www.cs.ut.ee/~mroos/