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

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Message-ID: <CA+55aFzo3b2aChbJ2aOSvKbguYKMG8wv02NS8qzp6w2T5z8WTg@mail.gmail.com>
Date:   Tue, 11 Sep 2018 08:20:33 -1000
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Joerg Roedel <jroedel@...e.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>, Meelis Roos <mroos@...ux.ee>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: 32-bit PTI with THP = userspace corruption

On Tue, Sep 11, 2018 at 1:49 AM Joerg Roedel <jroedel@...e.de> wrote:
>
> I had a look into the THP and the HugeTLBfs code, and that is not
> really easy to fix there. As I can see it now, there are a few options
> to fix that, but most of them are ugly:

Just do (4): disable PTI with PAE.

Then we can try to make people perhaps not use !PAE very much, and
warn if you have PAE disabled on a machine that supports it.

As you say, there shouldn't be much of a performance impact from PAE.
There is a more noticeable performance impact from HIGHMEM, not from
HIGHMEM_64G, iirc.

                Linus