linux-kernel - Re: [patch 13/16] x86/ldt: Introduce LDT write fault handler

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Message-ID: <20171212222516.kt4xp4ec2weavbsz@hirez.programming.kicks-ass.net>
Date:   Tue, 12 Dec 2017 23:25:16 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Andy Lutomirsky <luto@...nel.org>,
        Borislav Petkov <bpetkov@...e.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Will Deacon <will.deacon@....com>,
        linux-mm <linux-mm@...ck.org>
Subject: Re: [patch 13/16] x86/ldt: Introduce LDT write fault handler

On Tue, Dec 12, 2017 at 10:41:03PM +0100, Thomas Gleixner wrote:
> Now that made me go back to the state of the patch series which made us
> make that magic 'touch' and write fault handler. The difference to the code
> today is that it did not prepopulate the user visible mapping.
> 
> We added that later because we were worried about not being able to
> populate it in the #PF due to memory pressure without ripping out the magic
> cure again.
> 
> But I did now and actually removing both the user exit magic 'touch' code
> and the write fault handler keeps it working.

Argh, had we really not tried that!? Bah.