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

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Message-ID: <212680b8-6f8d-f785-42fd-61846553570d@intel.com>
Date:   Tue, 12 Dec 2017 12:21:07 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Andy Lutomirsky <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.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 12/12/2017 11:21 AM, Thomas Gleixner wrote:
> The only critical interaction is the return to user path (user CS/SS) and
> we made sure with the LAR touching that these are precached in the CPU
> before we go into fragile exit code.

How do we make sure that it _stays_ cached?

Surely there is weird stuff like WBINVD or SMI's that can come at very
inconvenient times and wipe it out of the cache.