linux-kernel - Re: [PATCH 09/31] x86/entry/32: Leave the kernel via trampoline stack

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Message-ID: <CA+55aFzB9H=RT6YB3onZCephZMs9ccz4aJ_jcPcfEkKJD_YDCQ@mail.gmail.com>
Date:   Fri, 9 Feb 2018 09:05:02 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 09/31] x86/entry/32: Leave the kernel via trampoline stack

On Fri, Feb 9, 2018 at 1:25 AM, Joerg Roedel <joro@...tes.org> wrote:
> +
> +       /* Copy over the stack-frame */
> +       cld
> +       rep movsb

Ugh. This is going to be horrendous. Maybe not noticeable on modern
CPU's, but the whole 32-bit code is kind of pointless on a modern CPU.

At least use "rep movsl". If the kernel stack isn't 4-byte aligned,
you have issues.

             Linus