linux-kernel - Re: [PATCH 03/16] x86/entry/32: Leave the kernel via the trampoline stack

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Date:   Fri, 19 Jan 2018 10:57:05 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Brian Gerst <brgerst@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linus Torvalds <torvalds@...ux-foundation.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>,
        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>, Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 03/16] x86/entry/32: Leave the kernel via the trampoline
 stack

On Wed, Jan 17, 2018 at 10:12:32AM -0800, Andy Lutomirski wrote:
> I would optimize for simplicity, not speed.  You're already planning
> to write to CR3, which is serializing, blows away the TLB, *and* takes
> the absurdly large amount of time that the microcode needs to blow
> away the TLB.

Okay, so I am going to do the stack-switch before pt_regs is restored.
This is at least better than playing games with hiding the entry/exit
%esp somewhere in stack-memory.


Thanks,

	Joerg