linux-kernel - Re: [PATCH 02/24] x86/traps: Move arch/x86/kernel/traps.c to arch/x86/entry/

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Message-ID: <YTCsWpSmPYvXa1xz@hirez.programming.kicks-ass.net>
Date:   Thu, 2 Sep 2021 12:50:02 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lai Jiangshan <laijs@...ux.alibaba.com>
Cc:     Joerg Roedel <jroedel@...e.de>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Chester Lin <clin@...e.com>, Juergen Gross <jgross@...e.com>,
        andrew.cooper3@...rix.com
Subject: Re: [PATCH 02/24] x86/traps: Move arch/x86/kernel/traps.c to
 arch/x86/entry/

On Thu, Sep 02, 2021 at 05:21:51PM +0800, Lai Jiangshan wrote:
> 
> 
> On 2021/9/2 16:09, Joerg Roedel wrote:
> > On Wed, Sep 01, 2021 at 01:50:03AM +0800, Lai Jiangshan wrote:
> > >   arch/x86/entry/Makefile            | 5 ++++-
> > >   arch/x86/{kernel => entry}/traps.c | 0
> > >   arch/x86/kernel/Makefile           | 5 +----
> > >   3 files changed, 5 insertions(+), 5 deletions(-)
> > >   rename arch/x86/{kernel => entry}/traps.c (100%)
> > 
> >  From looking over the patch-set I didn't spot the reason for putting the
> > entry C code into traps.c. Can you explain that please? Otherwise I'd
> > prefer to create a new file, like arch/x86/entry/entry64.c.
> 
> 
> I agree, and I think Peter is handling it.

I don't think I said that. I said I like the patches but there's a lot
of scary code and details to review, which takes time.

I've now done a second reading of the patches and provided some more
feedback, but I'm very sure I didn't get to the scary details yet.

One thing that got pointed out (by Andrew Cooper) is that by moving the
whole SWAPGS trainwreck to C it becomes entirely 'trivial' to sneak in
an 'accidental' per-cpu reference before having done the SWAPGS dance.

I'm myself not (yet) convinced that's a good enough reason to leave it
in ASM, but it does certainly need consideration.