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Date:   Thu, 2 Sep 2021 12:50:02 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Lai Jiangshan <laijs@linux.alibaba.com>
Cc:     Joerg Roedel <jroedel@suse.de>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Brijesh Singh <brijesh.singh@amd.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Chester Lin <clin@suse.com>, Juergen Gross <jgross@suse.com>,
        andrew.cooper3@citrix.com
Subject: Re: [PATCH 02/24] x86/traps: Move arch/x86/kernel/traps.c to
 arch/x86/entry/
Message-ID: <YTCsWpSmPYvXa1xz@hirez.programming.kicks-ass.net>
References: <20210831175025.27570-1-jiangshanlai@gmail.com>
 <20210831175025.27570-3-jiangshanlai@gmail.com>
 <YTCGov+vvAMvso7q@suse.de>
 <1f327579-e62a-df65-0763-e88243829db3@linux.alibaba.com>
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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.