linux-kernel - Re: x86/fpu: Don't export __kernel_fpu

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Date:   Wed, 9 Jan 2019 13:40:14 -0400
From:   Marc Dionne <marc.c.dionne@...il.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        x86@...nel.org
Subject: Re: x86/fpu: Don't export __kernel_fpu_{begin,end}()

On Wed, Jan 9, 2019 at 1:09 PM Sebastian Andrzej Siewior
<bigeasy@...utronix.de> wrote:
>
> On 2019-01-09 17:52:35 [+0100], Greg Kroah-Hartman wrote:
> > If there are no in-kernel users, the symbols should not be exported
> > anymore.  That's nothing new, we have always done this.
>
> The thing is that we had
>   EXPORT_SYMBOL(__kernel_fpu_begin)
>   EXPORT_SYMBOL_GPL(kernel_fpu_begin)
>
> and now __kernel_fpu_begin() is no longer exported and static only.
> All in kernel user (including the kvm module) use kernel_fpu_begin()
> which is not available to proprietary modules. Hence Marc's mail.
>
> > > On the other hand could we just drop EXPORT_SYMBOL_GPL? I doubt this
> > > helps in any way yet please correct me if I am wrong.
> >
> > Yes, it helps, please leave it as-is.
>
> As you say. I only notice that certain things used to work and then no
> longer do because due to $rework it somehow become EXPORT_SYMBOL_GPL
> only and people complain and we tend to switch the export back to
> EXPORT_SYMBOL. I'm not aware of a case where it actually helped in
> anyway.
>
> > thanks,
> >
> > greg k-h
>
> Sebastian

I would point out that there are several precedents for restoring
exports after functionality has been unintentionally made GPL only;
from a quick lookup these are some examples:

  8af190958059 ("x86/paravirt: Remove GPL from pv_ops export")
  31c5bda3a656 ("mm: fix exports that inadvertently make put_page()
EXPORT_SYMBOL_GPL")
  1e5476815fd7 ("x86/tlb: Drop the _GPL from the cpu_tlbstate export")
  b562c171cf01 ("locking/refcounts: Do not force refcount_t usage as
GPL-only export")

Marc