linux-kernel - Re: [PATCH] x86/fpu: Remove the _GPL from the kernel_fpu

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Date:   Sun, 5 May 2019 21:09:09 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Rik van Riel <riel@...riel.com>
cc:     Sebastian Gottschall <s.gottschall@...media-net.de>,
        Ingo Molnar <mingo@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Nicolai Stange <nstange@...e.de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        stable@...r.kernel.org, Jiri Kosina <jikos@...os.cz>
Subject: Re: [PATCH] x86/fpu: Remove the _GPL from the kernel_fpu_begin/end()
 export

On Sun, 5 May 2019, Rik van Riel wrote:

> > Using fpu code in kernel space in a kernel module is a derived work of 
> > the kernel itself? dont get me wrong, but this is absurd. i mean you 
> > limit the use of cpu instructions. the use of cpu instructions should 
> > be free of any licensing issue. i would even argument you are 
> > violating the license of the cpu ower given to the kernel by executing 
> > it, by restricting its use for no reason
> 
> Using FPU code in kernel space in a kernel module does not require the 
> use of kernel_fpu_begin/end().
> 
> The kernel module could simply disable preemption, save the FPU 
> registers, use the FPU, restore the FPU registers, and reenable 
> preemption.

That means the module basically reimplemented kernel_fpu_begin/end() in 
its whole (not getting the further optimizations implemented by the 
kernel, sure). And therefore I sort of don't see the point of "hiding" it.

Thanks,

-- 
Jiri Kosina
SUSE Labs