linux-kernel - Re: [PATCH 4.19 083/100] x86/fpu: Dont export __kernel_fpu

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Date:   Wed, 1 May 2019 13:59:30 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Borislav Petkov <bp@...e.de>, Rik van Riel <riel@...riel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Andy Lutomirski <luto@...nel.org>,
        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 Kr??má?? <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        kvm ML <kvm@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>, x86-ml <x86@...nel.org>
Subject: Re: [PATCH 4.19 083/100] x86/fpu: Dont export
 __kernel_fpu_{begin,end}()

On Tue, Apr 30, 2019 at 01:38:52PM +0200, Greg Kroah-Hartman wrote:
> commit 12209993e98c5fa1855c467f22a24e3d5b8be205 upstream.
> 
> There is one user of __kernel_fpu_begin() and before invoking it,
> it invokes preempt_disable(). So it could invoke kernel_fpu_begin()
> right away. The 32bit version of arch_efi_call_virt_setup() and
> arch_efi_call_virt_teardown() does this already.
> 
> The comment above *kernel_fpu*() claims that before invoking
> __kernel_fpu_begin() preemption should be disabled and that KVM is a
> good example of doing it. Well, KVM doesn't do that since commit
> 
>   f775b13eedee2 ("x86,kvm: move qemu/guest FPU switching out to vcpu_run")
> 
> so it is not an example anymore.
> 
> With EFI gone as the last user of __kernel_fpu_{begin|end}(), both can
> be made static and not exported anymore.

This is just a cleanup and therefore doesn't seem to satisfy the rules
for stable patches per Documentation/process/stable-kernel-rules.rst
("It must fix a real bug that bothers people / fix a problem that causes
a build error").

Why is it being queued up for stable and why are the rules disregarded here?

Thanks,

Lukas