linux-kernel - Re: [PATCH v3 7/7] x86/vdso: Move out the CPU number store

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Date:   Mon, 18 Jun 2018 15:08:33 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     "Bae, Chang Seok" <chang.seok.bae@...el.com>
Cc:     Andrew Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Metzger, Markus T" <markus.t.metzger@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 7/7] x86/vdso: Move out the CPU number store

On Thu, Jun 7, 2018 at 10:06 AM Chang S. Bae <chang.seok.bae@...el.com> wrote:
>
> The CPU (and node) number will be written, as early enough,
> to the segment limit of per CPU data and TSC_AUX MSR entry.
> The information has been retrieved by vgetcpu in user space
> and will be also loaded from the paranoid entry, when
> FSGSBASE enabled.
>
> Now storing CPU number to the CPU_NUMBER segment limit is
> done during the bootstrap, while MSR TSC_AUX is written
> during each CPU initialization that is still before IST
> setup.
>
> The redundant setting of the segment in entry/vdso/vma.c
> was removed; a substantial code removal. It removes a
> hotplug notifier, makes a facility useful to both the kernel
> and userspace unconditionally available much sooner.
> (Thanks to HPA for suggesting the cleanup)

Couldn't setup_cpu_number_segment()'s contents go in setup_cpu_number()?

--Andy