linux-kernel - Re: [PATCH 3/7] x86/enter: Use IBRS on syscall and interrupts

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Message-ID: <20180104200036.GB30228@kroah.com>
Date:   Thu, 4 Jan 2018 21:00:36 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] x86/enter: Use IBRS on syscall and interrupts

On Thu, Jan 04, 2018 at 09:56:44AM -0800, Tim Chen wrote:
> 
> That is a minor inefficiency only, but we can eliminate it by saving
> the MSR when entering the NMI in save_paranoid and restoring it when
> exiting the NMI.

Any hints as to what exactly "minor" means in cycles here?  :)

thanks,

greg k-h