linux-kernel - Re: [PATCH 1/5] x86/ibrs: Introduce native_rdmsrl, and native

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Date:   Fri, 12 Jan 2018 22:19:57 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     "Raj, Ashok" <ashok.raj@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.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>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>
Subject: Re: [PATCH 1/5] x86/ibrs: Introduce native_rdmsrl, and native_wrmsrl

On Thu, Jan 11, 2018 at 7:01 PM, Raj, Ashok <ashok.raj@...el.com> wrote:
> On Thu, Jan 11, 2018 at 06:20:13PM -0800, Andy Lutomirski wrote:
>> On Thu, Jan 11, 2018 at 5:52 PM, Raj, Ashok <ashok.raj@...el.com> wrote:
>> >>
>> >> What's wrong with native_read_msr()?
>> >
>> > Yes, i think i should have added to msr.h. The names didn't read as a
>> > pair, one was native_read_msr, wrmsrl could be taken over when paravirt is
>> > defined?
>>
>> Why do you need to override paravirt?
>
> The idea was since these MSR's are passed through we shouldn't need to
> handle them any differently. Also its best to do this as soon as possible
> and avoid longer paths to get this barrier to hardware.
>

It should end up with essentially the same instructions at runtime.
I'm generally in favor of using the less weird code when it will work.