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

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Date:   Thu, 11 Jan 2018 21:03:56 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Raj, Ashok" <ashok.raj@...el.com>,
        Andy Lutomirski <luto@...nel.org>
Cc:     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>,
        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 01/11/2018 07:01 PM, Raj, Ashok 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.

We were also worried about the indirect calls that are part of the
paravirt interfaces when retpolines are not in place.