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

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Message-ID: <CALCETrVSCTO_VBzngZNgiCoRwKZiBa72r9z4_A-R5CAdmqi6Lg@mail.gmail.com>
Date:   Fri, 12 Jan 2018 22:20:51 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Raj, Ashok" <ashok.raj@...el.com>,
        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>,
        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 9:03 PM, Dave Hansen <dave.hansen@...el.com> wrote:
> 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.
>

How could those possibly be any worse than any other indirect call in
the kernel?