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From: Andy Lutomirski <luto@kernel.org>
Date: Fri, 12 Jan 2018 22:20:51 -0800
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Subject: Re: [PATCH 1/5] x86/ibrs: Introduce native_rdmsrl, and native_wrmsrl
To: Dave Hansen <dave.hansen@intel.com>
Cc: "Raj, Ashok" <ashok.raj@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@intel.com>,
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        Paolo Bonzini <pbonzini@redhat.com>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>
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On Thu, Jan 11, 2018 at 9:03 PM, Dave Hansen <dave.hansen@intel.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@intel.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?