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Re: [PATCH 1/5] x86/ibrs: Introduce native_rdmsrl, and native_wrmsrl




On Thu, 2018-01-11 at 21:03 -0800, Dave Hansen 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@xxxxxxxxx> 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.

I have repeatedly been told that these go away, and are converted to
direct branches by the time the kernel is running userspace.

I suppose I really ought to validate that with qemu -d in_asm or
something. I couldn't see it in the code... but I haven't looked that
hard yet.

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