Re: [PATCH v2 4/8] x86/spec_ctrl: Add sysctl knobs to enable/disable SPEC_CTRL feature

[Thomas Gleixner]

On Sat, 6 Jan 2018, Dave Hansen wrote:

> On 01/06/2018 09:41 AM, Van De Ven, Arjan wrote:
> >>>>  .macro DISABLE_IBRS
> >>>> -	ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_SPEC_CTRL
> >>>> +	testl	$1, dynamic_ibrs
> >>> On every system call we end up hammering on this 'dynamic_ibrs'
> >>> variable. And it looks like it can be flipped via the IPI mechanism.
> >>>
> >>> Would it make sense for this to be per-cpu?
> >>
> >> It's probably better to either just make it __read_mostly or get the
> >> static branches that folks were suggesting actually working.
> > 
> > I still wonder if this isn't just better as a boot command line
> 
> It's simpler that way.  But, ideally, we want to make it runtime
> switchable to match the implementation in the distros.

Stop this silly argument please. The distros shipped lots of crap which we
dont want to have at all.

I told you folks yesterday what I want to see and the sysctl thing is the
least on that list and it's not needed for getting the important thing -
the protection - to work.

Can we pretty please do the basics and worry about that sysctl or whatever
people have on their wishlist once the dust settled.

Thanks,

	tglx