Re: [PATCH 3/5] x86/ibrs: Add direct access support for MSR_IA32_SPEC_CTRL

[Peter Zijlstra]

On Thu, Jan 11, 2018 at 05:58:11PM -0800, Dave Hansen wrote:
> On 01/11/2018 05:32 PM, Ashok Raj wrote:
> > +static void save_guest_spec_ctrl(struct vcpu_vmx *vmx)
> > +{
> > +	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL)) {
> > +		vmx->spec_ctrl = spec_ctrl_get();
> > +		spec_ctrl_restriction_on();
> > +	} else
> > +		rmb();
> > +}
> 
> Does this need to be "ifence()"?  Better yet, do we just need to create
> a helper for boot_cpu_has(X86_FEATURE_SPEC_CTRL) that does the barrier?

static_cpu_has() + hard asm-goto requirement. Please drop all the above
nonsense on the floor hard.

Let backporters sort out whever they need, don't introduce crap like
that upstream.