Re: [PATCH v3 1/3] x86/idle: Disable IBRS when cpu is offline

[Waiman Long]

On 6/22/23 01:40, Josh Poimboeuf wrote:
> On Wed, Jun 21, 2023 at 08:36:01PM -0400, Waiman Long wrote:
> > +/*
> > + * naitve_play_dead() is essentially a __noreturn function, but it can't
> > + * be marked as such as the compiler may complain about it.
> > + */
> FWIW, we could in theory do so by marking the smp_ops.play_dead function
> pointer as __noreturn, but it would be tricky to teach objtool how to
> understand that.
I added the comment here because I had taken out the MSR restoration 
code. We can always replace that later on if there is a better way to do 
that.
> >   void native_play_dead(void)
> >   {
> > +	if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS)) {
> > +		this_cpu_write(x86_spec_ctrl_current, 0);
> > +		native_wrmsrl(MSR_IA32_SPEC_CTRL, 0);
> > +	}
> Can update_spec_ctrl() be used instead?

Yes, the code is similar to what has been done in update_spec_ctrl(). 
Using it, however, will require exporting the function either by putting 
it into a public header or making it a global function.

Cheers,
Longman

>