Re: [PATCH v2 2/5] x86/idle: Disable IBRS when cpu is offline

[Waiman Long]

On 6/21/23 10:54, Peter Zijlstra wrote:
> On Wed, Jun 21, 2023 at 10:51:33AM -0400, Waiman Long wrote:
> > On 6/21/23 10:48, Peter Zijlstra wrote:
> > > On Wed, Jun 21, 2023 at 10:44:23AM -0400, Waiman Long wrote:
> > >
> > > > Well, hlt_play_dead() is only called if cpuidle_play_dead() returns an error
> > > > which is not the typical case. My testing does confirm that this patch is
> > > > able to keep the IBRS bit off when a CPU is offline via its online sysfs
> > > > file.
> > > The point is; your re-enable IBRS hunk at the end is dead-code. It
> > > should never ever run and having it is confusing.
> > What I meant is that hlt_play_dead() should never be called unless there is
> > some serious problem with the system and native_play_dead() does return in
> > normal usage.
> This is all through arch_cpu_idle_dead() which is __noreturn. And no,
> none of this must ever return.
>
> If you want an offline CPU to come back, you re-init.

Yes, you are right. I thought it will return. I will update the patch 
accordingly.

Thanks,
Longman