Re: [PATCH] x86/hyperv: Disable preemption while setting reenlightenment vector

Thomas Gleixner
2019-06-13T19:01:38Z

On Wed, 12 Jun 2019, Vitaly Kuznetsov wrote:
> Dmitry Safonov <dima@arista.com> writes:
> > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> > index 1608050e9df9..0bdd79ecbff8 100644
> > --- a/arch/x86/hyperv/hv_init.c
> > +++ b/arch/x86/hyperv/hv_init.c
> > @@ -91,7 +91,7 @@ EXPORT_SYMBOL_GPL(hv_max_vp_index);
> > static int hv_cpu_init(unsigned int cpu)
> > {
> > u64 msr_vp_index;
> > - struct hv_vp_assist_page **hvp = &hv_vp_assist_page[smp_processor_id()];
> > + struct hv_vp_assist_page **hvp = &hv_vp_assist_page[cpu];
> > void **input_arg;
> > struct page *pg;
> >
> > @@ -103,7 +103,7 @@ static int hv_cpu_init(unsigned int cpu)
> >
> > hv_get_vp_index(msr_vp_index);
> >
> > - hv_vp_index[smp_processor_id()] = msr_vp_index;
> > + hv_vp_index[cpu] = msr_vp_index;
> >
> > if (msr_vp_index > hv_max_vp_index)
> > hv_max_vp_index = msr_vp_index;
>
> The above is unrelated cleanup (as cpu == smp_processor_id() for
> CPUHP_AP_ONLINE_DYN callbacks), right? As I'm pretty sure these can'd be
> preempted.

They can be preempted, but they are guaranteed to run on the upcoming CPU,
i.e. smp_processor_id() is allowed even in preemptible context as the task
cannot migrate.

Thanks,

tglx