Re: [PATCH v2 1/6] x86/irq: Add enumeration of NMI source reporting CPU feature

[Xin Li]

On 6/11/2024 7:50 PM, H. Peter Anvin wrote:
> On June 11, 2024 7:32:54 PM PDT, Xin Li <xin@xxxxxxxxx> wrote:
> > On 6/11/2024 9:54 AM, Jacob Pan wrote:
> > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > > index 1d7122a1883e..b8b15f20b94e 100644
> > > --- a/arch/x86/Kconfig
> > > +++ b/arch/x86/Kconfig
> > > @@ -511,12 +511,21 @@ config X86_CPU_RESCTRL
> > >    config X86_FRED
> > >    	bool "Flexible Return and Event Delivery"
> > >    	depends on X86_64
> > > +	select X86_NMI_SOURCE
> > >    	help
> > >    	  When enabled, try to use Flexible Return and Event Delivery
> > >    	  instead of the legacy SYSCALL/SYSENTER/IDT architecture for
> > >    	  ring transitions and exception/interrupt handling if the
> > >    	  system supports it.
> > >    +config X86_NMI_SOURCE
> >
> > Lets reuse X86_FRED instead of adding another hard config option. See
> > below.

<snip>

> > With this, no need to add DISABLE_NMI_SOURCE to disabled-features.h:
> >
> > 1) If FRED is not available, NMI source won't be too.
> > 2) If FRED is available but not enabled, all features relying on FRED
> > should be cleared. We probably should move the feature bits clearing
> > code into a static function when more such features are added in future.
> >
> > >      	/* Init cpu_entry_area before IST entries are set up */
> > >    	setup_cpu_entry_areas();
> >
> > Thanks!
> >     Xin
>
> And even if we did, FRED should not *select* NMI_SOURCE; the dependency goes the other way.

Right, I was a bit of confused but was focusing on why do we need this.