Re: [PATCH v4 04/19] x86/cea: Export per CPU array 'cea_exception_stacks' for KVM to use

[Xin Li]

On 4/10/2025 7:18 AM, Dave Hansen wrote:
> On 4/10/25 01:53, Christoph Hellwig wrote:
> > On Fri, Mar 28, 2025 at 10:11:50AM -0700, Xin Li (Intel) wrote:
> > > The per CPU array 'cea_exception_stacks' points to per CPU stacks
> > > +/*
> > > + * FRED introduced new fields in the host-state area of the VMCS for
> > > + * stack levels 1->3 (HOST_IA32_FRED_RSP[123]), each respectively
> > > + * corresponding to per CPU stacks for #DB, NMI and #DF.  KVM must
> > > + * populate these each time a vCPU is loaded onto a CPU.
> > > + */
> > > +EXPORT_PER_CPU_SYMBOL(cea_exception_stacks);
> > Exporting data vs accessors for it is usually a bad idea.  Doing a
> > non-_GPl for such a very low level data struture is even worse.
>
> Big ack on this.
>
> I don't even see a single caller of __this_cpu_ist_top_va() that's
> remotely performance sensitive or that needs to be inline.
>
> Just make the __this_cpu_ist_top/bottom_va() macros into real functions
> and export __this_cpu_ist_top_va(). It's going to be a pretty tiny
> function but I think that's tolerable.

Right, that does make sense to me.