[PATCH v3 3/8] x86, lib: Add WBNOINVD helper functions

[Peter Zijlstra]

On Thu, Jul 10, 2025 at 04:37:29PM +0200, Peter Zijlstra wrote:
> On Thu, Jul 10, 2025 at 01:29:02PM +0200, Borislav Petkov wrote:
> > On Thu, May 22, 2025 at 04:37:27PM -0700, Sean Christopherson wrote:
> > > diff --git a/arch/x86/lib/cache-smp.c b/arch/x86/lib/cache-smp.c
> > > index 079c3f3cd32c..1789db5d8825 100644
> > > --- a/arch/x86/lib/cache-smp.c
> > > +++ b/arch/x86/lib/cache-smp.c
> > > @@ -19,3 +19,14 @@ void wbinvd_on_all_cpus(void)
> > >  	on_each_cpu(__wbinvd, NULL, 1);
> > >  }
> > >  EXPORT_SYMBOL(wbinvd_on_all_cpus);
> > > +
> > > +static void __wbnoinvd(void *dummy)
> > > +{
> > > +	wbnoinvd();
> > > +}
> > > +
> > > +void wbnoinvd_on_all_cpus(void)
> > > +{
> > > +	on_each_cpu(__wbnoinvd, NULL, 1);
> > > +}
> > > +EXPORT_SYMBOL(wbnoinvd_on_all_cpus);
> > 
> > If there's no particular reason for the non-GPL export besides being
> > consistent with the rest - yes, I did the change for wbinvd_on_all_cpus() but
> > that was loooong time ago - I'd simply make this export _GPL.
> 
> Uhhhh, how about we use this fancy export to known modules only thing
> for this?
> 
> These are typical things we do *NOT* want people to actually use.

So kvm-amd is the SEV stuff, AGPGART is the ancient crap nobody cares
about, CCP is more SEV stuff, DRM actually does CLFLUSH loops, but has a
WBINVD fallback. i915 is rude and actually does WBINVD. Could they
pretty please also do CLFLUSH loops?

Anyway, the below seems to survive an allmodconfig.

---
diff --git a/arch/x86/lib/cache-smp.c b/arch/x86/lib/cache-smp.c
index c5c60d07308c..ac3cc32a4054 100644
--- a/arch/x86/lib/cache-smp.c
+++ b/arch/x86/lib/cache-smp.c
@@ -12,19 +12,19 @@ void wbinvd_on_cpu(int cpu)
 {
 	smp_call_function_single(cpu, __wbinvd, NULL, 1);
 }
-EXPORT_SYMBOL(wbinvd_on_cpu);
+EXPORT_SYMBOL_GPL_FOR_MODULES(wbinvd_on_cpu, "kvm-amd,agpgart,ccp,drm,i915");
 
 void wbinvd_on_all_cpus(void)
 {
 	on_each_cpu(__wbinvd, NULL, 1);
 }
-EXPORT_SYMBOL(wbinvd_on_all_cpus);
+EXPORT_SYMBOL_GPL_FOR_MODULES(wbinvd_on_all_cpus, "kvm-amd,agpgart,ccp,drm,i915,intel-gtt");
 
 void wbinvd_on_cpus_mask(struct cpumask *cpus)
 {
 	on_each_cpu_mask(cpus, __wbinvd, NULL, 1);
 }
-EXPORT_SYMBOL_GPL(wbinvd_on_cpus_mask);
+EXPORT_SYMBOL_GPL_FOR_MODULES(wbinvd_on_cpus_mask, "kvm,kvm-amd,agpgart,ccp,drm,i915");
 
 static void __wbnoinvd(void *dummy)
 {
@@ -35,10 +35,10 @@ void wbnoinvd_on_all_cpus(void)
 {
 	on_each_cpu(__wbnoinvd, NULL, 1);
 }
-EXPORT_SYMBOL_GPL(wbnoinvd_on_all_cpus);
+EXPORT_SYMBOL_GPL_FOR_MODULES(wbnoinvd_on_all_cpus, "kvm-amd,agpgart,ccp,drm,i915");
 
 void wbnoinvd_on_cpus_mask(struct cpumask *cpus)
 {
 	on_each_cpu_mask(cpus, __wbnoinvd, NULL, 1);
 }
-EXPORT_SYMBOL_GPL(wbnoinvd_on_cpus_mask);
+EXPORT_SYMBOL_GPL_FOR_MODULES(wbnoinvd_on_cpus_mask, "kvm-amd,agpgart,ccp,drm,i915");