Re: [PATCH v2 31/50] KVM: x86: Do CPU compatibility checks in x86 code

[Sean Christopherson]

On Mon, Dec 05, 2022, Isaku Yamahata wrote:
> On Wed, Nov 30, 2022 at 11:09:15PM +0000,
> > index 66f16458aa97..3571bc968cf8 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -9277,10 +9277,36 @@ static inline void kvm_ops_update(struct kvm_x86_init_ops *ops)
> >  	kvm_pmu_ops_update(ops->pmu_ops);
> >  }
> >  
> > +struct kvm_cpu_compat_check {
> > +	struct kvm_x86_init_ops *ops;
> > +	int *ret;
> 
> minor nitpick: just int ret. I don't see the necessity of the pointer.
> Anyway overall it looks good to me.

...

> > @@ -9360,6 +9386,14 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
> >  	if (r != 0)
> >  		goto out_mmu_exit;
> >  
> > +	c.ret = &r;
> > +	c.ops = ops;
> > +	for_each_online_cpu(cpu) {
> > +		smp_call_function_single(cpu, kvm_x86_check_cpu_compat, &c, 1);
> > +		if (r < 0)
> 
> Here it can be "c.ret < 0".

No, because the below goto leads to "return r", i.e. "c.ret" needs to be propagated
to "r".  That's why the code does the admittedly funky "int *ret" thing.

FWIW, this gets cleanup in the end.  "struct kvm_cpu_compat_check" goes away and
"&r" is passed directly to kvm_x86_check_cpu_compat.

> > +			goto out_hardware_unsetup;