Re: [PATCH v2] x86/kvm: Use RCU for svm_vm_data_hash

[Sean Christopherson <seanjc@google.com>]

KVM: SVM:

"x86/kvm:" is specifically for guest-side code, e.g. arch/x86/kernel/kvm.c

> Changes since v1:

In the future, please wait the "normal" amount of time before sending a new
version, e.g. a day or two for something relatively simple like this.  I.e.
treat feedback from Sashiko like feedback from a human reviewer, and don't spam
patches.

There are times when it's acceptable to break the "don't spam patches" rule, but
this isn't one of those times.

>  int avic_vcpu_precreate(struct kvm *kvm)
> @@ -373,9 +373,12 @@ void avic_vm_pre_destroy(struct kvm *kvm)
>  	if (WARN_ON_ONCE(!enable_apicv) || !kvm_svm->avic_vm_id)
>  		return;
>  
> -	guard(spinlock_irqsave)(&svm_vm_data_hash_lock);
> +	{
> +		guard(spinlock_irqsave)(&svm_vm_data_hash_lock);
> +		hash_del_rcu(&kvm_svm->hnode);

Eww.  Don't open code scoped_guard(), e.g. this should work:

	scoped_guard(spinlock_irqsave, &svm_vm_data_hash_lock)
		hash_del(&kvm_svm->hnode);

	synchronize_rcu();

I'm a little hesitant to put a full synchronize_rcu() in the destroy path, but
in practice it's should be ok.