Re: [PATCH v2 1/7] KVM: x86/mmu: Track if shadow MMU active

[Paolo Bonzini]

On 29/04/21 23:18, Ben Gardon wrote:
> +void activate_shadow_mmu(struct kvm *kvm)
> +{
> +	kvm->arch.shadow_mmu_active = true;
> +}
> +

I think there's no lock protecting both the write and the read side.
Therefore this should be an smp_store_release, and all checks in
patch 2 should be an smp_load_acquire.

Also, the assignments to slot->arch.rmap in patch 4 (alloc_memslot_rmap)
should be an rcu_assign_pointer, while __gfn_to_rmap must be changed like so:

+	struct kvm_rmap_head *head;
...
-	return &slot->arch.rmap[level - PG_LEVEL_4K][idx];
+	head = srcu_dereference(slot->arch.rmap[level - PG_LEVEL_4K], &kvm->srcu,
+				 lockdep_is_held(&kvm->slots_arch_lock));
+       return &head[idx];

Paolo