KVM: Make kvm_follow_pfn.refcounted_page a required field

Now that the legacy gfn_to_pfn() APIs are gone, and all callers of
hva_to_pfn() pass in a refcounted_page pointer, make it a required field
to ensure all future usage in KVM plays nice.

Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20241010182427.1434605-82-seanjc@google.com>

Author: sean-jc

virt/kvm/kvm_main.c

@@ -2834,8 +2834,7 @@ static kvm_pfn_t kvm_resolve_pfn(struct kvm_follow_pfn *kfp, struct page *page,
 		pfn = page_to_pfn(page);
 	}
 
-	if (kfp->refcounted_page)
-		*kfp->refcounted_page = page;
+	*kfp->refcounted_page = page;
 
 	return pfn;
 }
@@ -2986,6 +2985,9 @@ kvm_pfn_t hva_to_pfn(struct kvm_follow_pfn *kfp)
 
 	might_sleep();
 
+	if (WARN_ON_ONCE(!kfp->refcounted_page))
+		return KVM_PFN_ERR_FAULT;
+
 	if (hva_to_pfn_fast(kfp, &pfn))
 		return pfn;