ANDROID: KVM: arm64: Introduce gfn_to_memslot_prot()

Returns the memslot and whether it's writable without requiring a
userspace address at the host.

The userspace address isn't needed to get this information.
Future patches, where the userspace address might not be known,
would need access to the memslot and whether it's writeable.

No functional change intended.

Bug: 357781595
Change-Id: I490c6d41b19825e0a8d05e3a5af660ce31a894d4
Signed-off-by: Fuad Tabba <tabba@google.com>

include/linux/kvm_host.h

@@ -1305,6 +1305,7 @@ int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
 
 int kvm_clear_guest(struct kvm *kvm, gpa_t gpa, unsigned long len);
 struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn);
+struct kvm_memory_slot *gfn_to_memslot_prot(struct kvm *kvm, gfn_t gfn, bool *writable);
 bool kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn);
 bool kvm_vcpu_is_visible_gfn(struct kvm_vcpu *vcpu, gfn_t gfn);
 unsigned long kvm_host_page_size(struct kvm_vcpu *vcpu, gfn_t gfn);

virt/kvm/kvm_main.c

@@ -2673,6 +2673,28 @@ static bool memslot_is_readonly(const struct kvm_memory_slot *slot)
 	return slot->flags & KVM_MEM_READONLY;
 }
 
+/*
+ * Return the memslot of a @gfn and the R/W attribute if slot is valid, or NULL
+ * if slot is not valid.
+ *
+ * @slot: the kvm_memory_slot which contains @gfn
+ * @gfn: the gfn to be translated
+ * @writable: used to return the read/write attribute of the @slot if the hva
+ * is valid and @writable is not NULL
+ */
+struct kvm_memory_slot *gfn_to_memslot_prot(struct kvm *kvm, gfn_t gfn, bool *writable)
+{
+	struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
+
+	if (!slot || slot->flags & KVM_MEMSLOT_INVALID)
+		return NULL;
+
+	if (writable)
+		*writable = !memslot_is_readonly(slot);
+
+	return slot;
+}
+
 static unsigned long __gfn_to_hva_many(const struct kvm_memory_slot *slot, gfn_t gfn,
 				       gfn_t *nr_pages, bool write)
 {