ANDROID: KVM: arm64: Implement do_donate() helper for donating memory

Transferring ownership information of a memory region from one component
to another can be achieved using a "donate" operation, which results
in the previous owner losing access to the underlying pages entirely.

Implement a do_donate() helper, along the same lines as do_{un,}share,
to provide this functionality for the host-to-hyp case.

Signed-off-by: Quentin Perret <qperret@google.com>
Bug: 209580772
Change-Id: I426f8b068450e7e6b93ba05a0aea6ce8f93e6bf7
Signed-off-by: Will Deacon <willdeacon@google.com>

arch/arm64/kvm/hyp/nvhe/mem_protect.c

@@ -27,6 +27,7 @@ struct host_kvm host_kvm;
 
 static struct hyp_pool host_s2_pool;
 
+const u8 pkvm_host_id = 0;
 const u8 pkvm_hyp_id = 1;
 
 static void host_lock_component(void)
@@ -469,6 +470,23 @@ struct pkvm_mem_share {
 	const enum kvm_pgtable_prot		completer_prot;
 };
 
+struct pkvm_mem_donation {
+	const struct pkvm_mem_transition	tx;
+};
+
+static u8 completer_owner_id(const struct pkvm_mem_transition *tx)
+{
+	switch (tx->completer.id) {
+	case PKVM_ID_HOST:
+		return pkvm_host_id;
+	case PKVM_ID_HYP:
+		return pkvm_hyp_id;
+	default:
+		WARN_ON(1);
+		return -1;
+	}
+}
+
 struct check_walk_data {
 	enum pkvm_page_state	desired;
 	enum pkvm_page_state	(*get_page_state)(kvm_pte_t pte);
@@ -568,6 +586,16 @@ static int host_initiate_unshare(u64 *completer_addr,
 	return __host_set_page_state_range(addr, size, PKVM_PAGE_OWNED);
 }
 
+static int host_initiate_donation(u64 *completer_addr,
+				  const struct pkvm_mem_transition *tx)
+{
+	u8 owner_id = completer_owner_id(tx);
+	u64 size = tx->nr_pages * PAGE_SIZE;
+
+	*completer_addr = tx->initiator.host.completer_addr;
+	return host_stage2_set_owner_locked(tx->initiator.addr, size, owner_id);
+}
+
 static enum pkvm_page_state hyp_get_page_state(kvm_pte_t pte)
 {
 	if (!kvm_pte_valid(pte))
@@ -619,6 +647,16 @@ static int hyp_ack_unshare(u64 addr, const struct pkvm_mem_transition *tx)
 					    PKVM_PAGE_SHARED_BORROWED);
 }
 
+static int hyp_ack_donation(u64 addr, const struct pkvm_mem_transition *tx)
+{
+	u64 size = tx->nr_pages * PAGE_SIZE;
+
+	if (__hyp_ack_skip_pgtable_check(tx))
+		return 0;
+
+	return __hyp_check_page_state_range(addr, size, PKVM_NOPAGE);
+}
+
 static int hyp_complete_share(u64 addr, const struct pkvm_mem_transition *tx,
 			      enum kvm_pgtable_prot perms)
 {
@@ -637,6 +675,15 @@ static int hyp_complete_unshare(u64 addr, const struct pkvm_mem_transition *tx)
 	return (ret != size) ? -EFAULT : 0;
 }
 
+static int hyp_complete_donation(u64 addr,
+				 const struct pkvm_mem_transition *tx)
+{
+	void *start = (void *)addr, *end = start + (tx->nr_pages * PAGE_SIZE);
+	enum kvm_pgtable_prot prot = pkvm_mkstate(PAGE_HYP, PKVM_PAGE_OWNED);
+
+	return pkvm_create_mappings_locked(start, end, prot);
+}
+
 static int check_share(struct pkvm_mem_share *share)
 {
 	const struct pkvm_mem_transition *tx = &share->tx;
@@ -789,6 +836,82 @@ static int do_unshare(struct pkvm_mem_share *share)
 	return WARN_ON(__do_unshare(share));
 }
 
+static int check_donation(struct pkvm_mem_donation *donation)
+{
+	const struct pkvm_mem_transition *tx = &donation->tx;
+	u64 completer_addr;
+	int ret;
+
+	switch (tx->initiator.id) {
+	case PKVM_ID_HOST:
+		ret = host_request_owned_transition(&completer_addr, tx);
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	if (ret)
+		return ret;
+
+	switch (tx->completer.id){
+	case PKVM_ID_HYP:
+		ret = hyp_ack_donation(completer_addr, tx);
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	return ret;
+}
+
+static int __do_donate(struct pkvm_mem_donation *donation)
+{
+	const struct pkvm_mem_transition *tx = &donation->tx;
+	u64 completer_addr;
+	int ret;
+
+	switch (tx->initiator.id) {
+	case PKVM_ID_HOST:
+		ret = host_initiate_donation(&completer_addr, tx);
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	if (ret)
+		return ret;
+
+	switch (tx->completer.id){
+	case PKVM_ID_HYP:
+		ret = hyp_complete_donation(completer_addr, tx);
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	return ret;
+}
+
+/*
+ * do_donate():
+ *
+ * The page owner transfers ownership to another component, losing access
+ * as a consequence.
+ *
+ * Initiator: OWNED	=> NOPAGE
+ * Completer: NOPAGE	=> OWNED
+ */
+static int do_donate(struct pkvm_mem_donation *donation)
+{
+	int ret;
+
+	ret = check_donation(donation);
+	if (ret)
+		return ret;
+
+	return WARN_ON(__do_donate(donation));
+}
+
 int __pkvm_host_share_hyp(u64 pfn)
 {
 	int ret;