diff --git a/fs_mgr/fs_mgr.cpp b/fs_mgr/fs_mgr.cpp
index d26f2d519..ba6b9eb14 100644
--- a/fs_mgr/fs_mgr.cpp
+++ b/fs_mgr/fs_mgr.cpp
@@ -1602,6 +1602,14 @@ bool fs_mgr_load_verity_state(int* mode) {
     return true;
 }
 
+std::string fs_mgr_get_verity_device_name(const FstabEntry& entry) {
+    if (entry.mount_point == "/") {
+        // In AVB, the dm device name is vroot instead of system.
+        return entry.fs_mgr_flags.avb ? "vroot" : "system";
+    }
+    return Basename(entry.mount_point);
+}
+
 bool fs_mgr_is_verity_enabled(const FstabEntry& entry) {
     if (!entry.fs_mgr_flags.verify && !entry.fs_mgr_flags.avb) {
         return false;
@@ -1609,14 +1617,7 @@ bool fs_mgr_is_verity_enabled(const FstabEntry& entry) {
 
     DeviceMapper& dm = DeviceMapper::Instance();
 
-    std::string mount_point;
-    if (entry.mount_point == "/") {
-        // In AVB, the dm device name is vroot instead of system.
-        mount_point = entry.fs_mgr_flags.avb ? "vroot" : "system";
-    } else {
-        mount_point = Basename(entry.mount_point);
-    }
-
+    std::string mount_point = fs_mgr_get_verity_device_name(entry);
     if (dm.GetState(mount_point) == DmDeviceState::INVALID) {
         return false;
     }
@@ -1639,6 +1640,27 @@ bool fs_mgr_is_verity_enabled(const FstabEntry& entry) {
     return false;
 }
 
+bool fs_mgr_verity_is_check_at_most_once(const android::fs_mgr::FstabEntry& entry) {
+    if (!entry.fs_mgr_flags.verify && !entry.fs_mgr_flags.avb) {
+        return false;
+    }
+
+    DeviceMapper& dm = DeviceMapper::Instance();
+    std::string device = fs_mgr_get_verity_device_name(entry);
+
+    std::vector<DeviceMapper::TargetInfo> table;
+    if (dm.GetState(device) == DmDeviceState::INVALID || !dm.GetTableInfo(device, &table)) {
+        return false;
+    }
+    for (const auto& target : table) {
+        if (strcmp(target.spec.target_type, "verity") == 0 &&
+            target.data.find("check_at_most_once") != std::string::npos) {
+            return true;
+        }
+    }
+    return false;
+}
+
 std::string fs_mgr_get_super_partition_name(int slot) {
     // Devices upgrading to dynamic partitions are allowed to specify a super
     // partition name, assumed to be A/B (non-A/B retrofit is not supported).
diff --git a/fs_mgr/include/fs_mgr.h b/fs_mgr/include/fs_mgr.h
index a3bb85215..8abe609a5 100644
--- a/fs_mgr/include/fs_mgr.h
+++ b/fs_mgr/include/fs_mgr.h
@@ -77,6 +77,10 @@ bool fs_mgr_is_verity_enabled(const android::fs_mgr::FstabEntry& entry);
 bool fs_mgr_swapon_all(const android::fs_mgr::Fstab& fstab);
 bool fs_mgr_update_logical_partition(android::fs_mgr::FstabEntry* entry);
 
+// Returns true if the given fstab entry has verity enabled, *and* the verity
+// device is in "check_at_most_once" mode.
+bool fs_mgr_verity_is_check_at_most_once(const android::fs_mgr::FstabEntry& entry);
+
 int fs_mgr_do_format(const android::fs_mgr::FstabEntry& entry, bool reserve_footer);
 
 #define FS_MGR_SETUP_VERITY_SKIPPED  (-3)
diff --git a/fs_mgr/tools/dmctl.cpp b/fs_mgr/tools/dmctl.cpp
index 63661f0aa..9309aadf8 100644
--- a/fs_mgr/tools/dmctl.cpp
+++ b/fs_mgr/tools/dmctl.cpp
@@ -316,7 +316,7 @@ static int TableCmdHandler(int argc, char** argv) {
 
     DeviceMapper& dm = DeviceMapper::Instance();
     std::vector<DeviceMapper::TargetInfo> table;
-    if (!dm.GetTableStatus(argv[0], &table)) {
+    if (!dm.GetTableInfo(argv[0], &table)) {
         std::cerr << "Could not query table status of device \"" << argv[0] << "\"." << std::endl;
         return -EINVAL;
     }
diff --git a/init/first_stage_mount.cpp b/init/first_stage_mount.cpp
index 4b0f05d4a..d458924a7 100644
--- a/init/first_stage_mount.cpp
+++ b/init/first_stage_mount.cpp
@@ -78,6 +78,7 @@ class FirstStageMount {
     ListenerAction HandleBlockDevice(const std::string& name, const Uevent&);
     bool InitRequiredDevices();
     bool InitMappedDevice(const std::string& verity_device);
+    bool InitDeviceMapper();
     bool CreateLogicalPartitions();
     bool MountPartition(const Fstab::iterator& begin, bool erase_used_fstab_entry,
                         Fstab::iterator* end = nullptr);
@@ -97,6 +98,7 @@ class FirstStageMount {
     virtual bool SetUpDmVerity(FstabEntry* fstab_entry) = 0;
 
     bool need_dm_verity_;
+    bool gsi_not_on_userdata_ = false;
 
     Fstab fstab_;
     std::string lp_metadata_partition_;
@@ -267,8 +269,6 @@ bool FirstStageMount::GetDmLinearMetadataDevice() {
     }
 
     required_devices_partition_names_.emplace(super_partition_name_);
-    // When booting from live GSI images, userdata is the super device.
-    required_devices_partition_names_.emplace("userdata");
     return true;
 }
 
@@ -281,25 +281,7 @@ bool FirstStageMount::InitRequiredDevices() {
     }
 
     if (IsDmLinearEnabled() || need_dm_verity_) {
-        const std::string dm_path = "/devices/virtual/misc/device-mapper";
-        bool found = false;
-        auto dm_callback = [this, &dm_path, &found](const Uevent& uevent) {
-            if (uevent.path == dm_path) {
-                device_handler_->HandleUevent(uevent);
-                found = true;
-                return ListenerAction::kStop;
-            }
-            return ListenerAction::kContinue;
-        };
-        uevent_listener_.RegenerateUeventsForPath("/sys" + dm_path, dm_callback);
-        if (!found) {
-            LOG(INFO) << "device-mapper device not found in /sys, waiting for its uevent";
-            Timer t;
-            uevent_listener_.Poll(dm_callback, 10s);
-            LOG(INFO) << "Wait for device-mapper returned after " << t;
-        }
-        if (!found) {
-            LOG(ERROR) << "device-mapper device not found after polling timeout";
+        if (!InitDeviceMapper()) {
             return false;
         }
     }
@@ -327,11 +309,36 @@ bool FirstStageMount::InitRequiredDevices() {
     return true;
 }
 
+bool FirstStageMount::InitDeviceMapper() {
+    const std::string dm_path = "/devices/virtual/misc/device-mapper";
+    bool found = false;
+    auto dm_callback = [this, &dm_path, &found](const Uevent& uevent) {
+        if (uevent.path == dm_path) {
+            device_handler_->HandleUevent(uevent);
+            found = true;
+            return ListenerAction::kStop;
+        }
+        return ListenerAction::kContinue;
+    };
+    uevent_listener_.RegenerateUeventsForPath("/sys" + dm_path, dm_callback);
+    if (!found) {
+        LOG(INFO) << "device-mapper device not found in /sys, waiting for its uevent";
+        Timer t;
+        uevent_listener_.Poll(dm_callback, 10s);
+        LOG(INFO) << "Wait for device-mapper returned after " << t;
+    }
+    if (!found) {
+        LOG(ERROR) << "device-mapper device not found after polling timeout";
+        return false;
+    }
+    return true;
+}
+
 bool FirstStageMount::InitDmLinearBackingDevices(const android::fs_mgr::LpMetadata& metadata) {
     auto partition_names = android::fs_mgr::GetBlockDevicePartitionNames(metadata);
     for (const auto& partition_name : partition_names) {
-        const auto super_device = android::fs_mgr::GetMetadataSuperBlockDevice(metadata);
-        if (partition_name == android::fs_mgr::GetBlockDevicePartitionName(*super_device)) {
+        // The super partition was found in the earlier pass.
+        if (partition_name == super_partition_name_) {
             continue;
         }
         required_devices_partition_names_.emplace(partition_name);
@@ -499,6 +506,10 @@ bool FirstStageMount::TrySwitchSystemAsRoot() {
     if (system_partition == fstab_.end()) return true;
 
     if (MountPartition(system_partition, false)) {
+        if (gsi_not_on_userdata_ && fs_mgr_verity_is_check_at_most_once(*system_partition)) {
+            LOG(ERROR) << "check_most_at_once forbidden on external media";
+            return false;
+        }
         SwitchRoot("/system");
     } else {
         PLOG(ERROR) << "Failed to mount /system";
@@ -612,7 +623,29 @@ void FirstStageMount::UseGsiIfPresent() {
         return;
     }
 
-    if (!android::fs_mgr::CreateLogicalPartitions(*metadata.get(), "/dev/block/by-name/userdata")) {
+    if (!InitDmLinearBackingDevices(*metadata.get())) {
+        return;
+    }
+
+    // Device-mapper might not be ready if the device doesn't use DAP or verity
+    // (for example, hikey).
+    if (access("/dev/device-mapper", F_OK) && !InitDeviceMapper()) {
+        return;
+    }
+
+    // Find the name of the super partition for the GSI. It will either be
+    // "userdata", or a block device such as an sdcard. There are no by-name
+    // partitions other than userdata that we support installing GSIs to.
+    auto super = GetMetadataSuperBlockDevice(*metadata.get());
+    std::string super_name = android::fs_mgr::GetBlockDevicePartitionName(*super);
+    std::string super_path;
+    if (super_name == "userdata") {
+        super_path = "/dev/block/by-name/" + super_name;
+    } else {
+        super_path = "/dev/block/" + super_name;
+    }
+
+    if (!android::fs_mgr::CreateLogicalPartitions(*metadata.get(), super_path)) {
         LOG(ERROR) << "GSI partition layout could not be instantiated";
         return;
     }
@@ -630,6 +663,7 @@ void FirstStageMount::UseGsiIfPresent() {
         fstab_.erase(system_partition);
     }
     fstab_.emplace_back(BuildGsiSystemFstabEntry());
+    gsi_not_on_userdata_ = (super_name != "userdata");
 }
 
 bool FirstStageMountVBootV1::GetDmVerityDevices() {