diff --git a/core/Makefile b/core/Makefile
index 09f9eb0..da961f2 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -144,6 +144,21 @@
 endif
 FINAL_VENDOR_DEFAULT_PROPERTIES += \
     $(call collapse-pairs, $(PRODUCT_DEFAULT_PROPERTY_OVERRIDES))
+
+# Although these variables are prefixed with TARGET_RECOVERY_, they are also needed under charger
+# mode (via libminui).
+ifdef TARGET_RECOVERY_DEFAULT_ROTATION
+FINAL_VENDOR_DEFAULT_PROPERTIES += \
+    ro.minui.default_rotation=$(TARGET_RECOVERY_DEFAULT_ROTATION)
+endif
+ifdef TARGET_RECOVERY_OVERSCAN_PERCENT
+FINAL_VENDOR_DEFAULT_PROPERTIES += \
+    ro.minui.overscan_percent=$(TARGET_RECOVERY_OVERSCAN_PERCENT)
+endif
+ifdef TARGET_RECOVERY_PIXEL_FORMAT
+FINAL_VENDOR_DEFAULT_PROPERTIES += \
+    ro.minui.pixel_format=$(TARGET_RECOVERY_PIXEL_FORMAT)
+endif
 FINAL_VENDOR_DEFAULT_PROPERTIES := $(call uniq-pairs-by-first-component, \
     $(FINAL_VENDOR_DEFAULT_PROPERTIES),=)
 
@@ -1557,9 +1572,6 @@
 INSTALLED_RECOVERY_BUILD_PROP_TARGET := $(TARGET_RECOVERY_ROOT_OUT)/prop.default
 
 $(INSTALLED_RECOVERY_BUILD_PROP_TARGET): PRIVATE_RECOVERY_UI_PROPERTIES := \
-    TARGET_RECOVERY_DEFAULT_ROTATION:default_rotation \
-    TARGET_RECOVERY_OVERSCAN_PERCENT:overscan_percent \
-    TARGET_RECOVERY_PIXEL_FORMAT:pixel_format \
     TARGET_RECOVERY_UI_ANIMATION_FPS:animation_fps \
     TARGET_RECOVERY_UI_MARGIN_HEIGHT:margin_height \
     TARGET_RECOVERY_UI_MARGIN_WIDTH:margin_width \
@@ -2645,6 +2657,15 @@
 BOARD_AVB_KEY_PATH := external/avb/test/data/testkey_rsa4096.pem
 endif
 
+INTERNAL_AVB_PARTITIONS_IN_CHAINED_VBMETA_IMAGES := \
+    $(BOARD_AVB_VBMETA_MAINLINE) \
+    $(BOARD_AVB_VBMETA_VENDOR)
+
+# Not allowing the same partition to appear in multiple groups.
+ifneq ($(words $(sort $(INTERNAL_AVB_PARTITIONS_IN_CHAINED_VBMETA_IMAGES))),$(words $(INTERNAL_AVB_PARTITIONS_IN_CHAINED_VBMETA_IMAGES)))
+  $(error BOARD_AVB_VBMETA_MAINLINE and BOARD_AVB_VBMETA_VENDOR cannot have duplicates)
+endif
+
 BOOT_FOOTER_ARGS := BOARD_AVB_BOOT_ADD_HASH_FOOTER_ARGS
 DTBO_FOOTER_ARGS := BOARD_AVB_DTBO_ADD_HASH_FOOTER_ARGS
 SYSTEM_FOOTER_ARGS := BOARD_AVB_SYSTEM_ADD_HASHTREE_FOOTER_ARGS
@@ -2655,7 +2676,7 @@
 ODM_FOOTER_ARGS := BOARD_AVB_ODM_ADD_HASHTREE_FOOTER_ARGS
 
 # Helper function that checks and sets required build variables for an AVB chained partition.
-# $(1): the partition to enable AVB chain, e.g., boot or system.
+# $(1): the partition to enable AVB chain, e.g., boot or system or vbmeta_mainline.
 define _check-and-set-avb-chain-args
 $(eval part := $(1))
 $(eval PART=$(call to-upper,$(part)))
@@ -2677,20 +2698,27 @@
 $(eval INTERNAL_AVB_MAKE_VBMETA_IMAGE_ARGS += \
     --chain_partition $(part):$($(_rollback_index_location)):$(AVB_CHAIN_KEY_DIR)/$(part).avbpubkey)
 
-# Set rollback_index via footer args
-$(eval _footer_args := $(PART)_FOOTER_ARGS)
-$(eval $($(_footer_args)) += --rollback_index $($(_rollback_index)))
+# Set rollback_index via footer args for non-chained vbmeta image. Chained vbmeta image will pick up
+# the index via a separate flag (e.g. BOARD_AVB_VBMETA_MAINLINE_ROLLBACK_INDEX).
+$(if $(filter $(part),$(part:vbmeta_%=%)),\
+    $(eval _footer_args := $(PART)_FOOTER_ARGS) \
+    $(eval $($(_footer_args)) += --rollback_index $($(_rollback_index))))
 endef
 
 # Checks and sets the required build variables for an AVB partition. The partition will be
 # configured as a chained partition, if BOARD_AVB_<partition>_KEY_PATH is defined. Otherwise the
-# image descriptor will be included into vbmeta.img.
+# image descriptor will be included into vbmeta.img, unless it has been already added to any chained
+# VBMeta image.
 # $(1): Partition name, e.g. boot or system.
 define check-and-set-avb-args
+$(eval _in_chained_vbmeta := $(filter $(1),$(INTERNAL_AVB_PARTITIONS_IN_CHAINED_VBMETA_IMAGES)))
 $(if $(BOARD_AVB_$(call to-upper,$(1))_KEY_PATH),\
+    $(if $(_in_chained_vbmeta),\
+        $(error Chaining partition "$(1)" in chained VBMeta image is not supported)) \
     $(call _check-and-set-avb-chain-args,$(1)),\
-    $(eval INTERNAL_AVB_MAKE_VBMETA_IMAGE_ARGS += \
-        --include_descriptors_from_image $(call images-for-partitions,$(1))))
+    $(if $(_in_chained_vbmeta),,\
+        $(eval INTERNAL_AVB_MAKE_VBMETA_IMAGE_ARGS += \
+            --include_descriptors_from_image $(call images-for-partitions,$(1)))))
 endef
 
 ifdef INSTALLED_BOOTIMAGE_TARGET
@@ -2723,6 +2751,15 @@
 $(eval $(call check-and-set-avb-args,recovery))
 endif
 
+# Not using INSTALLED_VBMETA_MAINLINEIMAGE_TARGET as it won't be set yet.
+ifdef BOARD_AVB_VBMETA_MAINLINE
+$(eval $(call check-and-set-avb-args,vbmeta_mainline))
+endif
+
+ifdef BOARD_AVB_VBMETA_VENDOR
+$(eval $(call check-and-set-avb-args,vbmeta_vendor))
+endif
+
 # Add kernel cmdline descriptor for kernel to mount system.img as root with
 # dm-verity. This works when system.img is either chained or not-chained:
 # - chained: The --setup_as_rootfs_from_kernel option will add dm-verity kernel
@@ -2734,13 +2771,27 @@
 endif
 
 BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --padding_size 4096
+BOARD_AVB_MAKE_VBMETA_MAINLINE_IMAGE_ARGS += --padding_size 4096
+BOARD_AVB_MAKE_VBMETA_VENDOR_IMAGE_ARGS += --padding_size 4096
+
+ifeq (eng,$(filter eng, $(TARGET_BUILD_VARIANT)))
+BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --set_hashtree_disabled_flag
+BOARD_AVB_MAKE_VBMETA_MAINLINE_IMAGE_ARGS += --set_hashtree_disabled_flag
+BOARD_AVB_MAKE_VBMETA_VENDOR_IMAGE_ARGS += --set_hashtree_disabled_flag
+endif
 
 ifdef BOARD_AVB_ROLLBACK_INDEX
 BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --rollback_index $(BOARD_AVB_ROLLBACK_INDEX)
 endif
 
-ifeq (eng,$(filter eng, $(TARGET_BUILD_VARIANT)))
-BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --set_hashtree_disabled_flag
+ifdef BOARD_AVB_VBMETA_MAINLINE_ROLLBACK_INDEX
+BOARD_AVB_MAKE_VBMETA_MAINLINE_IMAGE_ARGS += \
+    --rollback_index $(BOARD_AVB_VBMETA_MAINLINE_ROLLBACK_INDEX)
+endif
+
+ifdef BOARD_AVB_VBMETA_VENDOR_ROLLBACK_INDEX
+BOARD_AVB_MAKE_VBMETA_VENDOR_IMAGE_ARGS += \
+    --rollback_index $(BOARD_AVB_VBMETA_VENDOR_ROLLBACK_INDEX)
 endif
 
 # $(1): the directory to extract public keys to
@@ -2769,8 +2820,50 @@
   $(if $(BOARD_AVB_RECOVERY_KEY_PATH),\
     $(hide) $(AVBTOOL) extract_public_key --key $(BOARD_AVB_RECOVERY_KEY_PATH) \
       --output $(1)/recovery.avbpubkey)
+  $(if $(BOARD_AVB_VBMETA_MAINLINE_KEY_PATH),\
+    $(hide) $(AVBTOOL) extract_public_key --key $(BOARD_AVB_VBMETA_MAINLINE_KEY_PATH) \
+        --output $(1)/vbmeta_mainline.avbpubkey)
+  $(if $(BOARD_AVB_VBMETA_VENDOR_KEY_PATH),\
+    $(hide) $(AVBTOOL) extract_public_key --key $(BOARD_AVB_VBMETA_VENDOR_KEY_PATH) \
+        --output $(1)/vbmeta_vendor.avbpubkey)
 endef
 
+# Builds a chained VBMeta image. This VBMeta image will contain the descriptors for the partitions
+# specified in BOARD_AVB_VBMETA_<NAME>. The built VBMeta image will be included into the top-level
+# vbmeta image as a chained partition. For example, if a target defines `BOARD_AVB_VBMETA_MAINLINE
+# := system product_services`, `vbmeta_mainline.img` will be created that includes the descriptors
+# for `system.img` and `product_services.img`. `vbmeta_mainline.img` itself will be included into
+# `vbmeta.img` as a chained partition.
+# $(1): VBMeta image name, such as "vbmeta_mainline", "vbmeta_vendor" etc.
+# $(2): Output filename.
+define build-chained-vbmeta-image
+  $(call pretty,"Target chained vbmeta image: $@")
+  $(hide) $(AVBTOOL) make_vbmeta_image \
+      $(INTERNAL_AVB_$(call to-upper,$(1))_SIGNING_ARGS) \
+      $(BOARD_AVB_MAKE_$(call to-upper,$(1))_IMAGE_ARGS) \
+      $(foreach image,$(BOARD_AVB_$(call to-upper,$(1))), \
+          --include_descriptors_from_image $(call images-for-partitions,$(image))) \
+      --output $@
+endef
+
+ifdef BOARD_AVB_VBMETA_MAINLINE
+INSTALLED_VBMETA_MAINLINEIMAGE_TARGET := $(PRODUCT_OUT)/vbmeta_mainline.img
+$(INSTALLED_VBMETA_MAINLINEIMAGE_TARGET): \
+		$(AVBTOOL) \
+		$(call images-for-partitions,$(BOARD_AVB_VBMETA_MAINLINE)) \
+		$(BOARD_AVB_VBMETA_MAINLINE_KEY_PATH)
+	$(call build-chained-vbmeta-image,vbmeta_mainline)
+endif
+
+ifdef BOARD_AVB_VBMETA_VENDOR
+INSTALLED_VBMETA_VENDORIMAGE_TARGET := $(PRODUCT_OUT)/vbmeta_vendor.img
+$(INSTALLED_VBMETA_VENDORIMAGE_TARGET): \
+		$(AVBTOOL) \
+		$(call images-for-partitions,$(BOARD_AVB_VBMETA_VENDOR)) \
+		$(BOARD_AVB_VBMETA_VENDOR_KEY_PATH)
+	$(call build-chained-vbmeta-image,vbmeta_vendor)
+endif
+
 define build-vbmetaimage-target
   $(call pretty,"Target vbmeta image: $(INSTALLED_VBMETAIMAGE_TARGET)")
   $(hide) mkdir -p $(AVB_CHAIN_KEY_DIR)
@@ -2797,6 +2890,10 @@
 		$(INSTALLED_ODMIMAGE_TARGET) \
 		$(INSTALLED_DTBOIMAGE_TARGET) \
 		$(INSTALLED_RECOVERYIMAGE_TARGET) \
+		$(INSTALLED_VBMETA_MAINLINEIMAGE_TARGET) \
+		$(INSTALLED_VBMETA_VENDORIMAGE_TARGET) \
+		$(BOARD_AVB_VBMETA_MAINLINE_KEY_PATH) \
+		$(BOARD_AVB_VBMETA_VENDOR_KEY_PATH) \
 		$(BOARD_AVB_KEY_PATH)
 	$(build-vbmetaimage-target)
 
@@ -2804,14 +2901,6 @@
 vbmetaimage-nodeps:
 	$(build-vbmetaimage-target)
 
-else ifeq (true,$(BOARD_BUILD_DISABLED_VBMETAIMAGE))
-BUILT_DISABLED_VBMETAIMAGE := $(PRODUCT_OUT)/vbmeta.img
-
-INSTALLED_VBMETAIMAGE_TARGET := $(BUILT_DISABLED_VBMETAIMAGE)
-$(INSTALLED_VBMETAIMAGE_TARGET): $(AVBTOOL)
-	$(hide) $(AVBTOOL) make_vbmeta_image \
-	  --flag 2 --padding_size 4096 --output $@
-
 endif # BOARD_AVB_ENABLE
 
 # -----------------------------------------------------------------
@@ -3380,6 +3469,20 @@
 	$(hide) echo "avb_recovery_algorithm=$(BOARD_AVB_RECOVERY_ALGORITHM)" >> $(zip_root)/META/misc_info.txt
 	$(hide) echo "avb_recovery_rollback_index_location=$(BOARD_AVB_RECOVERY_ROLLBACK_INDEX_LOCATION)" >> $(zip_root)/META/misc_info.txt
 endif # BOARD_AVB_RECOVERY_KEY_PATH
+ifneq (,$(strip $(BOARD_AVB_VBMETA_MAINLINE)))
+	$(hide) echo "avb_vbmeta_mainline=$(BOARD_AVB_VBMETA_MAINLINE)" >> $(zip_root)/META/misc_info.txt
+	$(hide) echo "avb_vbmeta_mainline_args=$(BOARD_AVB_MAKE_VBMETA_MAINLINE_IMAGE_ARGS)" >> $(zip_root)/META/misc_info.txt
+	$(hide) echo "avb_vbmeta_mainline_key_path=$(BOARD_AVB_VBMETA_MAINLINE_KEY_PATH)" >> $(zip_root)/META/misc_info.txt
+	$(hide) echo "avb_vbmeta_mainline_algorithm=$(BOARD_AVB_VBMETA_MAINLINE_ALGORITHM)" >> $(zip_root)/META/misc_info.txt
+	$(hide) echo "avb_vbmeta_mainline_rollback_index_location=$(BOARD_AVB_VBMETA_MAINLINE_ROLLBACK_INDEX_LOCATION)" >> $(zip_root)/META/misc_info.txt
+endif # BOARD_AVB_VBMETA_MAINLINE
+ifneq (,$(strip $(BOARD_AVB_VBMETA_VENDOR)))
+	$(hide) echo "avb_vbmeta_vendor=$(BOARD_AVB_VBMETA_VENDOR)" >> $(zip_root)/META/misc_info.txt
+	$(hide) echo "avb_vbmeta_vendor_args=$(BOARD_AVB_MAKE_VBMETA_MAINLINE_IMAGE_ARGS)" >> $(zip_root)/META/misc_info.txt
+	$(hide) echo "avb_vbmeta_vendor_key_path=$(BOARD_AVB_VBMETA_VENDOR_KEY_PATH)" >> $(zip_root)/META/misc_info.txt
+	$(hide) echo "avb_vbmeta_vendor_algorithm=$(BOARD_AVB_VBMETA_VENDOR_ALGORITHM)" >> $(zip_root)/META/misc_info.txt
+	$(hide) echo "avb_vbmeta_vendor_rollback_index_location=$(BOARD_AVB_VBMETA_VENDOR_ROLLBACK_INDEX_LOCATION)" >> $(zip_root)/META/misc_info.txt
+endif # BOARD_AVB_VBMETA_VENDOR_KEY_PATH
 endif # BOARD_AVB_ENABLE
 ifdef BOARD_BPT_INPUT_FILES
 	$(hide) echo "board_bpt_enable=true" >> $(zip_root)/META/misc_info.txt
@@ -3416,14 +3519,6 @@
 	@# If breakpad symbols have been generated, add them to the zip.
 	$(hide) $(ACP) -r $(TARGET_OUT_BREAKPAD) $(zip_root)/BREAKPAD
 endif
-# BOARD_BUILD_DISABLED_VBMETAIMAGE is used to build a special vbmeta.img
-# that disables AVB verification. The content is fixed and we can just copy
-# it to $(zip_root)/IMAGES without passing some info into misc_info.txt for
-# regeneration.
-ifeq (true,$(BOARD_BUILD_DISABLED_VBMETAIMAGE))
-	$(hide) mkdir -p $(zip_root)/IMAGES
-	$(hide) cp $(INSTALLED_VBMETAIMAGE_TARGET) $(zip_root)/IMAGES/
-endif
 ifdef BOARD_PREBUILT_VENDORIMAGE
 	$(hide) mkdir -p $(zip_root)/IMAGES
 	$(hide) cp $(INSTALLED_VENDORIMAGE_TARGET) $(zip_root)/IMAGES/
diff --git a/core/main.mk b/core/main.mk
index fd62a98..1b00124 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -1391,7 +1391,7 @@
 .PHONY: docs
 docs: $(ALL_DOCS)
 
-.PHONY: sdk
+.PHONY: sdk win_sdk winsdk-tools
 ALL_SDK_TARGETS := $(INTERNAL_SDK_TARGET)
 sdk: $(ALL_SDK_TARGETS)
 $(call dist-for-goals,sdk win_sdk, \
diff --git a/core/tasks/sdk-addon.mk b/core/tasks/sdk-addon.mk
index 2a20f07..29abf48 100644
--- a/core/tasks/sdk-addon.mk
+++ b/core/tasks/sdk-addon.mk
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+.PHONY: sdk_addon
 
 # If they didn't define PRODUCT_SDK_ADDON_NAME, then we won't define
 # any of these rules.
@@ -121,7 +122,6 @@
 	$(hide) $(SOONG_ZIP) -o $@ -C $(dir $(PRIVATE_STAGING_DIR)) -D $(PRIVATE_STAGING_DIR)
 
 
-.PHONY: sdk_addon
 sdk_addon: $(full_target) $(full_target_img)
 
 ifneq ($(sdk_repo_goal),)
diff --git a/target/board/BoardConfigEmuCommon.mk b/target/board/BoardConfigEmuCommon.mk
index ca2176c..a1d5cde 100644
--- a/target/board/BoardConfigEmuCommon.mk
+++ b/target/board/BoardConfigEmuCommon.mk
@@ -28,8 +28,9 @@
 TARGET_COPY_OUT_VENDOR := vendor
 
 # ~100 MB vendor image. Please adjust system image / vendor image sizes
-# when finalizing them.
-BOARD_VENDORIMAGE_PARTITION_SIZE := 100000000
+# when finalizing them. The partition size needs to be a multiple of image
+# block size: 4096.
+BOARD_VENDORIMAGE_PARTITION_SIZE := 100003840
 BOARD_VENDORIMAGE_FILE_SYSTEM_TYPE := ext4
 BOARD_FLASH_BLOCK_SIZE := 512
 DEVICE_MATRIX_FILE   := device/generic/goldfish/compatibility_matrix.xml
diff --git a/target/board/BoardConfigGsiCommon.mk b/target/board/BoardConfigGsiCommon.mk
index c1f3627..1df981b 100644
--- a/target/board/BoardConfigGsiCommon.mk
+++ b/target/board/BoardConfigGsiCommon.mk
@@ -10,18 +10,28 @@
 # we explicit specify this need below (even though it's the current default).
 TARGET_USERIMAGES_SPARSE_EXT_DISABLED := false
 
-# Enable dyanmic system image size and reserved 64MB in it.
-BOARD_SYSTEMIMAGE_PARTITION_RESERVED_SIZE := 67108864
+# Enable dynamic system image size and reserved 128MB in it.
+# Currently the reserve size includes verified boot metadata.
+# TODO: adjust to a smaller value if the reserved size is only for file system.
+BOARD_SYSTEMIMAGE_PARTITION_RESERVED_SIZE := 134217728
 
 # Android Verified Boot (AVB):
-#   Builds a special vbmeta.img that disables AVB verification.
-#   Otherwise, AVB will prevent the device from booting the generic system.img.
-#   Also checks that BOARD_AVB_ENABLE is not set, to prevent adding verity
-#   metadata into system.img.
-ifeq ($(BOARD_AVB_ENABLE),true)
-$(error BOARD_AVB_ENABLE cannot be set for GSI)
-endif
-BOARD_BUILD_DISABLED_VBMETAIMAGE := true
+#   1) Sets BOARD_AVB_ENABLE to sign the GSI image.
+#   2) Sets AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED (--flag 2) in
+#      vbmeta.img to disable AVB verification.
+#
+# To disable AVB for GSI, use the vbmeta.img and the GSI together.
+# To enable AVB for GSI, include the GSI public key into the device-specific
+# vbmeta.img.
+BOARD_AVB_ENABLE := true
+BOARD_AVB_ROLLBACK_INDEX := $(PLATFORM_SECURITY_PATCH_TIMESTAMP)
+BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --flag 2
+
+# Enable chain partition for system.
+BOARD_AVB_SYSTEM_KEY_PATH := external/avb/test/data/testkey_rsa2048.pem
+BOARD_AVB_SYSTEM_ALGORITHM := SHA256_RSA2048
+BOARD_AVB_SYSTEM_ROLLBACK_INDEX := $(PLATFORM_SECURITY_PATCH_TIMESTAMP)
+BOARD_AVB_SYSTEM_ROLLBACK_INDEX_LOCATION := 1
 
 ifneq (,$(filter userdebug eng,$(TARGET_BUILD_VARIANT)))
 # GSI is always userdebug and needs a couple of properties taking precedence
diff --git a/target/board/treble_common.mk b/target/board/treble_common.mk
index daa0f4c..1869000 100644
--- a/target/board/treble_common.mk
+++ b/target/board/treble_common.mk
@@ -35,8 +35,10 @@
 TARGET_USERIMAGES_USE_F2FS := true
 TARGET_USERIMAGES_SPARSE_EXT_DISABLED := false
 
-# Enable dyanmic system image size and reserved 64MB in it.
-BOARD_SYSTEMIMAGE_PARTITION_RESERVED_SIZE := 67108864
+# Enable dynamic system image size and reserved 128MB in it.
+# Currently the reserve size includes verified boot metadata.
+# TODO: adjust to a smaller value if the reserved size is only for file system.
+BOARD_SYSTEMIMAGE_PARTITION_RESERVED_SIZE := 134217728
 
 # Generic AOSP image always requires separate vendor.img
 TARGET_COPY_OUT_VENDOR := vendor
@@ -53,11 +55,19 @@
 USE_XML_AUDIO_POLICY_CONF := 1
 
 # Android Verified Boot (AVB):
-#   Builds a special vbmeta.img that disables AVB verification.
-#   Otherwise, AVB will prevent the device from booting the generic system.img.
-#   Also checks that BOARD_AVB_ENABLE is not set, to prevent adding verity
-#   metadata into system.img.
-ifeq ($(BOARD_AVB_ENABLE),true)
-$(error BOARD_AVB_ENABLE cannot be set for Treble GSI)
-endif
-BOARD_BUILD_DISABLED_VBMETAIMAGE := true
+#   1) Sets BOARD_AVB_ENABLE to sign the GSI image.
+#   2) Sets AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED (--flag 2) in
+#      vbmeta.img to disable AVB verification.
+#
+# To disable AVB for GSI, use the vbmeta.img and the GSI together.
+# To enable AVB for GSI, include the GSI public key into the device-specific
+# vbmeta.img.
+BOARD_AVB_ENABLE := true
+BOARD_AVB_ROLLBACK_INDEX := $(PLATFORM_SECURITY_PATCH_TIMESTAMP)
+BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --flag 2
+
+# Enable chain partition for system.
+BOARD_AVB_SYSTEM_KEY_PATH := external/avb/test/data/testkey_rsa2048.pem
+BOARD_AVB_SYSTEM_ALGORITHM := SHA256_RSA2048
+BOARD_AVB_SYSTEM_ROLLBACK_INDEX := $(PLATFORM_SECURITY_PATCH_TIMESTAMP)
+BOARD_AVB_SYSTEM_ROLLBACK_INDEX_LOCATION := 1
diff --git a/tools/releasetools/add_img_to_target_files.py b/tools/releasetools/add_img_to_target_files.py
index 9e8b698..e9419fe 100755
--- a/tools/releasetools/add_img_to_target_files.py
+++ b/tools/releasetools/add_img_to_target_files.py
@@ -393,32 +393,46 @@
     cmd.extend(["--include_descriptors_from_image", image])
 
 
-def AddVBMeta(output_zip, partitions):
-  """Creates a VBMeta image and store it in output_zip.
+def AddVBMeta(output_zip, partitions, name, needed_partitions):
+  """Creates a VBMeta image and stores it in output_zip.
+
+  It generates the requested VBMeta image. The requested image could be for
+  top-level or chained VBMeta image, which is determined based on the name.
 
   Args:
     output_zip: The output zip file, which needs to be already open.
     partitions: A dict that's keyed by partition names with image paths as
         values. Only valid partition names are accepted, as listed in
         common.AVB_PARTITIONS.
+    name: Name of the VBMeta partition, e.g. 'vbmeta', 'vbmeta_mainline'.
+    needed_partitions: Partitions whose descriptors should be included into the
+        generated VBMeta image.
+
+  Raises:
+    AssertionError: On invalid input args.
   """
-  img = OutputFile(output_zip, OPTIONS.input_tmp, "IMAGES", "vbmeta.img")
+  assert needed_partitions, "Needed partitions must be specified"
+
+  img = OutputFile(
+      output_zip, OPTIONS.input_tmp, "IMAGES", "{}.img".format(name))
   if os.path.exists(img.input_name):
-    print("vbmeta.img already exists; not rebuilding...")
+    print("{}.img already exists; not rebuilding...".format(name))
     return img.input_name
 
   avbtool = os.getenv('AVBTOOL') or OPTIONS.info_dict["avb_avbtool"]
   cmd = [avbtool, "make_vbmeta_image", "--output", img.name]
-  common.AppendAVBSigningArgs(cmd, "vbmeta")
+  common.AppendAVBSigningArgs(cmd, name)
 
   for partition, path in partitions.items():
+    if partition not in needed_partitions:
+      continue
     assert partition in common.AVB_PARTITIONS, \
         'Unknown partition: {}'.format(partition)
     assert os.path.exists(path), \
         'Failed to find {} for {}'.format(path, partition)
     AppendVBMetaArgsForPartition(cmd, partition, path)
 
-  args = OPTIONS.info_dict.get("avb_vbmeta_args")
+  args = OPTIONS.info_dict.get("avb_{}_args".format(name))
   if args and args.strip():
     split_args = shlex.split(args)
     for index, arg in enumerate(split_args[:-1]):
@@ -439,7 +453,7 @@
             split_args[index + 1] = alt_path
             found = True
             break
-        assert found, 'failed to find %s' % (image_path,)
+        assert found, 'Failed to find {}'.format(image_path)
     cmd.extend(split_args)
 
   p = common.Run(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
@@ -693,8 +707,8 @@
                 os.path.exists(os.path.join(OPTIONS.input_tmp, "IMAGES",
                                             "vendor.img")))
   has_odm = (os.path.isdir(os.path.join(OPTIONS.input_tmp, "ODM")) or
-                 os.path.exists(os.path.join(OPTIONS.input_tmp, "IMAGES",
-                                             "odm.img")))
+             os.path.exists(os.path.join(OPTIONS.input_tmp, "IMAGES",
+                                         "odm.img")))
   has_product = (os.path.isdir(os.path.join(OPTIONS.input_tmp, "PRODUCT")) or
                  os.path.exists(os.path.join(OPTIONS.input_tmp, "IMAGES",
                                              "product.img")))
@@ -806,8 +820,33 @@
     partitions['dtbo'] = AddDtbo(output_zip)
 
   if OPTIONS.info_dict.get("avb_enable") == "true":
+    # vbmeta_partitions includes the partitions that should be included into
+    # top-level vbmeta.img, which are the ones that are not included in any
+    # chained VBMeta image plus the chained VBMeta images themselves.
+    vbmeta_partitions = common.AVB_PARTITIONS[:]
+
+    vbmeta_mainline = OPTIONS.info_dict.get("avb_vbmeta_mainline", "").strip()
+    if vbmeta_mainline:
+      banner("vbmeta_mainline")
+      AddVBMeta(
+          output_zip, partitions, "vbmeta_mainline", vbmeta_mainline.split())
+      vbmeta_partitions = [
+          item for item in vbmeta_partitions
+          if item not in vbmeta_mainline.split()]
+      vbmeta_partitions.append("vbmeta_mainline")
+
+    vbmeta_vendor = OPTIONS.info_dict.get("avb_vbmeta_vendor", "").strip()
+    if vbmeta_vendor:
+      banner("vbmeta_vendor")
+      AddVBMeta(
+          output_zip, partitions, "vbmeta_vendor", vbmeta_vendor.split())
+      vbmeta_partitions = [
+          item for item in vbmeta_partitions
+          if item not in vbmeta_vendor.split()]
+      vbmeta_partitions.append("vbmeta_vendor")
+
     banner("vbmeta")
-    AddVBMeta(output_zip, partitions)
+    AddVBMeta(output_zip, partitions, "vbmeta", vbmeta_partitions)
 
   if OPTIONS.info_dict.get("super_size"):
     banner("super_empty")
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index 8d51df6..ee2c6f4 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -408,7 +408,7 @@
     cmd.extend(["--key", key_path, "--algorithm", algorithm])
   avb_salt = OPTIONS.info_dict.get("avb_salt")
   # make_vbmeta_image doesn't like "--salt" (and it's not needed).
-  if avb_salt and partition != "vbmeta":
+  if avb_salt and not partition.startswith("vbmeta"):
     cmd.extend(["--salt", avb_salt])