diff --git a/arm/unittests.cfg b/arm/unittests.cfg
index fe601cbb1..54cedea28 100644
--- a/arm/unittests.cfg
+++ b/arm/unittests.cfg
@@ -1,28 +1,10 @@
 ##############################################################################
 # unittest configuration
 #
-# [unittest_name]
-# file = <name>.flat		# Name of the flat file to be used.
-# smp  = <num>			# Number of processors the VM will use
-#				# during this test. Use $MAX_SMP to use
-#				# the maximum the host supports. Defaults
-#				# to one.
-# extra_params = -append <params...>	# Additional parameters used.
-# arch = arm|arm64			# Select one if the test case is
-#					# specific to only one.
-# groups = <group_name1> <group_name2> ...	# Used to identify test cases
-#						# with run_tests -g ...
-#						# Specify group_name=nodefault
-#						# to have test not run by
-#						# default
-# accel = kvm|tcg		# Optionally specify if test must run with
-#				# kvm or tcg. If not specified, then kvm will
-#				# be used when available.
-# timeout = <duration>		# Optionally specify a timeout.
-# check = <path>=<value> # check a file for a particular value before running
-#                        # a test. The check line can contain multiple files
-#                        # to check separated by a space but each check
-#                        # parameter needs to be of the form <path>=<value>
+# arm specifics:
+#
+# file = <name>.flat            # arm uses .flat files
+# arch = arm|arm64
 ##############################################################################
 
 #
diff --git a/docs/unittests.txt b/docs/unittests.txt
new file mode 100644
index 000000000..53e02077c
--- /dev/null
+++ b/docs/unittests.txt
@@ -0,0 +1,89 @@
+unittests
+*********
+
+run_tests.sh is driven by the <arch>/unittests.cfg file. That file defines
+test cases by specifying an executable (target image) under the <arch>/
+directory, and how to run it. This way, for example, a single file can
+provide multiple test cases by being run with different host configurations
+and/or different parameters passed to it.
+
+Detailed output from run_tests.sh unit tests are stored in files under
+the logs/ directory.
+
+unittests.cfg format
+====================
+
+# is the comment symbol, all following contents of the line is ignored.
+
+Each unit test is defined as with a [unit-test-name] line, followed by
+a set of parameters that control how the test case is run. The name is
+arbitrary and appears in the status reporting output.
+
+Parameters appear on their own lines under the test name, and have a
+param = value format.
+
+Available parameters
+====================
+Note! Some parameters like smp and extra_params modify how a test is run,
+while others like arch and accel restrict the configurations in which the
+test is run.
+
+file
+----
+file = <filename>
+
+This parameter is mandatory and specifies which binary under the <arch>/
+directory to run. Typically this is <name>.flat or <name>.elf, depending
+on the arch. The directory name is not included, only the file name.
+
+arch
+----
+For <arch>/ directories that support multiple architectures, this restricts
+the test to the specified arch. By default, the test will run on any
+architecture.
+
+smp
+---
+smp = <number>
+
+Optional, the number of processors created in the machine to run the test.
+Defaults to 1. $MAX_SMP can be used to specify the maximum supported.
+
+extra_params
+------------
+These are extra parameters supplied to the QEMU process. -append '...' can
+be used to pass arguments into the test case argv. Multiple parameters can
+be added, for example:
+
+extra_params = -m 256 -append 'smp=2'
+
+groups
+------
+groups = <group_name1> <group_name2> ...
+
+Used to group the test cases for the `run_tests.sh -g ...` run group
+option. Adding a test to the nodefault group will cause it to not be
+run by default.
+
+accel
+-----
+accel = kvm|tcg
+
+This restricts the test to the specified accelerator. By default, the
+test will run on either accelerator. (Note, the accelerator can be
+specified with ACCEL= environment variable, and defaults to KVM if
+available).
+
+timeout
+-------
+timeout = <duration>
+
+Optional timeout in seconds, after which the test will be killed and fail.
+
+check
+-----
+check = <path>=<<value>
+
+Check a file for a particular value before running a test. The check line
+can contain multiple files to check separated by a space, but each check
+parameter needs to be of the form <path>=<value>
diff --git a/powerpc/unittests.cfg b/powerpc/unittests.cfg
index e65217c18..432c81d58 100644
--- a/powerpc/unittests.cfg
+++ b/powerpc/unittests.cfg
@@ -1,28 +1,9 @@
 ##############################################################################
 # unittest configuration
 #
-# [unittest_name]
-# file = <name>.flat		# Name of the flat file to be used.
-# smp  = <num>			# Number of processors the VM will use
-#				# during this test. Use $MAX_SMP to use
-#				# the maximum the host supports. Defaults
-#				# to one.
-# extra_params = -append <params...>	# Additional parameters used.
-# arch = ppc64				# Select one if the test case is
-#					# specific to only one.
-# groups = <group_name1> <group_name2> ...	# Used to identify test cases
-#						# with run_tests -g ...
-#						# Specify group_name=nodefault
-#						# to have test not run by
-#						# default
-# accel = kvm|tcg		# Optionally specify if test must run with
-#				# kvm or tcg. If not specified, then kvm will
-#				# be used when available.
-# timeout = <duration>		# Optionally specify a timeout.
-# check = <path>=<value> # check a file for a particular value before running
-#                        # a test. The check line can contain multiple files
-#                        # to check separated by a space but each check
-#                        # parameter needs to be of the form <path>=<value>
+# powerpc specifics:
+#
+# file = <name>.elf             # powerpc uses .elf files
 ##############################################################################
 
 #
diff --git a/riscv/unittests.cfg b/riscv/unittests.cfg
index 5a23bed9c..50c67e37f 100644
--- a/riscv/unittests.cfg
+++ b/riscv/unittests.cfg
@@ -1,28 +1,10 @@
 ##############################################################################
 # unittest configuration
 #
-# [unittest_name]
-# file = <name>.flat		# Name of the flat file to be used.
-# smp  = <num>			# Number of processors the VM will use
-#				# during this test. Use $MAX_SMP to use
-#				# the maximum the host supports. Defaults
-#				# to one.
-# extra_params = -append <params...>	# Additional parameters used.
-# arch = riscv32|riscv64		# Select one if the test case is
-#					# specific to only one.
-# groups = <group_name1> <group_name2> ...	# Used to identify test cases
-#						# with run_tests -g ...
-#						# Specify group_name=nodefault
-#						# to have test not run by
-#						# default
-# accel = kvm|tcg		# Optionally specify if test must run with
-#				# kvm or tcg. If not specified, then kvm will
-#				# be used when available.
-# timeout = <duration>		# Optionally specify a timeout.
-# check = <path>=<value> # check a file for a particular value before running
-#                        # a test. The check line can contain multiple files
-#                        # to check separated by a space but each check
-#                        # parameter needs to be of the form <path>=<value>
+# riscv specifics:
+#
+# file = <name>.flat            # riscv uses .flat files
+# arch = riscv32|risc64
 ##############################################################################
 
 [selftest]
diff --git a/s390x/unittests.cfg b/s390x/unittests.cfg
index 550eff787..d6abf72f3 100644
--- a/s390x/unittests.cfg
+++ b/s390x/unittests.cfg
@@ -1,21 +1,9 @@
 ##############################################################################
 # unittest configuration
 #
-# [unittest_name]
-# file = <name>.elf		# Name of the elf file to be used.
-# extra_params = -append <params...>	# Additional parameters used.
-# groups = <group_name1> <group_name2> ... # Used to identify test cases
-#					   # with run_tests -g ...
-#					   # Specify group_name=nodefault
-#					   # to have test not run by default
-# accel = kvm|tcg		# Optionally specify if test must run with
-#				# kvm or tcg. If not specified, then kvm will
-#				# be used when available.
-# timeout = <duration>		# Optionally specify a timeout.
-# check = <path>=<value> # check a file for a particular value before running
-#			 # a test. The check line can contain multiple files
-#			 # to check separated by a space but each check
-#			 # parameter needs to be of the form <path>=<value>
+# s390x specifics:
+#
+# file = <name>.elf             # s390x uses .elf files
 ##############################################################################
 
 [selftest-setup]
diff --git a/x86/unittests.cfg b/x86/unittests.cfg
index 124be7a1f..867a8ea2f 100644
--- a/x86/unittests.cfg
+++ b/x86/unittests.cfg
@@ -1,28 +1,10 @@
 ##############################################################################
 # unittest configuration
 #
-# [unittest_name]
-# file = <name>.flat		# Name of the flat file to be used.
-# smp  = <num>			# Number of processors the VM will use
-#				# during this test. Use $MAX_SMP to use
-#				# the maximum the host supports. Defaults
-#				# to one.
-# extra_params = -append <params...>	# Additional parameters used.
-# arch = i386|x86_64			# Select one if the test case is
-#					# specific to only one.
-# groups = <group_name1> <group_name2> ...	# Used to identify test cases
-#						# with run_tests -g ...
-#						# Specify group_name=nodefault
-#						# to have test not run by
-#						# default
-# accel = kvm|tcg		# Optionally specify if test must run with
-#				# kvm or tcg. If not specified, then kvm will
-#				# be used when available.
-# timeout = <duration>		# Optionally specify a timeout.
-# check = <path>=<value> # check a file for a particular value before running
-#                        # a test. The check line can contain multiple files
-#                        # to check separated by a space but each check
-#                        # parameter needs to be of the form <path>=<value>
+# x86 specifics:
+#
+# file = <name>.flat            # x86 uses .flat files
+# arch = i386|x86_64
 ##############################################################################
 
 [apic-split]
