[6/6] selftests: arm64: Add build and documentation for FP tests

diff --git a/tools/testing/selftests/arm64/Makefile b/tools/testing/selftests/arm64/Makefile
index 93b567d23c8b..a28d4e7c9948 100644
--- a/tools/testing/selftests/arm64/Makefile
+++ b/tools/testing/selftests/arm64/Makefile
@@ -4,7 +4,7 @@ 
 ARCH ?= $(shell uname -m 2>/dev/null || echo not)
 
 ifneq (,$(filter $(ARCH),aarch64 arm64))
-ARM64_SUBTARGETS ?= tags signal
+ARM64_SUBTARGETS ?= tags signal fp
 else
 ARM64_SUBTARGETS :=
 endif
diff --git a/tools/testing/selftests/arm64/fp/.gitignore b/tools/testing/selftests/arm64/fp/.gitignore
new file mode 100644
index 000000000000..d66f76d2a650
--- /dev/null
+++ b/tools/testing/selftests/arm64/fp/.gitignore
@@ -0,0 +1,5 @@ 
+fpsimd-test
+sve-probe-vls
+sve-ptrace
+sve-test
+vlset
diff --git a/tools/testing/selftests/arm64/fp/Makefile b/tools/testing/selftests/arm64/fp/Makefile
new file mode 100644
index 000000000000..a57009d3a0dc
--- /dev/null
+++ b/tools/testing/selftests/arm64/fp/Makefile
@@ -0,0 +1,17 @@ 
+# SPDX-License-Identifier: GPL-2.0
+
+CFLAGS += -I../../../../../usr/include/
+TEST_GEN_PROGS := sve-ptrace sve-probe-vls
+TEST_PROGS_EXTENDED := fpsimd-test fpsimd-stress sve-test sve-stress vlset
+
+all: $(TEST_GEN_PROGS) $(TEST_PROGS_EXTENDED)
+
+fpsimd-test: fpsimd-test.o
+	$(CC) -nostdlib $^ -o $@
+sve-ptrace: sve-ptrace.o sve-ptrace-asm.o
+sve-probe-vls: sve-probe-vls.o
+sve-test: sve-test.o
+	$(CC) -nostdlib $^ -o $@
+vlset: vlset.o
+
+include ../../lib.mk
diff --git a/tools/testing/selftests/arm64/fp/README b/tools/testing/selftests/arm64/fp/README
new file mode 100644
index 000000000000..03e3dad865d8
--- /dev/null
+++ b/tools/testing/selftests/arm64/fp/README
@@ -0,0 +1,100 @@ 
+This directory contains a mix of tests integrated with kselftest and
+standalone stress tests.
+
+kselftest tests
+===============
+
+sve-probe-vls - Checks the SVE vector length enumeration interface
+sve-ptrace - Checks the SVE ptrace interface
+
+Running the non-kselftest tests
+===============================
+
+sve-stress performs an SVE context switch stress test, as described
+below.
+
+(The fpsimd-stress test works the same way; just substitute "fpsimd" for
+"sve" in the following commands.)
+
+
+The test runs until killed by the user.
+
+If no context switch error was detected, you will see output such as
+the following:
+
+$ ./sve-stress
+(wait for some time)
+^C
+Vector length:        512 bits
+PID:    1573
+Terminated by signal 15, no error, iterations=9467, signals=1014
+Vector length:  512 bits
+PID:    1575
+Terminated by signal 15, no error, iterations=9448, signals=1028
+Vector length:  512 bits
+PID:    1577
+Terminated by signal 15, no error, iterations=9436, signals=1039
+Vector length:  512 bits
+PID:    1579
+Terminated by signal 15, no error, iterations=9421, signals=1039
+Vector length:  512 bits
+PID:    1581
+Terminated by signal 15, no error, iterations=9403, signals=1039
+Vector length:  512 bits
+PID:    1583
+Terminated by signal 15, no error, iterations=9385, signals=1036
+Vector length:  512 bits
+PID:    1585
+Terminated by signal 15, no error, iterations=9376, signals=1039
+Vector length:  512 bits
+PID:    1587
+Terminated by signal 15, no error, iterations=9361, signals=1039
+Vector length:  512 bits
+PID:    1589
+Terminated by signal 15, no error, iterations=9350, signals=1039
+
+
+If an error was detected, details of the mismatch will be printed
+instead of "no error".
+
+Ideally, the test should be allowed to run for many minutes or hours
+to maximise test coverage.
+
+
+KVM stress testing
+==================
+
+To try to reproduce the bugs that we have been observing, sve-stress
+should be run in parallel in two KVM guests, while simultaneously
+running on the host.
+
+1) Start 2 guests, using the following command for each:
+
+$ lkvm run --console=virtio -pconsole=hvc0 --sve Image
+
+(Depending on the hardware GIC implementation, you may also need
+--irqchip=gicv3.  New kvmtool defaults to that if appropriate, but I
+can't remember whether my branch is new enough for that.  Try without
+the option first.)
+
+Kvmtool occupies the terminal until you kill it (Ctrl+A x),
+or until the guest terminates.  It is therefore recommended to run
+each instance in separate terminal (use screen or ssh etc.)  This
+allows multiple guests to be run in parallel while running other
+commands on the host.
+
+Within the guest, the host filesystem is accessible, mounted on /host.
+
+2) Run the sve-stress on *each* guest with the Vector-Length set to 32:
+guest$ ./vlset --inherit 32 ./sve-stress
+
+3) Run the sve-stress on the host with the maximum Vector-Length:
+host$ ./vlset --inherit --max ./sve-stress
+
+
+Again, the test should be allowed to run for many minutes or hours to
+maximise test coverage.
+
+If no error is detected, you will see output from each sve-stress
+instance similar to that illustrated above; otherwise details of the
+observed mismatches will be printed.