kho: add test for kexec handover

Testing kexec handover requires a kernel driver that will generate some
data and preserve it with KHO on the first boot and then restore that data
and verify it was preserved properly after kexec.

To facilitate such test, along with the kernel driver responsible for data
generation, preservation and restoration add a script that runs a kernel
in a VM with a minimal /init.  The /init enables KHO, loads a kernel image
for kexec and runs kexec reboot.  After the boot of the kexeced kernel,
the driver verifies that the data was properly preserved.

[rppt@kernel.org: fix section mismatch]
  Link: https://lkml.kernel.org/r/aIiRC8fXiOXKbPM_@kernel.org
Link: https://lkml.kernel.org/r/20250727083733.2590139-1-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Pratyush Yadav <pratyush@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/Kconfig.debug

@@ -3225,6 +3225,27 @@ config TEST_OBJPOOL
 
 	  If unsure, say N.
 
+config TEST_KEXEC_HANDOVER
+	bool "Test for Kexec HandOver"
+	default n
+	depends on KEXEC_HANDOVER
+	help
+	  This option enables test for Kexec HandOver (KHO).
+	  The test consists of two parts: saving kernel data before kexec and
+	  restoring the data after kexec and verifying that it was properly
+	  handed over. This test module creates and saves data on the boot of
+	  the first kernel and restores and verifies the data on the boot of
+	  kexec'ed kernel.
+
+	  For detailed documentation about KHO, see Documentation/core-api/kho.
+
+	  To run the test run:
+
+	  tools/testing/selftests/kho/vmtest.sh -h
+
+	  If unsure, say N.
+
+
 config INT_POW_KUNIT_TEST
 	tristate "Integer exponentiation (int_pow) test" if !KUNIT_ALL_TESTS
 	depends on KUNIT