selftests/x86/xstate: Refactor context switching test

The existing context switching and ptrace tests in amx.c are not specific
to dynamic states, making them reusable for general xstate testing.

As a first step, move the context switching test to xstate.c. Refactor
the test code to allow specifying which xstate component being tested.

To decouple the test from dynamic states, remove the permission request
code. In fact, The permission request inside the test wrapper was
redundant.

Additionally, replace fatal_error() with ksft_exit_fail_msg() for
consistency in error handling.

  Expected output:
  $ amx_64
  ...
  [RUN]   AMX Tile data: check context switches, 10 iterations, 5 threads.
  [OK]    No incorrect case was found.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250226010731.2456-5-chang.seok.bae@intel.com

Author: ChangSeokBae

tools/testing/selftests/x86/Makefile

@@ -132,3 +132,5 @@ $(OUTPUT)/check_initial_reg_state_64: CFLAGS += -Wl,-ereal_start -static
 
 $(OUTPUT)/nx_stack_32: CFLAGS += -Wl,-z,noexecstack
 $(OUTPUT)/nx_stack_64: CFLAGS += -Wl,-z,noexecstack
+
+$(OUTPUT)/amx_64: EXTRA_FILES += xstate.c

tools/testing/selftests/x86/amx.c

@@ -3,7 +3,6 @@
 #define _GNU_SOURCE
 #include <err.h>
 #include <errno.h>
-#include <pthread.h>
 #include <setjmp.h>
 #include <stdio.h>
 #include <string.h>
@@ -434,14 +433,6 @@ static inline bool __validate_tiledata_regs(struct xsave_buffer *xbuf1)
 	return true;
 }
 
-static inline void validate_tiledata_regs_same(struct xsave_buffer *xbuf)
-{
-	int ret = __validate_tiledata_regs(xbuf);
-
-	if (ret != 0)
-		fatal_error("TILEDATA registers changed");
-}
-
 static inline void validate_tiledata_regs_changed(struct xsave_buffer *xbuf)
 {
 	int ret = __validate_tiledata_regs(xbuf);
@@ -498,158 +489,6 @@ static void test_fork(void)
 	_exit(0);
 }
 
-/* Context switching test */
-
-static struct _ctxtswtest_cfg {
-	unsigned int iterations;
-	unsigned int num_threads;
-} ctxtswtest_config;
-
-struct futex_info {
-	pthread_t thread;
-	int nr;
-	pthread_mutex_t mutex;
-	struct futex_info *next;
-};
-
-static void *check_tiledata(void *info)
-{
-	struct futex_info *finfo = (struct futex_info *)info;
-	struct xsave_buffer *xbuf;
-	int i;
-
-	xbuf = alloc_xbuf();
-	if (!xbuf)
-		fatal_error("unable to allocate XSAVE buffer");
-
-	/*
-	 * Load random data into 'xbuf' and then restore
-	 * it to the tile registers themselves.
-	 */
-	load_rand_tiledata(xbuf);
-	for (i = 0; i < ctxtswtest_config.iterations; i++) {
-		pthread_mutex_lock(&finfo->mutex);
-
-		/*
-		 * Ensure the register values have not
-		 * diverged from those recorded in 'xbuf'.
-		 */
-		validate_tiledata_regs_same(xbuf);
-
-		/* Load new, random values into xbuf and registers */
-		load_rand_tiledata(xbuf);
-
-		/*
-		 * The last thread's last unlock will be for
-		 * thread 0's mutex.  However, thread 0 will
-		 * have already exited the loop and the mutex
-		 * will already be unlocked.
-		 *
-		 * Because this is not an ERRORCHECK mutex,
-		 * that inconsistency will be silently ignored.
-		 */
-		pthread_mutex_unlock(&finfo->next->mutex);
-	}
-
-	free(xbuf);
-	/*
-	 * Return this thread's finfo, which is
-	 * a unique value for this thread.
-	 */
-	return finfo;
-}
-
-static int create_threads(int num, struct futex_info *finfo)
-{
-	int i;
-
-	for (i = 0; i < num; i++) {
-		int next_nr;
-
-		finfo[i].nr = i;
-		/*
-		 * Thread 'i' will wait on this mutex to
-		 * be unlocked.  Lock it immediately after
-		 * initialization:
-		 */
-		pthread_mutex_init(&finfo[i].mutex, NULL);
-		pthread_mutex_lock(&finfo[i].mutex);
-
-		next_nr = (i + 1) % num;
-		finfo[i].next = &finfo[next_nr];
-
-		if (pthread_create(&finfo[i].thread, NULL, check_tiledata, &finfo[i]))
-			fatal_error("pthread_create()");
-	}
-	return 0;
-}
-
-static void affinitize_cpu0(void)
-{
-	cpu_set_t cpuset;
-
-	CPU_ZERO(&cpuset);
-	CPU_SET(0, &cpuset);
-
-	if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0)
-		fatal_error("sched_setaffinity to CPU 0");
-}
-
-static void test_context_switch(void)
-{
-	struct futex_info *finfo;
-	int i;
-
-	/* Affinitize to one CPU to force context switches */
-	affinitize_cpu0();
-
-	req_xtiledata_perm();
-
-	printf("[RUN]\tCheck tiledata context switches, %d iterations, %d threads.\n",
-	       ctxtswtest_config.iterations,
-	       ctxtswtest_config.num_threads);
-
-
-	finfo = malloc(sizeof(*finfo) * ctxtswtest_config.num_threads);
-	if (!finfo)
-		fatal_error("malloc()");
-
-	create_threads(ctxtswtest_config.num_threads, finfo);
-
-	/*
-	 * This thread wakes up thread 0
-	 * Thread 0 will wake up 1
-	 * Thread 1 will wake up 2
-	 * ...
-	 * the last thread will wake up 0
-	 *
-	 * ... this will repeat for the configured
-	 * number of iterations.
-	 */
-	pthread_mutex_unlock(&finfo[0].mutex);
-
-	/* Wait for all the threads to finish: */
-	for (i = 0; i < ctxtswtest_config.num_threads; i++) {
-		void *thread_retval;
-		int rc;
-
-		rc = pthread_join(finfo[i].thread, &thread_retval);
-
-		if (rc)
-			fatal_error("pthread_join() failed for thread %d err: %d\n",
-					i, rc);
-
-		if (thread_retval != &finfo[i])
-			fatal_error("unexpected thread retval for thread %d: %p\n",
-					i, thread_retval);
-
-	}
-
-	printf("[OK]\tNo incorrect case was found.\n");
-
-	free(finfo);
-}
-
 /* Ptrace test */
 
 /*
@@ -745,6 +584,7 @@ static void test_ptrace(void)
 
 int main(void)
 {
+	const unsigned int ctxtsw_num_threads = 5, ctxtsw_iterations = 10;
 	unsigned long features;
 	long rc;
 
@@ -772,9 +612,7 @@ int main(void)
 
 	test_fork();
 
-	ctxtswtest_config.iterations = 10;
-	ctxtswtest_config.num_threads = 5;
-	test_context_switch();
+	test_context_switch(XFEATURE_XTILEDATA, ctxtsw_num_threads, ctxtsw_iterations);
 
 	test_ptrace();