From: Chang S. Bae chang.seok.bae@intel.com
XSAVE state is thread-local. The kernel switches between thread state at context switch time. Generally, running a selftest for a while will naturally expose it to some context switching and and will test the XSAVE code.
Instead of just hoping that the tests get context-switched at random times, force context-switches on purpose. Spawn off a few userspace threads and force context-switches between them. Ensure that the kernel correctly context switches each thread's unique AMX state.
[ dhansen: bunches of cleanups ]
Signed-off-by: Chang S. Bae chang.seok.bae@intel.com Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Cc: Thomas Gleixner tglx@linutronix.de Cc: x86@kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-kselftest@vger.kernel.org ---
b/tools/testing/selftests/x86/amx.c | 160 +++++++++++++++++++++++++++++++++++- 1 file changed, 157 insertions(+), 3 deletions(-)
diff -puN tools/testing/selftests/x86/amx.c~amx-selftest-2_3-selftest-x86-amx-Add-context-switch-test tools/testing/selftests/x86/amx.c --- a/tools/testing/selftests/x86/amx.c~amx-selftest-2_3-selftest-x86-amx-Add-context-switch-test 2021-10-15 13:56:41.453901715 -0700 +++ b/tools/testing/selftests/x86/amx.c 2021-10-15 13:56:41.457901715 -0700 @@ -3,6 +3,7 @@ #define _GNU_SOURCE #include <err.h> #include <errno.h> +#include <pthread.h> #include <setjmp.h> #include <stdio.h> #include <string.h> @@ -10,8 +11,6 @@ #include <unistd.h> #include <x86intrin.h>
-#include <linux/futex.h> - #include <sys/auxv.h> #include <sys/mman.h> #include <sys/shm.h> @@ -259,7 +258,6 @@ void sig_print(char *msg)
static volatile bool noperm_signaled; static int noperm_errs; - /* * Signal handler for when AMX is used but * permission has not been obtained. @@ -674,6 +672,158 @@ 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); +} + int main(void) { /* Check hardware availability at first */ @@ -690,6 +840,10 @@ int main(void)
test_fork();
+ ctxtswtest_config.iterations = 10; + ctxtswtest_config.num_threads = 5; + test_context_switch(); + clearhandler(SIGILL); free_stashed_xsave();
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