From: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
AMX TILEDATA is a very large XSAVE feature. It could have caused
nasty space XSAVE buffer space waste in two places:
* Signal stacks
* Kernel task_struct->fpu buffers
To avoid this waste, neither of these buffers have AMX state by
default. The non-default features are called "dynamic" features.
There is an arch_prctl(ARCH_REQ_XCOMP_PERM) which allows a task
to declare that it wants to use AMX or other "dynamic" XSAVE
features. This arch_prctl() ensures that sufficient sigaltstack
space is available before it will succeed. It also expands the
task_struct buffer.
Functions of this test:
* Test arch_prctl(ARCH_REQ_XCOMP_PERM). Ensure that it checks for
proper sigaltstack sizing and that the sizing is enforced for
future sigaltstack calls.
* Ensure that ARCH_REQ_XCOMP_PERM is inherited across fork()
* Ensure that TILEDATA use before the prctl() is fatal
* Ensure that TILEDATA is cleared across fork()
Note: Generally, compiler support is needed to do something with
AMX. Instead, directly load AMX state from userspace with a
plain XSAVE. Do not depend on the compiler.
[ dhansen: bunches of cleanups ]
Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-kselftest@xxxxxxxxxxxxxxx
---
b/tools/testing/selftests/x86/Makefile | 2
b/tools/testing/selftests/x86/amx.c | 697 +++++++++++++++++++++++++++++++++
2 files changed, 698 insertions(+), 1 deletion(-)
diff -puN /dev/null tools/testing/selftests/x86/amx.c
--- /dev/null 2021-10-02 19:44:55.430567491 -0700
+++ b/tools/testing/selftests/x86/amx.c 2021-10-15 13:56:39.829901810 -0700
@@ -0,0 +1,697 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+#include <err.h>
+#include <errno.h>
+#include <setjmp.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include <x86intrin.h>
+
+#include <linux/futex.h>
+
+#include <sys/auxv.h>
+#include <sys/mman.h>
+#include <sys/shm.h>
+#include <sys/syscall.h>
+#include <sys/wait.h>
+
+#ifndef __x86_64__
+# error This test is 64-bit only
+#endif
+
+#define XSAVE_HDR_OFFSET 512
+#define XSAVE_HDR_SIZE 64
+
+struct xsave_buffer {
+ union {
+ struct {
+ char legacy[XSAVE_HDR_OFFSET];
+ char header[XSAVE_HDR_SIZE];
+ char extended[0];
+ };
+ char bytes[0];
+ };
+};
+
+static inline uint64_t xgetbv(uint32_t index)
+{
+ uint32_t eax, edx;
+
+ asm volatile("xgetbv;"
+ : "=a" (eax), "=d" (edx)
+ : "c" (index));
+ return eax + ((uint64_t)edx << 32);
+}
+
+static inline void cpuid(uint32_t *eax, uint32_t *ebx, uint32_t *ecx, uint32_t *edx)
+{
+ asm volatile("cpuid;"
+ : "=a" (*eax), "=b" (*ebx), "=c" (*ecx), "=d" (*edx)
+ : "0" (*eax), "2" (*ecx));
+}
+
+static inline void xsave(struct xsave_buffer *xbuf, uint64_t rfbm)
+{
+ uint32_t rfbm_lo = rfbm;
+ uint32_t rfbm_hi = rfbm >> 32;
+
+ asm volatile("xsave (%%rdi)"
+ : : "D" (xbuf), "a" (rfbm_lo), "d" (rfbm_hi)
+ : "memory");
+}
+
+static inline void xrstor(struct xsave_buffer *xbuf, uint64_t rfbm)
+{
+ uint32_t rfbm_lo = rfbm;
+ uint32_t rfbm_hi = rfbm >> 32;
+
+ asm volatile("xrstor (%%rdi)"
+ : : "D" (xbuf), "a" (rfbm_lo), "d" (rfbm_hi));
+}
+
+/* err() exits and will not return */
+#define fatal_error(msg, ...) err(1, "[FAIL]\t" msg, ##__VA_ARGS__)
+
+static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
+ int flags)
+{
+ struct sigaction sa;
+
+ memset(&sa, 0, sizeof(sa));
+ sa.sa_sigaction = handler;
+ sa.sa_flags = SA_SIGINFO | flags;
+ sigemptyset(&sa.sa_mask);
+ if (sigaction(sig, &sa, 0))
+ fatal_error("sigaction");
+}
+
+static void clearhandler(int sig)
+{
+ struct sigaction sa;
+
+ memset(&sa, 0, sizeof(sa));
+ sa.sa_handler = SIG_DFL;
+ sigemptyset(&sa.sa_mask);
+ if (sigaction(sig, &sa, 0))
+ fatal_error("sigaction");
+}
+
+#define XFEATURE_XTILECFG 17
+#define XFEATURE_XTILEDATA 18
+#define XFEATURE_MASK_XTILECFG (1 << XFEATURE_XTILECFG)
+#define XFEATURE_MASK_XTILEDATA (1 << XFEATURE_XTILEDATA)
+#define XFEATURE_MASK_XTILE (XFEATURE_MASK_XTILECFG | XFEATURE_MASK_XTILEDATA)
+
+#define CPUID_LEAF1_ECX_XSAVE_MASK (1 << 26)
+#define CPUID_LEAF1_ECX_OSXSAVE_MASK (1 << 27)
+static inline void check_cpuid_xsave(void)
+{
+ uint32_t eax, ebx, ecx, edx;
+
+ /*
+ * CPUID.1:ECX.XSAVE[bit 26] enumerates general
+ * support for the XSAVE feature set, including
+ * XGETBV.
+ */
+ eax = 1;
+ ecx = 0;
+ cpuid(&eax, &ebx, &ecx, &edx);
+ if (!(ecx & CPUID_LEAF1_ECX_XSAVE_MASK))
+ fatal_error("cpuid: no CPU xsave support");
+ if (!(ecx & CPUID_LEAF1_ECX_OSXSAVE_MASK))
+ fatal_error("cpuid: no OS xsave support");
+}
+
+static uint32_t xbuf_size;
+
+static struct {
+ uint32_t xbuf_offset;
+ uint32_t size;
+} xtiledata;
+
+#define CPUID_LEAF_XSTATE 0xd
+#define CPUID_SUBLEAF_XSTATE_USER 0x0
+#define TILE_CPUID 0x1d
+#define TILE_PALETTE_ID 0x1
+
+static void check_cpuid_xtiledata(void)
+{
+ uint32_t eax, ebx, ecx, edx;
+
+ eax = CPUID_LEAF_XSTATE;
+ ecx = CPUID_SUBLEAF_XSTATE_USER;
+ cpuid(&eax, &ebx, &ecx, &edx);
+
+ /*
+ * EBX enumerates the size (in bytes) required by the XSAVE
+ * instruction for an XSAVE area containing all the user state
+ * components corresponding to bits currently set in XCR0.
+ *
+ * Stash that off so it can be used to allocate buffers later.
+ */
+ xbuf_size = ebx;
+
+ eax = CPUID_LEAF_XSTATE;
+ ecx = XFEATURE_XTILEDATA;
+
+ cpuid(&eax, &ebx, &ecx, &edx);
+ /*
+ * eax: XTILEDATA state component size
+ * ebx: XTILEDATA state component offset in user buffer
+ */
+ if (!eax || !ebx)
+ fatal_error("xstate cpuid: invalid tile data size/offset: %d/%d",
+ eax, ebx);
+
+ xtiledata.size = eax;
+ xtiledata.xbuf_offset = ebx;
+}
+
+/* The helpers for managing XSAVE buffer and tile states: */
+
+struct xsave_buffer *alloc_xbuf(void)
+{
+ struct xsave_buffer *xbuf;
+
+ /* XSAVE buffer should be 64B-aligned. */
+ xbuf = aligned_alloc(64, xbuf_size);
+ if (!xbuf)
+ fatal_error("aligned_alloc()");
+ return xbuf;
+}
+
+static inline void clear_xstate_header(struct xsave_buffer *buffer)
+{
+ memset(&buffer->header, 0, sizeof(buffer->header));
+}
+
+static inline uint64_t get_xstatebv(struct xsave_buffer *buffer)
+{
+ /* XSTATE_BV is at the beginning of the header: */
+ return *(uint64_t *)&buffer->header;
+}
+
+static inline void set_xstatebv(struct xsave_buffer *buffer, uint64_t bv)
+{
+ /* XSTATE_BV is at the beginning of the header: */
+ *(uint64_t *)(&buffer->header) = bv;
+}
+
+static void set_rand_tiledata(struct xsave_buffer *xbuf)
+{
+ int *ptr = (int *)&xbuf->bytes[xtiledata.xbuf_offset];
+ int data;
+ int i;
+
+ /*
+ * Ensure that 'data' is never 0. This ensures that
+ * the registers are never in their initial configuration
+ * and thus never tracked as being in the init state.
+ */
+ data = rand() | 1;
+
+ for (i = 0; i < xtiledata.size / sizeof(int); i++, ptr++)
+ *ptr = data;
+}
+
+struct xsave_buffer *stashed_xsave;
+
+static void init_stashed_xsave(void)
+{
+ stashed_xsave = alloc_xbuf();
+ if (!stashed_xsave)
+ fatal_error("failed to allocate stashed_xsave\n");
+ clear_xstate_header(stashed_xsave);
+}
+
+static void free_stashed_xsave(void)
+{
+ free(stashed_xsave);
+}
+
+/* See 'struct _fpx_sw_bytes' at sigcontext.h */
+#define SW_BYTES_OFFSET 464
+/* N.B. The struct's field name varies so read from the offset. */
+#define SW_BYTES_BV_OFFSET (SW_BYTES_OFFSET + 8)
+
+static inline struct _fpx_sw_bytes *get_fpx_sw_bytes(void *buffer)
+{
+ return (struct _fpx_sw_bytes *)(buffer + SW_BYTES_OFFSET);
+}
+
+static inline uint64_t get_fpx_sw_bytes_features(void *buffer)
+{
+ return *(uint64_t *)(buffer + SW_BYTES_BV_OFFSET);
+}
+
+/* Work around printf() being unsafe in signals: */
+#define SIGNAL_BUF_LEN 1000
+char signal_message_buffer[SIGNAL_BUF_LEN];
+void sig_print(char *msg)
+{
+ int left = SIGNAL_BUF_LEN - strlen(signal_message_buffer) - 1;
+
+ strncat(signal_message_buffer, msg, left);
+}
+
+static volatile bool noperm_signaled;
+static int noperm_errs;
+
+/*
+ * Signal handler for when AMX is used but
+ * permission has not been obtained.
+ */
+static void handle_noperm(int sig, siginfo_t *si, void *ctx_void)
+{
+ ucontext_t *ctx = (ucontext_t *)ctx_void;
+ void *xbuf = ctx->uc_mcontext.fpregs;
+ struct _fpx_sw_bytes *sw_bytes;
+ uint64_t features;
+
+ /* Reset the signal message buffer: */
+ signal_message_buffer[0] = '\0';
+ sig_print("\tAt SIGILL handler,\n");
+
+ if (si->si_code != ILL_ILLOPC) {
+ noperm_errs++;
+ sig_print("[FAIL]\tInvalid signal code.\n");
+ } else {
+ sig_print("[OK]\tValid signal code (ILL_ILLOPC).\n");
+ }
+
+ sw_bytes = get_fpx_sw_bytes(xbuf);
+ /*
+ * Without permission, the signal XSAVE buffer should not
+ * have room for AMX register state (aka. xtiledata).
+ * Check that the size does not overlap with where xtiledata
+ * will reside.
+ *
+ * This also implies that no state components *PAST*
+ * XTILEDATA (features >=19) can be present in the buffer.
+ */
+ if (sw_bytes->xstate_size <= xtiledata.xbuf_offset) {
+ sig_print("[OK]\tValid xstate size\n");
+ } else {
+ noperm_errs++;
+ sig_print("[FAIL]\tInvalid xstate size\n");
+ }
+
+ features = get_fpx_sw_bytes_features(xbuf);
+ /*
+ * Without permission, the XTILEDATA feature
+ * bit should not be set.
+ */
+ if ((features & XFEATURE_MASK_XTILEDATA) == 0) {
+ sig_print("[OK]\tValid xstate mask\n");
+ } else {
+ noperm_errs++;
+ sig_print("[FAIL]\tInvalid xstate mask\n");
+ }
+
+ noperm_signaled = true;
+ ctx->uc_mcontext.gregs[REG_RIP] += 3; /* Skip the faulting XRSTOR */
+}
+
+/* Return true if XRSTOR is successful; otherwise, false. */
+static inline bool xrstor_safe(struct xsave_buffer *xbuf, uint64_t mask)
+{
+ noperm_signaled = false;
+ xrstor(xbuf, mask);
+
+ /* Print any messages produced by the signal code: */
+ printf("%s", signal_message_buffer);
+ /*
+ * Reset the buffer to make sure any future printing
+ * only outputs new messages:
+ */
+ signal_message_buffer[0] = '\0';
+
+ if (noperm_errs)
+ fatal_error("saw %d errors in noperm signal handler\n", noperm_errs);
+
+ return !noperm_signaled;
+}
+
+/*
+ * Use XRSTOR to populate the XTILEDATA registers with
+ * random data.
+ *
+ * Return true if successful; otherwise, false.
+ */
+static inline bool load_rand_tiledata(struct xsave_buffer *xbuf)
+{
+ clear_xstate_header(xbuf);
+ set_xstatebv(xbuf, XFEATURE_MASK_XTILEDATA);
+ set_rand_tiledata(xbuf);
+ return xrstor_safe(xbuf, XFEATURE_MASK_XTILEDATA);
+}
+
+/* Return XTILEDATA to its initial configuration. */
+static inline void init_xtiledata(void)
+{
+ clear_xstate_header(stashed_xsave);
+ xrstor_safe(stashed_xsave, XFEATURE_MASK_XTILEDATA);
+}
+
+enum expected_result { FAIL_EXPECTED, SUCCESS_EXPECTED };
+
+/* arch_prctl() and sigaltstack() test */
+
+#define ARCH_GET_XCOMP_PERM 0x1022
+#define ARCH_REQ_XCOMP_PERM 0x1023
+
+static void req_xtiledata_perm(void)
+{
+ syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_PERM, XFEATURE_XTILEDATA);
+}
+
+static void validate_req_xcomp_perm(enum expected_result exp)
+{
+ unsigned long bitmask;
+ long rc;
+
+ rc = syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_PERM, XFEATURE_XTILEDATA);
+ if (exp == FAIL_EXPECTED) {
+ if (rc) {
+ printf("[OK]\tARCH_REQ_XCOMP_PERM saw expected failure..\n");
+ return;
+ }
+
+ fatal_error("ARCH_REQ_XCOMP_PERM saw unexpected success.\n");
+ } else if (rc) {
+ fatal_error("ARCH_REQ_XCOMP_PERM saw unexpected failure.\n");
+ }
+
+ rc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_PERM, &bitmask);
+ if (rc) {
+ fatal_error("prctl(ARCH_GET_XCOMP_PERM) error: %ld", rc);
+ } else if (bitmask & XFEATURE_MASK_XTILE) {
+ printf("\tARCH_REQ_XCOMP_PERM is successful.\n");
+ }
+}
+
+static void validate_xcomp_perm(enum expected_result exp)
+{
+ bool load_success = load_rand_tiledata(stashed_xsave);
+
+ if (exp == FAIL_EXPECTED) {
+ if (load_success) {
+ noperm_errs++;
+ printf("[FAIL]\tLoad tiledata succeeded.\n");
+ } else {
+ printf("[OK]\tLoad tiledata failed.\n");
+ }
+ } else if (exp == SUCCESS_EXPECTED) {
+ if (load_success) {
+ printf("[OK]\tLoad tiledata succeeded.\n");
+ } else {
+ noperm_errs++;
+ printf("[FAIL]\tLoad tiledata failed.\n");
+ }
+ }
+}
+
+#ifndef AT_MINSIGSTKSZ
+# define AT_MINSIGSTKSZ 51
+#endif
+
+static void *alloc_altstack(unsigned int size)
+{
+ void *altstack;
+
+ altstack = mmap(NULL, size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
+
+ if (altstack == MAP_FAILED)
+ fatal_error("mmap() for altstack");
+
+ return altstack;
+}
+
+static void setup_altstack(void *addr, unsigned long size, enum expected_result exp)
+{
+ stack_t ss;
+ int rc;
+
+ memset(&ss, 0, sizeof(ss));
+ ss.ss_size = size;
+ ss.ss_sp = addr;
+
+ rc = sigaltstack(&ss, NULL);
+
+ if (exp == FAIL_EXPECTED) {
+ if (rc) {
+ printf("[OK]\tsigaltstack() failed.\n");
+ } else {
+ fatal_error("sigaltstack() succeeded unexpectedly.\n");
+ }
+ } else if (rc) {
+ fatal_error("sigaltstack()");
+ }
+}
+
+static void test_dynamic_sigaltstack(void)
+{
+ unsigned int small_size, enough_size;
+ unsigned long minsigstksz;
+ void *altstack;
+
+ minsigstksz = getauxval(AT_MINSIGSTKSZ);
+ printf("\tAT_MINSIGSTKSZ = %lu\n", minsigstksz);
+ /*
+ * getauxval() itself can return 0 for failure or
+ * success. But, in this case, AT_MINSIGSTKSZ
+ * will always return a >=0 value if implemented.
+ * Just check for 0.
+ */
+ if (minsigstksz == 0) {
+ printf("no support for AT_MINSIGSTKSZ, skipping sigaltstack tests\n");
+ return;
+ }
+
+ enough_size = minsigstksz * 2;
+
+ altstack = alloc_altstack(enough_size);
+ printf("\tAllocate memory for altstack (%u bytes).\n", enough_size);
+
+ /*
+ * Try setup_altstack() with a size which can not fit
+ * XTILEDATA. ARCH_REQ_XCOMP_PERM should fail.
+ */
+ small_size = minsigstksz - xtiledata.size;
+ printf("\tAfter sigaltstack() with small size (%u bytes).\n", small_size);
+ setup_altstack(altstack, small_size, SUCCESS_EXPECTED);
+ validate_req_xcomp_perm(FAIL_EXPECTED);
+
+ /*
+ * Try setup_altstack() with a size derived from
+ * AT_MINSIGSTKSZ. It should be more than large enough
+ * and thus ARCH_REQ_XCOMP_PERM should succeed.
+ */
+ printf("\tAfter sigaltstack() with enough size (%u bytes).\n", enough_size);
+ setup_altstack(altstack, enough_size, SUCCESS_EXPECTED);
+ validate_req_xcomp_perm(SUCCESS_EXPECTED);
+
+ /*
+ * Try to coerce setup_altstack() to again accept a
+ * too-small altstack. This ensures that big-enough
+ * sigaltstacks can not shrink to a too-small value
+ * once XTILEDATA permission is established.
+ */
+ printf("\tThen, sigaltstack() with small size (%u bytes).\n", small_size);
+ setup_altstack(altstack, small_size, FAIL_EXPECTED);
+}
+
+static void test_dynamic_state(void)
+{
+ pid_t parent, child, grandchild;
+
+ parent = fork();
+ if (parent < 0) {
+ /* fork() failed */
+ fatal_error("fork");
+ } else if (parent > 0) {
+ int status;
+ /* fork() succeeded. Now in the parent. */
+
+ wait(&status);
+ if (!WIFEXITED(status) || WEXITSTATUS(status))
+ fatal_error("arch_prctl test parent exit");
+ return;
+ }
+ /* fork() succeeded. Now in the child . */
+
+ printf("[RUN]\tCheck ARCH_REQ_XCOMP_PERM around process fork() and sigaltack() test.\n");
+
+ printf("\tFork a child.\n");
+ child = fork();
+ if (child < 0) {
+ fatal_error("fork");
+ } else if (child > 0) {
+ int status;
+
+ wait(&status);
+ if (!WIFEXITED(status) || WEXITSTATUS(status))
+ fatal_error("arch_prctl test child exit");
+ _exit(0);
+ }
+
+ /*
+ * The permission request should fail without an
+ * XTILEDATA-compatible signal stack
+ */
+ printf("\tTest XCOMP_PERM at child.\n");
+ validate_xcomp_perm(FAIL_EXPECTED);
+
+ /*
+ * Set up an XTILEDATA-compatible signal stack and
+ * also obtain permission to populate XTILEDATA.
+ */
+ printf("\tTest dynamic sigaltstack at child:\n");
+ test_dynamic_sigaltstack();
+
+ /* Ensure that XTILEDATA can be populated. */
+ printf("\tTest XCOMP_PERM again at child.\n");
+ validate_xcomp_perm(SUCCESS_EXPECTED);
+
+ printf("\tFork a grandchild.\n");
+ grandchild = fork();
+ if (grandchild < 0) {
+ /* fork() failed */
+ fatal_error("fork");
+ } else if (!grandchild) {
+ /* fork() succeeded. Now in the (grand)child. */
+ printf("\tTest XCOMP_PERM at grandchild.\n");
+
+ /*
+ * Ensure that the grandchild inherited
+ * permission and a compatible sigaltstack:
+ */
+ validate_xcomp_perm(SUCCESS_EXPECTED);
+ } else {
+ int status;
+ /* fork() succeeded. Now in the parent. */
+
+ wait(&status);
+ if (!WIFEXITED(status) || WEXITSTATUS(status))
+ fatal_error("fork test grandchild");
+ }
+
+ _exit(0);
+}
+
+/*
+ * Save current register state and compare it to @xbuf1.'
+ *
+ * Returns false if @xbuf1 matches the registers.
+ * Returns true if @xbuf1 differs from the registers.
+ */
+static inline bool __validate_tiledata_regs(struct xsave_buffer *xbuf1)
+{
+ struct xsave_buffer *xbuf2;
+ int ret;
+
+ xbuf2 = alloc_xbuf();
+ if (!xbuf2)
+ fatal_error("failed to allocate XSAVE buffer\n");
+
+ xsave(xbuf2, XFEATURE_MASK_XTILEDATA);
+ ret = memcmp(&xbuf1->bytes[xtiledata.xbuf_offset],
+ &xbuf2->bytes[xtiledata.xbuf_offset],
+ xtiledata.size);
+
+ free(xbuf2);
+
+ if (ret == 0)
+ return false;
+ 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);
+
+ if (ret == 0)
+ fatal_error("TILEDATA registers did not change");
+}
+
+/* tiledata inheritance test */
+
+static void test_fork(void)
+{
+ pid_t child, grandchild;
+
+ child = fork();
+ if (child < 0) {
+ /* fork() failed */
+ fatal_error("fork");
+ } else if (child > 0) {
+ /* fork() succeeded. Now in the parent. */
+ int status;
+
+ wait(&status);
+ if (!WIFEXITED(status) || WEXITSTATUS(status))
+ fatal_error("fork test child");
+ return;
+ }
+ /* fork() succeeded. Now in the child. */
+ printf("[RUN]\tCheck tile data inheritance.\n\tBefore fork(), load tiledata\n");
+
+ load_rand_tiledata(stashed_xsave);
+
+ grandchild = fork();
+ if (grandchild < 0) {
+ /* fork() failed */
+ fatal_error("fork");
+ } else if (grandchild > 0) {
+ /* fork() succeeded. Still in the first child. */
+ int status;
+
+ wait(&status);
+ if (!WIFEXITED(status) || WEXITSTATUS(status))
+ fatal_error("fork test grand child");
+ _exit(0);
+ }
+ /* fork() succeeded. Now in the (grand)child. */
+
+ /*
+ * TILEDATA registers are not preserved across fork().
+ * Ensure that their value has changed:
+ */
+ validate_tiledata_regs_changed(stashed_xsave);
+
+ _exit(0);
+}
+
+int main(void)
+{
+ /* Check hardware availability at first */
+ check_cpuid_xsave();
+ check_cpuid_xtiledata();
+
+ init_stashed_xsave();
+ sethandler(SIGILL, handle_noperm, 0);
+
+ test_dynamic_state();
+
+ /* Request permission for the following tests */
+ req_xtiledata_perm();
+
+ test_fork();
+
+ clearhandler(SIGILL);
+ free_stashed_xsave();
+
+ return 0;
+}
diff -puN tools/testing/selftests/x86/Makefile~amx-selftest-1_3-selftest-x86-amx-Test-cases-for-the-AMX-state-management tools/testing/selftests/x86/Makefile
--- a/tools/testing/selftests/x86/Makefile~amx-selftest-1_3-selftest-x86-amx-Test-cases-for-the-AMX-state-management 2021-10-15 13:56:39.829901810 -0700
+++ b/tools/testing/selftests/x86/Makefile 2021-10-15 13:56:39.829901810 -0700
@@ -18,7 +18,7 @@ TARGETS_C_32BIT_ONLY := entry_from_vm86
test_FCMOV test_FCOMI test_FISTTP \
vdso_restorer
TARGETS_C_64BIT_ONLY := fsgsbase sysret_rip syscall_numbering \
- corrupt_xstate_header
+ corrupt_xstate_header amx
# Some selftests require 32bit support enabled also on 64bit systems
TARGETS_C_32BIT_NEEDED := ldt_gdt ptrace_syscall
_
