1 files changed, 27 insertions, 3 deletions

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 3eb338f14386..94289d126993 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -269,6 +269,7 @@ static void sve_free(struct task_struct *task)
  */
 static void task_fpsimd_load(void)
 {
+	WARN_ON(!system_supports_fpsimd());
 	WARN_ON(!have_cpu_fpsimd_context());
 
 	if (system_supports_sve() && test_thread_flag(TIF_SVE))
@@ -289,6 +290,7 @@ static void fpsimd_save(void)
 		this_cpu_ptr(&fpsimd_last_state);
 	/* set by fpsimd_bind_task_to_cpu() or fpsimd_bind_state_to_cpu() */
 
+	WARN_ON(!system_supports_fpsimd());
 	WARN_ON(!have_cpu_fpsimd_context());
 
 	if (!test_thread_flag(TIF_FOREIGN_FPSTATE)) {
@@ -1092,6 +1094,7 @@ void fpsimd_bind_task_to_cpu(void)
 	struct fpsimd_last_state_struct *last =
 		this_cpu_ptr(&fpsimd_last_state);
 
+	WARN_ON(!system_supports_fpsimd());
 	last->st = &current->thread.uw.fpsimd_state;
 	last->sve_state = current->thread.sve_state;
 	last->sve_vl = current->thread.sve_vl;
@@ -1114,6 +1117,7 @@ void fpsimd_bind_state_to_cpu(struct user_fpsimd_state *st, void *sve_state,
 	struct fpsimd_last_state_struct *last =
 		this_cpu_ptr(&fpsimd_last_state);
 
+	WARN_ON(!system_supports_fpsimd());
 	WARN_ON(!in_softirq() && !irqs_disabled());
 
 	last->st = st;
@@ -1128,8 +1132,19 @@ void fpsimd_bind_state_to_cpu(struct user_fpsimd_state *st, void *sve_state,
  */
 void fpsimd_restore_current_state(void)
 {
-	if (!system_supports_fpsimd())
+	/*
+	 * For the tasks that were created before we detected the absence of
+	 * FP/SIMD, the TIF_FOREIGN_FPSTATE could be set via fpsimd_thread_switch(),
+	 * e.g, init. This could be then inherited by the children processes.
+	 * If we later detect that the system doesn't support FP/SIMD,
+	 * we must clear the flag for  all the tasks to indicate that the
+	 * FPSTATE is clean (as we can't have one) to avoid looping for ever in
+	 * do_notify_resume().
+	 */
+	if (!system_supports_fpsimd()) {
+		clear_thread_flag(TIF_FOREIGN_FPSTATE);
 		return;
+	}
 
 	get_cpu_fpsimd_context();
 
@@ -1148,7 +1163,7 @@ void fpsimd_restore_current_state(void)
  */
 void fpsimd_update_current_state(struct user_fpsimd_state const *state)
 {
-	if (!system_supports_fpsimd())
+	if (WARN_ON(!system_supports_fpsimd()))
 		return;
 
 	get_cpu_fpsimd_context();
@@ -1179,7 +1194,13 @@ void fpsimd_update_current_state(struct user_fpsimd_state const *state)
 void fpsimd_flush_task_state(struct task_struct *t)
 {
 	t->thread.fpsimd_cpu = NR_CPUS;
-
+	/*
+	 * If we don't support fpsimd, bail out after we have
+	 * reset the fpsimd_cpu for this task and clear the
+	 * FPSTATE.
+	 */
+	if (!system_supports_fpsimd())
+		return;
 	barrier();
 	set_tsk_thread_flag(t, TIF_FOREIGN_FPSTATE);
 
@@ -1193,6 +1214,7 @@ void fpsimd_flush_task_state(struct task_struct *t)
  */
 static void fpsimd_flush_cpu_state(void)
 {
+	WARN_ON(!system_supports_fpsimd());
 	__this_cpu_write(fpsimd_last_state.st, NULL);
 	set_thread_flag(TIF_FOREIGN_FPSTATE);
 }
@@ -1203,6 +1225,8 @@ static void fpsimd_flush_cpu_state(void)
  */
 void fpsimd_save_and_flush_cpu_state(void)
 {
+	if (!system_supports_fpsimd())
+		return;
 	WARN_ON(preemptible());
 	__get_cpu_fpsimd_context();
 	fpsimd_save();