3 files changed, 21 insertions, 7 deletions

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 75c37b1c55aa..087c05aa960e 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1285,9 +1285,9 @@ void fpsimd_release_task(struct task_struct *dead_task)
  * the interest of testability and predictability, the architecture
  * guarantees that when ZA is enabled it will be zeroed.
  */
-void sme_alloc(struct task_struct *task)
+void sme_alloc(struct task_struct *task, bool flush)
 {
-	if (task->thread.sme_state) {
+	if (task->thread.sme_state && flush) {
 		memset(task->thread.sme_state, 0, sme_state_size(task));
 		return;
 	}
@@ -1515,7 +1515,7 @@ void do_sme_acc(unsigned long esr, struct pt_regs *regs)
 	}
 
 	sve_alloc(current, false);
-	sme_alloc(current);
+	sme_alloc(current, true);
 	if (!current->thread.sve_state || !current->thread.sme_state) {
 		force_sig(SIGKILL);
 		return;
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 5b9b4305248b..187aa2b175b4 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -881,6 +881,13 @@ static int sve_set_common(struct task_struct *target,
 			break;
 		case ARM64_VEC_SME:
 			target->thread.svcr |= SVCR_SM_MASK;
+
+			/*
+			 * Disable traps and ensure there is SME storage but
+			 * preserve any currently set values in ZA/ZT.
+			 */
+			sme_alloc(target, false);
+			set_tsk_thread_flag(target, TIF_SME);
 			break;
 		default:
 			WARN_ON_ONCE(1);
@@ -1100,7 +1107,7 @@ static int za_set(struct task_struct *target,
 	}
 
 	/* Allocate/reinit ZA storage */
-	sme_alloc(target);
+	sme_alloc(target, true);
 	if (!target->thread.sme_state) {
 		ret = -ENOMEM;
 		goto out;
@@ -1170,8 +1177,13 @@ static int zt_set(struct task_struct *target,
 	if (!system_supports_sme2())
 		return -EINVAL;
 
+	/* Ensure SVE storage in case this is first use of SME */
+	sve_alloc(target, false);
+	if (!target->thread.sve_state)
+		return -ENOMEM;
+
 	if (!thread_za_enabled(&target->thread)) {
-		sme_alloc(target);
+		sme_alloc(target, true);
 		if (!target->thread.sme_state)
 			return -ENOMEM;
 	}
@@ -1179,8 +1191,10 @@ static int zt_set(struct task_struct *target,
 	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
 				 thread_zt_state(&target->thread),
 				 0, ZT_SIG_REG_BYTES);
-	if (ret == 0)
+	if (ret == 0) {
 		target->thread.svcr |= SVCR_ZA_MASK;
+		set_tsk_thread_flag(target, TIF_SME);
+	}
 
 	fpsimd_flush_task_state(target);
 
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index e304f7ebec2a..c7ebe744c64e 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -475,7 +475,7 @@ static int restore_za_context(struct user_ctxs *user)
 	fpsimd_flush_task_state(current);
 	/* From now, fpsimd_thread_switch() won't touch thread.sve_state */
 
-	sme_alloc(current);
+	sme_alloc(current, true);
 	if (!current->thread.sme_state) {
 		current->thread.svcr &= ~SVCR_ZA_MASK;
 		clear_thread_flag(TIF_SME);