arm64/sme: Don't flush SVE register state when allocating SME storage

Currently when taking a SME access trap we allocate storage for the SVE
register state in order to be able to handle storage of streaming mode SVE.
Due to the original usage in a purely SVE context the SVE register state
allocation this also flushes the register state for SVE if storage was
already allocated but in the SME context this is not desirable. For a SME
access trap to be taken the task must not be in streaming mode so either
there already is SVE register state present for regular SVE mode which would
be corrupted or the task does not have TIF_SVE and the flush is redundant.

Fix this by adding a flag to sve_alloc() indicating if we are in a SVE
context and need to flush the state. Freshly allocated storage is always
zeroed either way.

Fixes: 8bd7f91c ("arm64/sme: Implement traps and syscall handling for SME")
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220817182324.638214-4-broonie@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/fpsimd.h

@@ -153,7 +153,7 @@ struct vl_info {
 
 #ifdef CONFIG_ARM64_SVE
 
-extern void sve_alloc(struct task_struct *task);
+extern void sve_alloc(struct task_struct *task, bool flush);
 extern void fpsimd_release_task(struct task_struct *task);
 extern void fpsimd_sync_to_sve(struct task_struct *task);
 extern void fpsimd_force_sync_to_sve(struct task_struct *task);
@@ -256,7 +256,7 @@ size_t sve_state_size(struct task_struct const *task);
 
 #else /* ! CONFIG_ARM64_SVE */
 
-static inline void sve_alloc(struct task_struct *task) { }
+static inline void sve_alloc(struct task_struct *task, bool flush) { }
 static inline void fpsimd_release_task(struct task_struct *task) { }
 static inline void sve_sync_to_fpsimd(struct task_struct *task) { }
 static inline void sve_sync_from_fpsimd_zeropad(struct task_struct *task) { }

arch/arm64/kernel/fpsimd.c

@@ -715,10 +715,12 @@ size_t sve_state_size(struct task_struct const *task)
  * do_sve_acc() case, there is no ABI requirement to hide stale data
  * written previously be task.
  */
-void sve_alloc(struct task_struct *task)
+void sve_alloc(struct task_struct *task, bool flush)
 {
 	if (task->thread.sve_state) {
-		memset(task->thread.sve_state, 0, sve_state_size(task));
+		if (flush)
+			memset(task->thread.sve_state, 0,
+			       sve_state_size(task));
 		return;
 	}
 
@@ -1388,7 +1390,7 @@ void do_sve_acc(unsigned long esr, struct pt_regs *regs)
 		return;
 	}
 
-	sve_alloc(current);
+	sve_alloc(current, true);
 	if (!current->thread.sve_state) {
 		force_sig(SIGKILL);
 		return;
@@ -1439,7 +1441,7 @@ void do_sme_acc(unsigned long esr, struct pt_regs *regs)
 		return;
 	}
 
-	sve_alloc(current);
+	sve_alloc(current, false);
 	sme_alloc(current);
 	if (!current->thread.sve_state || !current->thread.za_state) {
 		force_sig(SIGKILL);

arch/arm64/kernel/ptrace.c

@@ -882,7 +882,7 @@ static int sve_set_common(struct task_struct *target,
 		 * state and ensure there's storage.
 		 */
 		if (target->thread.svcr != old_svcr)
-			sve_alloc(target);
+			sve_alloc(target, true);
 	}
 
 	/* Registers: FPSIMD-only case */
@@ -912,7 +912,7 @@ static int sve_set_common(struct task_struct *target,
 		goto out;
 	}
 
-	sve_alloc(target);
+	sve_alloc(target, true);
 	if (!target->thread.sve_state) {
 		ret = -ENOMEM;
 		clear_tsk_thread_flag(target, TIF_SVE);
@@ -1082,7 +1082,7 @@ static int za_set(struct task_struct *target,
 
 	/* Ensure there is some SVE storage for streaming mode */
 	if (!target->thread.sve_state) {
-		sve_alloc(target);
+		sve_alloc(target, false);
 		if (!target->thread.sve_state) {
 			clear_thread_flag(TIF_SME);
 			ret = -ENOMEM;

arch/arm64/kernel/signal.c

@@ -310,7 +310,7 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user)
 	fpsimd_flush_task_state(current);
 	/* From now, fpsimd_thread_switch() won't touch thread.sve_state */
 
-	sve_alloc(current);
+	sve_alloc(current, true);
 	if (!current->thread.sve_state) {
 		clear_thread_flag(TIF_SVE);
 		return -ENOMEM;