arm64/fpsimd: Clear SME state in the target task when setting the VL

When setting SME vector lengths we clear TIF_SME to reenable SME traps,
doing a reallocation of the backing storage on next use. We do this using
clear_thread_flag() which operates on the current thread, meaning that when
setting the vector length via ptrace we may both not force traps for the
target task and force a spurious flush of any SME state that the tracing
task may have.

Clear the flag in the target task.

Fixes: e12310a ("arm64/sme: Implement ptrace support for streaming mode SVE registers")
Reported-by: David Spickett <[email protected]>
Signed-off-by: Mark Brown <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>

Author: broonie

arch/arm64/kernel/fpsimd.c

@@ -909,7 +909,7 @@ int vec_set_vector_length(struct task_struct *task, enum vec_type type,
 			 */
 			task->thread.svcr &= ~(SVCR_SM_MASK |
 					       SVCR_ZA_MASK);
-			clear_thread_flag(TIF_SME);
+			clear_tsk_thread_flag(task, TIF_SME);
 			free_sme = true;
 		}
 	}