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: e12310a0d30f ("arm64/sme: Implement ptrace support for streaming mode SVE registers") Reported-by: David Spickett David.Spickett@arm.com Signed-off-by: Mark Brown broonie@kernel.org Cc: stable@vger.kernel.org --- arch/arm64/kernel/fpsimd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index 520b681a07bb..a61a1fd6492d 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/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; } }

--- base-commit: 5d0c230f1de8c7515b6567d9afba1f196fb4e2f4 change-id: 20230802-arm64-fix-ptrace-tif-sme-0bfd94c8266d

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