4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Breno Leitao <leitao@xxxxxxxxxx> commit 1195892c091a15cc862f4e202482a36adc924e12 upstream. Currently tsk->thread->load_vec and load_fp are not initialized during task creation, which can lead to garbage values in these variables (non-zero values). These variables will be checked later in restore_math() to validate if the FP and vector registers are being utilized. Since these values might be non-zero, the restore_math() will continue to save the FP and vectors even if they were never utilized by the userspace application. load_fp and load_vec counters will then overflow (they wrap at 255) and the FP and Altivec will be finally disabled, but before that condition is reached (counter overflow) several context switches will have restored FP and vector registers without need, causing a performance degradation. Fixes: 70fe3d980f5f ("powerpc: Restore FPU/VEC/VSX if previously used") Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx> Signed-off-by: Gustavo Romero <gusbromero@xxxxxxxxx> Acked-by: Anton Blanchard <anton@xxxxxxxxx> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/powerpc/kernel/process.c | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1659,6 +1659,7 @@ void start_thread(struct pt_regs *regs, #ifdef CONFIG_VSX current->thread.used_vsr = 0; #endif + current->thread.load_fp = 0; memset(¤t->thread.fp_state, 0, sizeof(current->thread.fp_state)); current->thread.fp_save_area = NULL; #ifdef CONFIG_ALTIVEC @@ -1667,6 +1668,7 @@ void start_thread(struct pt_regs *regs, current->thread.vr_save_area = NULL; current->thread.vrsave = 0; current->thread.used_vr = 0; + current->thread.load_vec = 0; #endif /* CONFIG_ALTIVEC */ #ifdef CONFIG_SPE memset(current->thread.evr, 0, sizeof(current->thread.evr));