Messages in this thread | | | Subject | Re: [PATCH v1] arm64: fix bug for reloading FPSIMD state after cpu power off | From | Catalin Marinas <> | Date | Sun, 31 Aug 2014 23:11:29 +0100 |
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On 31 Aug 2014, at 06:39, Leo Yan <leoy@marvell.com> wrote: > Now arm64 defers reloading FPSIMD state, but this optimization also > introduces the bug after cpu resume back from low power mode.
You are right, I can see a bug here.
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c > index ad8aebb..4caef93 100644 > --- a/arch/arm64/kernel/fpsimd.c > +++ b/arch/arm64/kernel/fpsimd.c > @@ -268,13 +268,9 @@ static int fpsimd_cpu_pm_notifier(struct notifier_block *self, > { > switch (cmd) { > case CPU_PM_ENTER: > - if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE)) > - fpsimd_save_state(¤t->thread.fpsimd_state);
That’s needed if we enter a low power state directly from a task with a valid mm (user). I’m not sure that’s possible, but just in case.
> + this_cpu_write(fpsimd_last_state, NULL);
That’s correct. In most cases, we enter low power state from the idle thread which does not have an mm, so the CPU_PM_EXIT case wouldn’t set a TIF_FOREIGN_FPSTATE, so thread switching would not detect the change.
> break; > case CPU_PM_EXIT: > - if (current->mm) > - set_thread_flag(TIF_FOREIGN_FPSTATE);
See above for why this may still be needed (it case it returns to user directly without fpsimd_thread_switch() to detect fpsimd_last_state).
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