[PATCH v1] arm64: fix bug for reloading FPSIMD state after cpu power off
From: catalin.marinas@arm.com (Catalin Marinas)
Date: 2014-08-31 22:11:39
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On 31 Aug 2014, at 06:39, Leo Yan [off-list ref] 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.
quoted hunk ↗ jump to hunk
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). Catalin