On 09/01/2014 06:11 AM, Catalin Marinas wrote:

On 31 Aug 2014, at 06:39, Leo Yan [off-list ref] wrote:

quoted

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

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(&current->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.

u are right, in some special cases (such like IKS, etc) a normal thread 
also may call cpu_suspend() function so that it will run here; i will 
commit another patch to reserve this part.

quoted

+		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.

quoted

		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).

Will reserve this part as well.

Thanks,
Leo Yan