On 6 May 2014 18:08, Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
> On Thu, May 01, 2014 at 04:49:35PM +0100, Ard Biesheuvel wrote:
>> @@ -153,12 +252,11 @@ static int fpsimd_cpu_pm_notifier(struct notifier_block *self,
>> {
>> switch (cmd) {
>> case CPU_PM_ENTER:
>> - if (current->mm)
>> + if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
>> fpsimd_save_state(¤t->thread.fpsimd_state);
>> break;
>> case CPU_PM_EXIT:
>> - if (current->mm)
>> - fpsimd_load_state(¤t->thread.fpsimd_state);
>> + set_thread_flag(TIF_FOREIGN_FPSTATE);
>
> I think we could enter a PM state on a kernel thread (idle), so we
> should preserve the current->mm check as well.
>
OK
>> break;
>> case CPU_PM_ENTER_FAILED:
>> default:
>> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
>> index 06448a77ff53..882f01774365 100644
>> --- a/arch/arm64/kernel/signal.c
>> +++ b/arch/arm64/kernel/signal.c
>> @@ -413,4 +413,8 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
>> clear_thread_flag(TIF_NOTIFY_RESUME);
>> tracehook_notify_resume(regs);
>> }
>> +
>> + if (thread_flags & _TIF_FOREIGN_FPSTATE)
>> + fpsimd_restore_current_state();
>
> I think this should be safe. Even if we get preempted here, ret_to_user
> would loop over TI_FLAGS with interrupts disabled until no work pending.
>
I don't follow. Do you think I should change something here?
Anyway, inside fpsimd_restore_current_state() the TIF_FOREIGN_FPSTATE
is checked again, but this time with preemption disabled.
--
Ard.
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