On 05/02/2016 10:19 AM, Yu-cheng Yu wrote:
> On Mon, May 02, 2016 at 09:43:47AM -0700, Dave Hansen wrote:
>>> If (fpu.fpstate_active == 0), then the task does not use FPU; we don't
>>> want to save these registers, right?
>>
>> No. It's possible to have fpstate_active=0 while fpregs_active=1. Such
>> a task uses the FPU, but just hasn't done an XSAVE* to save the register
>> content to the fpstate buffer.
>>
>> Note, this is just theoretical, and does not happen in this particular
>> call path today.
>
> What about...
>
> static int may_copy_fpregs_to_sigframe(void)
> {
> if (fpregs_active())
> return 1;
>
> WARN_ONCE(!current->thread.fpu.fpstate_active,
> "direct FPU save with no math use\n");
>
> if (boot_cpu_has(X86_FEATURE_XSAVES))
> return 1;
>
> return 0;
> }
I don't think that changes anything. We still have a check in there
that has no purpose. You've changed the ordering so that the specific
example that I pointed out no longer triggers it. But, the underlying
issue remains.
