Re: [PATCH 04/10] x86/xsaves: Introduce a new check that allows correct xstates copy from kernel to user directly

[Yu-cheng Yu]

On Mon, Feb 22, 2016 at 02:42:54PM -0800, Andy Lutomirski wrote:
> > +static int should_save_registers_directly(void)
> 
> I don't like the name of this function because:
> 
> > +{
> > +       /*
> > +        * In signal handling path, the kernel already checks if
> > +        * FPU instructions have been used before it calls
> > +        * copy_fpstate_to_sigframe(). We check this here again
> > +        * to detect any potential mis-use and saving invalid
> > +        * register values directly to a signal frame.
> > +        */
> > +       WARN_ONCE(!current->thread.fpu.fpstate_active,
> > +                 "direct FPU save with no math use\n");
> 
> ... Here "direct" seems to mean that we're asking whether to directly save ...
> 
> > +
> > +       /*
> > +        * In the case that we are using a compacted kernel
> > +        * xsave area, we can not copy the thread.fpu.state
> > +        * directly to userspace and *must* save it from the
> > +        * registers directly.
> > +        */
> 
> ... and here "directly" means *both* copying directly to userspace and
> saving using xsave directly.
> 
> So can you rename it to something with an obvious meaning like
> "may_memcpy_fpu_regs" or similar?

This function determines whether the kernel should do
copy_fpregs_to_sigframe(). Perhaps we can re-name it to
may_copy_fpregs_to_sigframe()?

--Yu-cheng