On Fri, 2023-02-03 at 20:44 +0100, Borislav Petkov wrote:

quoted

I think we have to read it before we enable interrupts or use
fpregs_lock(). So reading it before saves disabling preemption
later.

So I'm a bit confused - there's that cond_local_irq_enable() which
will
enable interrupts if they were enabled before.

So if they were enabled before and you reenable them here, then that
current could be the wrong one if we schedule in between, right?

IOW, shouldn't those two lines be swapped so that it says:

        tsk = current;

        cond_local_irq_enable(regs);

and you can be sure that tsk is always the right current which caused
the #CP? Or am I way off again?

Since this path is only for exceptions coming from userspace, I think
it should be valid either way. It can't be during a task switch.
I can swap the lines if it looks odd, but unless I'm wrong about the
'current' validity I think it's negligibly better as is because it is
preemptible for as long as possible.