x86, fpu: Don't abuse has_fpu in __kernel_fpu_begin/end()
authorOleg Nesterov <oleg@redhat.com>
Thu, 15 Jan 2015 19:20:05 +0000 (20:20 +0100)
committerThomas Gleixner <tglx@linutronix.de>
Tue, 20 Jan 2015 12:53:07 +0000 (13:53 +0100)
commit33a3ebdc077fd85f1bf4d4586eea579b297461ae
treea3a6045efe0606f0dd0ae89df9f3db9cf7d84c06
parent14e153ef75eecae8fd0738ffb42120f4962a00cd
x86, fpu: Don't abuse has_fpu in __kernel_fpu_begin/end()

Now that we have in_kernel_fpu we can remove __thread_clear_has_fpu()
in __kernel_fpu_begin(). And this allows to replace the asymmetrical
and nontrivial use_eager_fpu + tsk_used_math check in kernel_fpu_end()
with the same __thread_has_fpu() check.

The logic becomes really simple; if _begin() does save() then _end()
needs restore(), this is controlled by __thread_has_fpu(). Otherwise
they do clts/stts unless use_eager_fpu().

Not only this makes begin/end symmetrical and imo more understandable,
potentially this allows to change irq_fpu_usable() to avoid all other
checks except "in_kernel_fpu".

Also, with this patch __kernel_fpu_end() does restore_fpu_checking()
and WARNs if it fails instead of math_state_restore(). I think this
looks better because we no longer need __thread_fpu_begin(), and it
would be better to report the failure in this case.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: matt.fleming@intel.com
Cc: bp@suse.de
Cc: pbonzini@redhat.com
Cc: luto@amacapital.net
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Suresh Siddha <sbsiddha@gmail.com>
Link: http://lkml.kernel.org/r/20150115192005.GC27332@redhat.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
arch/x86/kernel/i387.c