linux-kernel - Re: [PATCH] Make math_state_restore() save and restore the interrupt flag

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Message-ID: <CALmL7E_ijZStgyxj4Gnn69sEF-kv+eBE64+J7OBfn-K4cbBmJg@mail.gmail.com>
Date:	Sat, 1 Feb 2014 17:35:13 -0800
From:	Suresh Siddha <sbsiddha@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nate Eldredge <nate@...tsmathematics.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	stable <stable@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Maarten Baert <maarten-baert@...mail.com>,
	Jan Kara <jack@...e.cz>, George Spelvin <linux@...izon.com>,
	Pekka Riikonen <priikone@....fi>
Subject: Re: [PATCH] Make math_state_restore() save and restore the interrupt flag

On Sat, Feb 1, 2014 at 5:26 PM, H. Peter Anvin <hpa@...or.com> wrote:
> Even "b" does that, no?

oh right. It needs an else. only for non-eager fpu case we should do stts()

  void __kernel_fpu_end(void)
  {
          if (use_eager_fpu()) {
                  struct task_struct *me = current;

                  if (tsk_used_math(me) && likely(!restore_fpu_checking(
me)))
                          return;
          } else
                  stts();
  }

thanks,
suresh

> "a" should be fine as long as we don't ever use
> those features in the kernel, even under kernel_fpu_begin/end().
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