linux-kernel - [tip:x86/fpu] x86/fpu: Also check fpu_lazy_restore() when use_eager

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Date:	Thu, 19 Feb 2015 03:34:26 -0800
From:	tip-bot for Rik van Riel <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	tglx@...utronix.de, oleg@...hat.com, hpa@...or.com,
	mingo@...nel.org, torvalds@...ux-foundation.org, bp@...e.de,
	riel@...hat.com, linux-kernel@...r.kernel.org
Subject: [tip:x86/fpu] x86/fpu: Also check fpu_lazy_restore()
  when use_eager_fpu()

Commit-ID:  728e53fef429a0f3c9dda3587c3ccc57ad268b70
Gitweb:     http://git.kernel.org/tip/728e53fef429a0f3c9dda3587c3ccc57ad268b70
Author:     Rik van Riel <riel@...hat.com>
AuthorDate: Fri, 6 Feb 2015 15:02:05 -0500
Committer:  Borislav Petkov <bp@...e.de>
CommitDate: Thu, 19 Feb 2015 11:15:55 +0100

x86/fpu: Also check fpu_lazy_restore() when use_eager_fpu()

With Oleg's patch:

  33a3ebdc077f ("x86, fpu: Don't abuse has_fpu in __kernel_fpu_begin/end()")

kernel threads no longer have an FPU state even on systems with
use_eager_fpu().

That in turn means that a task may still have its FPU state
loaded in the FPU registers, if the task only got interrupted by
kernel threads from when it went to sleep, to when it woke up
again.

In that case, there is no need to restore the FPU state for
this task, since it is still in the registers.

The kernel can simply use the same logic to determine this as
is used for !use_eager_fpu() systems.

Signed-off-by: Rik van Riel <riel@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Link: http://lkml.kernel.org/r/1423252925-14451-9-git-send-email-riel@redhat.com
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/include/asm/fpu-internal.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
index e5f8f8e..19fb41c 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -458,7 +458,7 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta
 		task_disable_lazy_fpu_restore(old);
 		if (fpu.preload) {
 			new->thread.fpu_counter++;
-			if (!use_eager_fpu() && fpu_lazy_restore(new, cpu))
+			if (fpu_lazy_restore(new, cpu))
 				fpu.preload = 0;
 			else
 				prefetch(new->thread.fpu.state);
--
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