linux-kernel - [tip:x86/fpu] x86, fpu: Use static_cpu_has

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Message-ID: <tip-5f8c4218148822fde6eebbeefc34bd0a6061e031@git.kernel.org>
Date:	Thu, 20 Jun 2013 17:52:02 -0700
From:	tip-bot for Borislav Petkov <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	tglx@...utronix.de, hpa@...ux.intel.com, bp@...e.de
Subject: [tip:x86/fpu] x86, fpu:
  Use static_cpu_has_safe before alternatives

Commit-ID:  5f8c4218148822fde6eebbeefc34bd0a6061e031
Gitweb:     http://git.kernel.org/tip/5f8c4218148822fde6eebbeefc34bd0a6061e031
Author:     Borislav Petkov <bp@...e.de>
AuthorDate: Sun, 9 Jun 2013 12:07:34 +0200
Committer:  H. Peter Anvin <hpa@...ux.intel.com>
CommitDate: Thu, 20 Jun 2013 17:38:22 -0700

x86, fpu: Use static_cpu_has_safe before alternatives

The call stack below shows how this happens: basically eager_fpu_init()
calls __thread_fpu_begin(current) which then does if (!use_eager_fpu()),
which, in turn, uses static_cpu_has.

And we're executing before alternatives so static_cpu_has doesn't work
there yet.

Use the safe variant in this path which becomes optimal after
alternatives have run.

WARNING: at arch/x86/kernel/cpu/common.c:1368 warn_pre_alternatives+0x1e/0x20()
You're using static_cpu_has before alternatives have run!
Modules linked in:
Pid: 0, comm: swapper Not tainted 3.9.0-rc8+ #1
Call Trace:
 warn_slowpath_common
 warn_slowpath_fmt
 ? fpu_finit
 warn_pre_alternatives
 eager_fpu_init
 fpu_init
 cpu_init
 trap_init
 start_kernel
 ? repair_env_string
 x86_64_start_reservations
 x86_64_start_kernel

Signed-off-by: Borislav Petkov <bp@...e.de>
Link: http://lkml.kernel.org/r/1370772454-6106-6-git-send-email-bp@alien8.de
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
---
 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 fb808d7..4d0bda7 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -343,7 +343,7 @@ static inline void __thread_fpu_end(struct task_struct *tsk)

 static inline void __thread_fpu_begin(struct task_struct *tsk)
 {
-	if (!use_eager_fpu())
+	if (!static_cpu_has_safe(X86_FEATURE_EAGER_FPU))
 		clts();
 	__thread_set_has_fpu(tsk);
 }
--
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