linux-kernel - [PATCH 3/3] x86, FPU: Do not use static_cpu

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Date:	Mon, 29 Apr 2013 16:04:22 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...e.de>
Subject: [PATCH 3/3] x86, FPU: Do not use static_cpu_has before alternatives

From: Borislav Petkov <bp@...e.de>

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.

However, I don't want to cause the penalty of not using static_cpu_has
to all callers of use_eager_fpu() which are a bunch spread around the
tree so let's add the change only to __thread_fpu_begin() - it is still
on the context switch path but we can at least keep the static_cpu_has
call in the rest of the use_eager_fpu() callsites.

WARNING: at arch/x86/kernel/cpu/common.c:1368 warn_pre_alternatives+0x1e/0x20()
Hardware name: 2320CTO
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>
---
 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 fb808d71cd70..0e34793aafd4 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 (!cpu_has_eager_fpu)
 		clts();
 	__thread_set_has_fpu(tsk);
 }
-- 
1.8.3.rc0

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