[PATCH 3/3] x86, FPU: Do not use static_cpu_has before alternatives

Borislav Petkov
2013-04-29T14:04:37Z

From: Borislav Petkov <bp@suse.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@suse.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