3.2.55-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Linus Torvalds <torva...@linux-foundation.org>

commit 26bef1318adc1b3a530ecc807ef99346db2aa8b0 upstream.

Before we do an EMMS in the AMD FXSAVE information leak workaround we
need to clear any pending exceptions, otherwise we trap with a
floating-point exception inside this code.

Reported-by: halfdog <m...@halfdog.net>
Tested-by: Borislav Petkov <b...@suse.de>
Link: 
http://lkml.kernel.org/r/CA%2B55aFxQnY_PCG_n4=0w-VG=ylxl-yr7omxyy0wu2gcbaf3...@mail.gmail.com
Signed-off-by: H. Peter Anvin <h...@zytor.com>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
 arch/x86/kernel/traps.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -582,12 +582,13 @@ void __math_state_restore(struct task_st
        /* AMD K7/K8 CPUs don't save/restore FDP/FIP/FOP unless an exception
           is pending.  Clear the x87 state here by setting it to fixed
           values. safe_address is a random variable that should be in L1 */
-       alternative_input(
-               ASM_NOP8 ASM_NOP2,
-               "emms\n\t"              /* clear stack tags */
-               "fildl %P[addr]",       /* set F?P to defined value */
-               X86_FEATURE_FXSAVE_LEAK,
-               [addr] "m" (safe_address));
+       if (unlikely(static_cpu_has(X86_FEATURE_FXSAVE_LEAK))) {
+               asm volatile(
+                       "fnclex\n\t"
+                       "emms\n\t"
+                       "fildl %P[addr]"        /* set F?P to defined value */
+                       : : [addr] "m" (safe_address));
+       }
 
        /*
         * Paranoid restore. send a SIGSEGV if we fail to restore the state.

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