1 files changed, 26 insertions, 4 deletions

diff --git a/include/asm-i386/i387.h b/include/asm-i386/i387.h
index 152d0baa576a..bc1d6edae1ed 100644
--- a/include/asm-i386/i387.h
+++ b/include/asm-i386/i387.h
@@ -13,6 +13,7 @@
 
 #include <linux/sched.h>
 #include <linux/init.h>
+#include <linux/kernel_stat.h>
 #include <asm/processor.h>
 #include <asm/sigcontext.h>
 #include <asm/user.h>
@@ -38,17 +39,38 @@ extern void init_fpu(struct task_struct *);
 extern void kernel_fpu_begin(void);
 #define kernel_fpu_end() do { stts(); preempt_enable(); } while(0)
 
+/* We need a safe address that is cheap to find and that is already
+   in L1 during context switch. The best choices are unfortunately
+   different for UP and SMP */
+#ifdef CONFIG_SMP
+#define safe_address (__per_cpu_offset[0])
+#else
+#define safe_address (kstat_cpu(0).cpustat.user)
+#endif
+
 /*
  * These must be called with preempt disabled
  */
 static inline void __save_init_fpu( struct task_struct *tsk )
 {
+        /* Use more nops than strictly needed in case the compiler
+           varies code */
         alternative_input(
-                "fnsave %1 ; fwait ;" GENERIC_NOP2,
-                "fxsave %1 ; fnclex",
+                "fnsave %[fx] ;fwait;" GENERIC_NOP8 GENERIC_NOP4,
+                "fxsave %[fx]\n"
+                "bt $7,%[fsw] ; jnc 1f ; fnclex\n1:",
                 X86_FEATURE_FXSR,
-                "m" (tsk->thread.i387.fxsave)
-                :"memory");
+                [fx] "m" (tsk->thread.i387.fxsave),
+                [fsw] "m" (tsk->thread.i387.fxsave.swd) : "memory");
+        /* 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(
+                GENERIC_NOP8 GENERIC_NOP2,
+                "emms\n\t"              /* clear stack tags */
+                "fildl %[addr]",        /* set F?P to defined value */
+                X86_FEATURE_FXSAVE_LEAK,
+                [addr] "m" (safe_address));
         task_thread_info(tsk)->status &= ~TS_USEDFPU;
 }