Merge /spare/repo/linux-2.6/
[pandora-kernel.git] / arch / x86_64 / kernel / process.c
index 1d91271..7577f9d 100644 (file)
@@ -481,6 +481,33 @@ out:
        return err;
 }
 
+/*
+ * This function selects if the context switch from prev to next
+ * has to tweak the TSC disable bit in the cr4.
+ */
+static inline void disable_tsc(struct task_struct *prev_p,
+                              struct task_struct *next_p)
+{
+       struct thread_info *prev, *next;
+
+       /*
+        * gcc should eliminate the ->thread_info dereference if
+        * has_secure_computing returns 0 at compile time (SECCOMP=n).
+        */
+       prev = prev_p->thread_info;
+       next = next_p->thread_info;
+
+       if (has_secure_computing(prev) || has_secure_computing(next)) {
+               /* slow path here */
+               if (has_secure_computing(prev) &&
+                   !has_secure_computing(next)) {
+                       write_cr4(read_cr4() & ~X86_CR4_TSD);
+               } else if (!has_secure_computing(prev) &&
+                          has_secure_computing(next))
+                       write_cr4(read_cr4() | X86_CR4_TSD);
+       }
+}
+
 /*
  * This special macro can be used to load a debugging register
  */
@@ -599,6 +626,8 @@ struct task_struct *__switch_to(struct task_struct *prev_p, struct task_struct *
                }
        }
 
+       disable_tsc(prev_p, next_p);
+
        return prev_p;
 }