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Diffstat (limited to 'arch/x86/kernel/cpu/common.c')
-rw-r--r--arch/x86/kernel/cpu/common.c31
1 files changed, 19 insertions, 12 deletions
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index f1af7185191..25581dcb280 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -124,18 +124,25 @@ static inline int flag_is_changeable_p(u32 flag)
{
u32 f1, f2;
- asm("pushfl\n\t"
- "pushfl\n\t"
- "popl %0\n\t"
- "movl %0,%1\n\t"
- "xorl %2,%0\n\t"
- "pushl %0\n\t"
- "popfl\n\t"
- "pushfl\n\t"
- "popl %0\n\t"
- "popfl\n\t"
- : "=&r" (f1), "=&r" (f2)
- : "ir" (flag));
+ /*
+ * Cyrix and IDT cpus allow disabling of CPUID
+ * so the code below may return different results
+ * when it is executed before and after enabling
+ * the CPUID. Add "volatile" to not allow gcc to
+ * optimize the subsequent calls to this function.
+ */
+ asm volatile ("pushfl\n\t"
+ "pushfl\n\t"
+ "popl %0\n\t"
+ "movl %0,%1\n\t"
+ "xorl %2,%0\n\t"
+ "pushl %0\n\t"
+ "popfl\n\t"
+ "pushfl\n\t"
+ "popl %0\n\t"
+ "popfl\n\t"
+ : "=&r" (f1), "=&r" (f2)
+ : "ir" (flag));
return ((f1^f2) & flag) != 0;
}