x86: completely disable NOPL on 32 bits
H. Peter Anvin [Tue, 16 Sep 2008 16:29:40 +0000 (09:29 -0700)]
Completely disable NOPL on 32 bits.  It turns out that Microsoft
Virtual PC is so broken it can't even reliably *fail* in the presence
of NOPL.

This leaves the infrastructure in place but disables it
unconditionally.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/kernel/cpu/common.c

index 8aab851..4e456bd 100644 (file)
@@ -344,31 +344,15 @@ static void __init early_cpu_detect(void)
 
 /*
  * The NOPL instruction is supposed to exist on all CPUs with
- * family >= 6, unfortunately, that's not true in practice because
+ * family >= 6; unfortunately, that's not true in practice because
  * of early VIA chips and (more importantly) broken virtualizers that
- * are not easy to detect.  Hence, probe for it based on first
- * principles.
+ * are not easy to detect.  In the latter case it doesn't even *fail*
+ * reliably, so probing for it doesn't even work.  Disable it completely
+ * unless we can find a reliable way to detect all the broken cases.
  */
 static void __cpuinit detect_nopl(struct cpuinfo_x86 *c)
 {
-       const u32 nopl_signature = 0x888c53b1; /* Random number */
-       u32 has_nopl = nopl_signature;
-
        clear_cpu_cap(c, X86_FEATURE_NOPL);
-       if (c->x86 >= 6) {
-               asm volatile("\n"
-                            "1:      .byte 0x0f,0x1f,0xc0\n" /* nopl %eax */
-                            "2:\n"
-                            "        .section .fixup,\"ax\"\n"
-                            "3:      xor %0,%0\n"
-                            "        jmp 2b\n"
-                            "        .previous\n"
-                            _ASM_EXTABLE(1b,3b)
-                            : "+a" (has_nopl));
-
-               if (has_nopl == nopl_signature)
-                       set_cpu_cap(c, X86_FEATURE_NOPL);
-       }
 }
 
 static void __cpuinit generic_identify(struct cpuinfo_x86 *c)