1 files changed, 36 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/common_64.c b/arch/x86/kernel/cpu/common_64.c
index 6f9b8924bdc0..af569a964e74 100644
--- a/arch/x86/kernel/cpu/common_64.c
+++ b/arch/x86/kernel/cpu/common_64.c
@@ -18,6 +18,7 @@
 #include <asm/mtrr.h>
 #include <asm/mce.h>
 #include <asm/pat.h>
+#include <asm/asm.h>
 #include <asm/numa.h>
 #ifdef CONFIG_X86_LOCAL_APIC
 #include <asm/mpspec.h>
@@ -215,6 +216,39 @@ static void __init early_cpu_support_print(void)
         }
 }
 
+/*
+ * The NOPL instruction is supposed to exist on all CPUs with
+ * 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.
+ *
+ * Note: no 64-bit chip is known to lack these, but put the code here
+ * for consistency with 32 bits, and to make it utterly trivial to
+ * diagnose the problem should it ever surface.
+ */
+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 early_identify_cpu(struct cpuinfo_x86 *c);
 
 void __init early_cpu_init(void)
@@ -313,6 +347,8 @@ static void __cpuinit early_identify_cpu(struct cpuinfo_x86 *c)
                 c->x86_phys_bits = eax & 0xff;
         }
 
+        detect_nopl(c);
+
         if (c->x86_vendor != X86_VENDOR_UNKNOWN &&
             cpu_devs[c->x86_vendor]->c_early_init)
                 cpu_devs[c->x86_vendor]->c_early_init(c);