[PATCH]Fix boot hang in 3.11-rc1/2 because of bug in AMD errata check

[Torsten Kaiser <just.for.lkml@googlemail.com>]

cpu_has_amd_erratum() is buggy, because it uses the per-cpu cpu_info
before it is filled by smp_store_boot_cpu_info() / smp_store_cpu_info().

If early microcode loading is enabled its collect_cpu_info_amd_early() will
fill ->x86 and so the fallback to boot_cpu_data is not used.
But ->x86_vendor was not filled and is still 0 == X86_VENDOR_INTEL resulting in 
no errata fixes getting applied and my system hangs on boot.

Using cpu_info in cpu_has_amd_erratum() is wrong anyway: Its only caller
init_amd() will have a struct cpuinfo_x86 as parameter and the set_cpu_bug()
that is controlled by cpu_has_amd_erratum() also only uses that struct.

So pass the struct cpuinfo_x86 from init_amd() to cpu_has_amd_erratum() and
the broken fallback can be dropped.

I also turned the vendor check into an BUG_ON() because init_amd() can only
be used by AMD CPUs and if the current failure hadn't been silent this bug
would have been much more obvious.

Signed-off-by: Torsten Kaiser <just.for.lkml@googlemail.com>

--- a/arch/x86/kernel/cpu/amd.c	2013-07-22 06:33:10.027931005 +0200
+++ b/arch/x86/kernel/cpu/amd.c	2013-07-22 06:35:15.757931265 +0200
@@ -512,7 +512,7 @@ static void early_init_amd(struct cpuinf
 
 static const int amd_erratum_383[];
 static const int amd_erratum_400[];
-static bool cpu_has_amd_erratum(const int *erratum);
+static bool cpu_has_amd_erratum(struct cpuinfo_x86 *cpu, const int *erratum);
 
 static void init_amd(struct cpuinfo_x86 *c)
 {
@@ -729,11 +729,11 @@ static void init_amd(struct cpuinfo_x86
 		value &= ~(1ULL << 24);
 		wrmsrl_safe(MSR_AMD64_BU_CFG2, value);
 
-		if (cpu_has_amd_erratum(amd_erratum_383))
+		if (cpu_has_amd_erratum(c, amd_erratum_383))
 			set_cpu_bug(c, X86_BUG_AMD_TLB_MMATCH);
 	}
 
-	if (cpu_has_amd_erratum(amd_erratum_400))
+	if (cpu_has_amd_erratum(c, amd_erratum_400))
 		set_cpu_bug(c, X86_BUG_AMD_APIC_C1E);
 
 	rdmsr_safe(MSR_AMD64_PATCH_LEVEL, &c->microcode, &dummy);
@@ -878,22 +878,15 @@ static const int amd_erratum_400[] =
 static const int amd_erratum_383[] =
 	AMD_OSVW_ERRATUM(3, AMD_MODEL_RANGE(0x10, 0, 0, 0xff, 0xf));
 
-static bool cpu_has_amd_erratum(const int *erratum)
+
+static bool cpu_has_amd_erratum(struct cpuinfo_x86 *cpu, const int *erratum)
 {
-	struct cpuinfo_x86 *cpu = __this_cpu_ptr(&cpu_info);
 	int osvw_id = *erratum++;
 	u32 range;
 	u32 ms;
 
-	/*
-	 * If called early enough that current_cpu_data hasn't been initialized
-	 * yet, fall back to boot_cpu_data.
-	 */
-	if (cpu->x86 == 0)
-		cpu = &boot_cpu_data;
-
-	if (cpu->x86_vendor != X86_VENDOR_AMD)
-		return false;
+	/* Should never be called on non-AMD-CPUs */
+	BUG_ON(cpu->x86_vendor != X86_VENDOR_AMD);
 
 	if (osvw_id >= 0 && osvw_id < 65536 &&
 	    cpu_has(cpu, X86_FEATURE_OSVW)) {