i386: Fix perfctr watchdog on core duo

Fix the NMI watchdog on Intel CoreDuo processor where the kernel would
get stuck during boot.  The issue is related to errata AE49, where the
PERFEVTSEL1 counter does not have a working enable bit.  Thus it is not
possible to use it for NMI.

The patch creates a dedicated wd_ops for CoreDuo which falls back to
using PERFEVTSEL0.  The other Intel processors supporting the
architectural PMU will keep on using PERFEVTSEL1 as this allows other
subsystems, such as perfmon, to use PERFEVTSEL0 for PEBS monitoring in
particular.  Bug initially reported by Daniel Walker.

AK: Added comments

Signed-off-by: Stephane Eranian <eranian@hpl.hp.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/i386/kernel/cpu/perfctr-watchdog.c

@@ -263,8 +263,8 @@ static int setup_k7_watchdog(unsigned nmi_hz)
 	unsigned int evntsel;
 	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);
 
-	perfctr_msr = MSR_K7_PERFCTR0;
-	evntsel_msr = MSR_K7_EVNTSEL0;
+	perfctr_msr = wd_ops->perfctr;
+	evntsel_msr = wd_ops->evntsel;
 
 	wrmsrl(perfctr_msr, 0UL);
 
@@ -343,8 +343,8 @@ static int setup_p6_watchdog(unsigned nmi_hz)
 	unsigned int evntsel;
 	struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);
 
-	perfctr_msr = MSR_P6_PERFCTR0;
-	evntsel_msr = MSR_P6_EVNTSEL0;
+	perfctr_msr = wd_ops->perfctr;
+	evntsel_msr = wd_ops->evntsel;
 
 	/* KVM doesn't implement this MSR */
 	if (wrmsr_safe(perfctr_msr, 0, 0) < 0)
@@ -569,8 +569,8 @@ static int setup_intel_arch_watchdog(unsigned nmi_hz)
 	    (ebx & ARCH_PERFMON_UNHALTED_CORE_CYCLES_PRESENT))
 		return 0;
 
-	perfctr_msr = MSR_ARCH_PERFMON_PERFCTR1;
-	evntsel_msr = MSR_ARCH_PERFMON_EVENTSEL1;
+	perfctr_msr = wd_ops->perfctr;
+	evntsel_msr = wd_ops->evntsel;
 
 	wrmsrl(perfctr_msr, 0UL);
 
@@ -605,6 +605,16 @@ static struct wd_ops intel_arch_wd_ops = {
 	.evntsel = MSR_ARCH_PERFMON_EVENTSEL1,
 };
 
+static struct wd_ops coreduo_wd_ops = {
+	.reserve = single_msr_reserve,
+	.unreserve = single_msr_unreserve,
+	.setup = setup_intel_arch_watchdog,
+	.rearm = p6_rearm,
+	.stop = single_msr_stop_watchdog,
+	.perfctr = MSR_ARCH_PERFMON_PERFCTR0,
+	.evntsel = MSR_ARCH_PERFMON_EVENTSEL0,
+};
+
 static void probe_nmi_watchdog(void)
 {
 	switch (boot_cpu_data.x86_vendor) {
@@ -615,6 +625,12 @@ static void probe_nmi_watchdog(void)
 		wd_ops = &k7_wd_ops;
 		break;
 	case X86_VENDOR_INTEL:
+		/* Work around Core Duo (Yonah) errata AE49 where perfctr1
+		   doesn't have a working enable bit. */
+		if (boot_cpu_data.x86 == 6 && boot_cpu_data.x86_model == 14) {
+			wd_ops = &coreduo_wd_ops;
+			break;
+		}
 		if (cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON)) {
 			wd_ops = &intel_arch_wd_ops;
 			break;