Re: [PATCH] perf,x86,p6: Add userspace RDPMC quirk for P6

[Peter Zijlstra]

On Wed, Feb 05, 2014 at 08:20:12PM +0100, Peter Zijlstra wrote:
> On Wed, Feb 05, 2014 at 02:16:43PM -0500, Vince Weaver wrote:
> > On Wed, 5 Feb 2014, Peter Zijlstra wrote:
> > 
> > > P6 class machines can die hard when PCE gets enabled due to CPU
> > > errata. The safe way it so disable it by default and keep it disabled.
> > > 
> > > See errata 26:
> > 
> > so you take an errata applicable to a subset of Pentium Pro steppings and 
> > apply it to the whole p6 line (which includes the whole way up to Pentium 
> > III)?
> > 
> > Or am I missing something in the documentation you link to?
> 
> I forgot it went all the way to P-III, let me try and find the other
> erratas.

OK, Just checked the P-II errata and its not there anymore, so I suppose
only Family 6 model 1 should have this quirk.

Updated patch below.

---
Subject: perf,x86,p6: Add userspace RDPMC quirk for PPro
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Wed Feb 5 11:17:46 CET 2014

PPro machines can die hard when PCE gets enabled due to CPU errata. The
safe way it so disable it by default and keep it disabled.

See errata 26:

http://download.intel.com/design/archives/processors/pro/docs/24268935.pdf

Cc: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
Reported-by: Mark Davies <junk@xxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-jnbn0qpt3t7ogk4c2q79yq90@xxxxxxxxxxxxxx
---
 arch/x86/kernel/cpu/perf_event.c    |    6 +++++-
 arch/x86/kernel/cpu/perf_event.h    |    1 +
 arch/x86/kernel/cpu/perf_event_p6.c |   35 +++++++++++++++++++++++++----------
 3 files changed, 31 insertions(+), 11 deletions(-)

--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1521,6 +1521,8 @@ static int __init init_hw_perf_events(vo
 
 	pr_cont("%s PMU driver.\n", x86_pmu.name);
 
+	x86_pmu.attr_rdpmc = 1; /* enable userspace RDPMC usage by default */
+
 	for (quirk = x86_pmu.quirks; quirk; quirk = quirk->next)
 		quirk->func();
 
@@ -1534,7 +1536,6 @@ static int __init init_hw_perf_events(vo
 		__EVENT_CONSTRAINT(0, (1ULL << x86_pmu.num_counters) - 1,
 				   0, x86_pmu.num_counters, 0, 0);
 
-	x86_pmu.attr_rdpmc = 1; /* enable userspace RDPMC usage by default */
 	x86_pmu_format_group.attrs = x86_pmu.format_attrs;
 
 	if (x86_pmu.event_attrs)
@@ -1820,6 +1821,9 @@ static ssize_t set_attr_rdpmc(struct dev
 	if (ret)
 		return ret;
 
+	if (x86_pmu.attr_rdpmc_broken)
+		return -ENOTSUPP;
+
 	if (!!val != !!x86_pmu.attr_rdpmc) {
 		x86_pmu.attr_rdpmc = !!val;
 		smp_call_function(change_rdpmc, (void *)val, 1);
--- a/arch/x86/kernel/cpu/perf_event.h
+++ b/arch/x86/kernel/cpu/perf_event.h
@@ -409,6 +409,7 @@ struct x86_pmu {
 	/*
 	 * sysfs attrs
 	 */
+	int		attr_rdpmc_broken;
 	int		attr_rdpmc;
 	struct attribute **format_attrs;
 	struct attribute **event_attrs;
--- a/arch/x86/kernel/cpu/perf_event_p6.c
+++ b/arch/x86/kernel/cpu/perf_event_p6.c
@@ -231,20 +231,35 @@ static __initconst const struct x86_pmu
 
 };
 
+static __init void p6_pmu_rdpmc_quirk(void)
+{
+	pr_warn("Userspace RDPMC support disabled due to CPU errata\n");
+	x86_pmu.attr_rdpmc_broken = 1;
+	x86_pmu.attr_rdpmc = 0;
+}
+
 __init int p6_pmu_init(void)
 {
 	switch (boot_cpu_data.x86_model) {
-	case 1:
-	case 3:  /* Pentium Pro */
-	case 5:
-	case 6:  /* Pentium II */
-	case 7:
-	case 8:
-	case 11: /* Pentium III */
-	case 9:
-	case 13:
-		/* Pentium M */
+	case  1: /* Pentium Pro */
+		x86_add_quirk(p6_pmu_rdpmc_quirk);
 		break;
+
+	case  3: /* Pentium II - Klamath */
+	case  5: /* Pentium II - Deschutes */
+	case  6: /* Pentium II - Mendocino */
+		break;
+
+	case  7: /* Pentium III - Katmai */
+	case  8: /* Pentium III - Coppermine */
+	case 10: /* Pentium III Xeon */
+	case 11: /* Pentium III - Tualatin */
+		break;
+
+	case  9: /* Pentium M - Banias */
+	case 13: /* Pentium M - Dothan */
+		break;
+
 	default:
 		pr_cont("unsupported p6 CPU model %d ",
 			boot_cpu_data.x86_model);
--
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