pmu: fixes for Sandy Bridge hosts

Commit Message

Paolo Bonzini May 30, 2013, 5:43 p.m. UTC

This patch includes two fixes for SB:

* the 3rd fixed counter ("ref cpu cycles") can sometimes report
  less than the number of iterations

* there is an 8th counter which causes out of bounds accesses
  to gp_event or check_counters_many's cnt array

There is still a bug in KVM, because the "pmu all counters-0"
test fails.  (It passes if you use any 6 of the 8 gp counters,
fails if you use 7 or 8).
---
 x86/pmu.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

Comments

Paolo Bonzini May 30, 2013, 5:45 p.m. UTC | #1

Il 30/05/2013 19:43, Paolo Bonzini ha scritto:
> @@ -395,6 +396,14 @@ int main(int ac, char **av)
>  	printf("Fixed counters:      %d\n", edx.split.num_counters_fixed);
>  	printf("Fixed counter width: %d\n", edx.split.bit_width_fixed);
>  
> +	num_counters = eax.split.num_counters;
> +	if (num_counters > ARRAY_SIZE(gp_events))
> +		num_counters = ARRAY_SIZE(gp_events);
> +	while (id.b) {
> +		num_counters--;
> +		id.b &= id.b - 1;
> +	}
> +
>  	apic_write(APIC_LVTPC, PC_VECTOR);
>  
>  	check_gp_counters();
> 

Please ignore this patch.  The parent one with "[PATCH kvm-unit-tests]"
subject is good though.

Paolo
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Patch

diff --git a/x86/pmu.c b/x86/pmu.c
index 2c46f31..dca753a 100644
--- a/x86/pmu.c
+++ b/x86/pmu.c
@@ -88,9 +88,10 @@  struct pmu_event {
 }, fixed_events[] = {
 	{"fixed 1", MSR_CORE_PERF_FIXED_CTR0, 10*N, 10.2*N},
 	{"fixed 2", MSR_CORE_PERF_FIXED_CTR0 + 1, 1*N, 30*N},
-	{"fixed 3", MSR_CORE_PERF_FIXED_CTR0 + 2, 1*N, 30*N}
+	{"fixed 3", MSR_CORE_PERF_FIXED_CTR0 + 2, 0.1*N, 30*N}
 };
 
+static int num_counters;
 static int tests, failures;
 
 char *buf;
@@ -237,7 +238,7 @@  static void check_gp_counter(struct pmu_event *evt)
 	};
 	int i;
 
-	for (i = 0; i < eax.split.num_counters; i++, cnt.ctr++) {
+	for (i = 0; i < num_counters; i++, cnt.ctr++) {
 		cnt.count = 0;
 		measure(&cnt, 1);
 		report(evt->name, i, verify_event(cnt.count, evt));
@@ -276,7 +277,7 @@  static void check_counters_many(void)
 	pmu_counter_t cnt[10];
 	int i, n;
 
-	for (i = 0, n = 0; n < eax.split.num_counters; i++) {
+	for (i = 0, n = 0; n < num_counters; i++) {
 		if (ebx.full & (1 << i))
 			continue;
 
@@ -316,10 +317,10 @@  static void check_counter_overflow(void)
 	/* clear status before test */
 	wrmsr(MSR_CORE_PERF_GLOBAL_OVF_CTRL, rdmsr(MSR_CORE_PERF_GLOBAL_STATUS));
 
-	for (i = 0; i < eax.split.num_counters + 1; i++, cnt.ctr++) {
+	for (i = 0; i < num_counters + 1; i++, cnt.ctr++) {
 		uint64_t status;
 		int idx;
-		if (i == eax.split.num_counters)
+		if (i == num_counters)
 			cnt.ctr = fixed_events[0].unit_sel;
 		if (i % 2)
 			cnt.config |= EVNTSEL_INT;
@@ -355,7 +356,7 @@  static void check_rdpmc(void)
 	uint64_t val = 0x1f3456789ull;
 	int i;
 
-	for (i = 0; i < eax.split.num_counters; i++) {
+	for (i = 0; i < num_counters; i++) {
 		uint64_t x = (val & 0xffffffff) |
 			((1ull << (eax.split.bit_width - 32)) - 1) << 32;
 		wrmsr(MSR_IA32_PERFCTR0 + i, val);
@@ -395,6 +396,14 @@  int main(int ac, char **av)
 	printf("Fixed counters:      %d\n", edx.split.num_counters_fixed);
 	printf("Fixed counter width: %d\n", edx.split.bit_width_fixed);
 
+	num_counters = eax.split.num_counters;
+	if (num_counters > ARRAY_SIZE(gp_events))
+		num_counters = ARRAY_SIZE(gp_events);
+	while (id.b) {
+		num_counters--;
+		id.b &= id.b - 1;
+	}
+
 	apic_write(APIC_LVTPC, PC_VECTOR);
 
 	check_gp_counters();