[PATCH v2] perf/x86: descriptive failure messages for PMU init

[Bandan Das <bsd@redhat.com>]

There's a default warning message that gets printed, however,
there are various failure conditions:
 - a msr read can fail
 - a msr write can fail
 - a msr has an unexpected value
 - all msrs have unexpected values (disable PMU)

Lastly, use %llx to silence checkpatch

Signed-off-by: Bandan Das <bsd@redhat.com>
---
v2:
 Remove virt specific pr_debugs
 Change the default warning message

 arch/x86/events/core.c | 53 +++++++++++++++++++++++++++++++-----------
 1 file changed, 40 insertions(+), 13 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 81911e11a15d..52b0893da78b 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -192,9 +192,16 @@ static void release_pmc_hardware(void) {}
 
 static bool check_hw_exists(void)
 {
-	u64 val, val_fail = -1, val_new= ~0;
-	int i, reg, reg_fail = -1, ret = 0;
-	int bios_fail = 0;
+	u64 val = -1, val_fail = -1, val_new = ~0;
+	int i, reg = -1, reg_fail = -1, ret = 0;
+
+	enum {
+	      READ_FAIL	   =	1,
+	      WRITE_FAIL   =	2,
+	      PMU_FAIL	   =	3,
+	      BIOS_FAIL	   =	4,
+	};
+	int status = 0;
 	int reg_safe = -1;
 
 	/*
@@ -204,10 +211,13 @@ static bool check_hw_exists(void)
 	for (i = 0; i < x86_pmu.num_counters; i++) {
 		reg = x86_pmu_config_addr(i);
 		ret = rdmsrl_safe(reg, &val);
-		if (ret)
+		if (ret) {
+			status = READ_FAIL;
 			goto msr_fail;
+		}
+
 		if (val & ARCH_PERFMON_EVENTSEL_ENABLE) {
-			bios_fail = 1;
+			status = BIOS_FAIL;
 			val_fail = val;
 			reg_fail = reg;
 		} else {
@@ -218,11 +228,13 @@ static bool check_hw_exists(void)
 	if (x86_pmu.num_counters_fixed) {
 		reg = MSR_ARCH_PERFMON_FIXED_CTR_CTRL;
 		ret = rdmsrl_safe(reg, &val);
-		if (ret)
+		if (ret) {
+			status = READ_FAIL;
 			goto msr_fail;
+		}
 		for (i = 0; i < x86_pmu.num_counters_fixed; i++) {
 			if (val & (0x03 << i*4)) {
-				bios_fail = 1;
+				status = BIOS_FAIL;
 				val_fail = val;
 				reg_fail = reg;
 			}
@@ -236,7 +248,7 @@ static bool check_hw_exists(void)
 	 */
 
 	if (reg_safe == -1) {
-		reg = reg_safe;
+		status = PMU_FAIL;
 		goto msr_fail;
 	}
 
@@ -246,18 +258,22 @@ static bool check_hw_exists(void)
 	 * (qemu/kvm) that don't trap on the MSR access and always return 0s.
 	 */
 	reg = x86_pmu_event_addr(reg_safe);
-	if (rdmsrl_safe(reg, &val))
+	if (rdmsrl_safe(reg, &val)) {
+		status = READ_FAIL;
 		goto msr_fail;
+	}
 	val ^= 0xffffUL;
 	ret = wrmsrl_safe(reg, val);
 	ret |= rdmsrl_safe(reg, &val_new);
-	if (ret || val != val_new)
+	if (ret || val != val_new) {
+		status = WRITE_FAIL;
 		goto msr_fail;
+	}
 
 	/*
 	 * We still allow the PMU driver to operate:
 	 */
-	if (bios_fail) {
+	if (status == BIOS_FAIL) {
 		pr_cont("Broken BIOS detected, complain to your hardware vendor.\n");
 		pr_err(FW_BUG "the BIOS has corrupted hw-PMU resources (MSR %x is %Lx)\n",
 			      reg_fail, val_fail);
@@ -270,8 +286,19 @@ static bool check_hw_exists(void)
 		pr_cont("PMU not available due to virtualization, using software events only.\n");
 	} else {
 		pr_cont("Broken PMU hardware detected, using software events only.\n");
-		pr_err("Failed to access perfctr msr (MSR %x is %Lx)\n",
-		       reg, val_new);
+	}
+	switch (status) {
+	case READ_FAIL:
+		pr_err("Failed to read perfctr msr (MSR %x)\n", reg);
+		break;
+	case WRITE_FAIL:
+		pr_err("Failed to write perfctr msr (MSR %x, wrote: %llx, read: %llx)\n",
+		       reg, val, val_new);
+		break;
+	case PMU_FAIL:
+		/* fall through for default message */
+	default:
+		pr_err(FW_BUG "the BIOS has corrupted hw-PMU resources.\n");
 	}
 
 	return false;
-- 
2.19.2