[tip:perf/core] perf, x86: Detect broken BIOSes that corrupt the PMU

tip-bot for Peter Zijlstra
2010-12-16T12:32:55Z

Commit-ID: 4407204c5c9037763aadce39b025529dfbfcac9e
Gitweb: http://git.kernel.org/tip/4407204c5c9037763aadce39b025529dfbfcac9e
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Wed, 8 Dec 2010 15:56:23 +0100
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 16 Dec 2010 11:36:42 +0100

perf, x86: Detect broken BIOSes that corrupt the PMU

Some BIOSes use PMU resources, which can cause various bugs:

- Non-working or erratic PMU based statistics - the PMU can end up
counting the wrong thing, resulting in misleading statistics

- Profiling can stop working or it can profile the wrong thing

- A non-working or erratic NMI watchdog that cannot be relied on

- The kernel may disturb whatever thing the BIOS tries to use the
PMU for - possibly causing hardware malfunction in extreme cases.

- ... and other forms of potential misbehavior

Various forms of such misbehavior has been observed in practice - there are
BIOSes that just corrupt the PMU state, consequences be damned.

The PMU is a CPU resource that is handled by the kernel and the BIOS
stealing+corrupting it is not acceptable nor robust, so we detect it,
warn about it and further refuse to touch the PMU ourselves.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
arch/x86/kernel/cpu/perf_event.c | 48 +++++++++++++++++++++++++++++++++----
1 files changed, 42 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 817d2b1..ce27c54 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -375,15 +375,53 @@ static void release_pmc_hardware(void) {}
static bool check_hw_exists(void)
{
u64 val, val_new = 0;
- int ret = 0;
+ int i, reg, ret = 0;
+
+ /*
+ * Check to see if the BIOS enabled any of the counters, if so
+ * complain and bail.
+ */
+ for (i = 0; i < x86_pmu.num_counters; i++) {
+ reg = x86_pmu.eventsel + i;
+ ret = rdmsrl_safe(reg, &val);
+ if (ret)
+ goto msr_fail;
+ if (val & ARCH_PERFMON_EVENTSEL_ENABLE)
+ goto bios_fail;
+ }
+
+ if (x86_pmu.num_counters_fixed) {
+ reg = MSR_ARCH_PERFMON_FIXED_CTR_CTRL;
+ ret = rdmsrl_safe(reg, &val);
+ if (ret)
+ goto msr_fail;
+ for (i = 0; i < x86_pmu.num_counters_fixed; i++) {
+ if (val & (0x03 << i*4))
+ goto bios_fail;
+ }
+ }

+ /*
+ * Now write a value and read it back to see if it matches,
+ * this is needed to detect certain hardware emulators (qemu/kvm)
+ * that don't trap on the MSR access and always return 0s.
+ */
val = 0xabcdUL;
- ret |= checking_wrmsrl(x86_pmu.perfctr, val);
+ ret = checking_wrmsrl(x86_pmu.perfctr, val);
ret |= rdmsrl_safe(x86_pmu.perfctr, &val_new);
if (ret || val != val_new)
- return false;
+ goto msr_fail;

return true;
+
+bios_fail:
+ printk(KERN_CONT "Broken BIOS detected, using software events only.\n");
+ printk(KERN_ERR FW_BUG "the BIOS has corrupted hw-PMU resources (MSR %x is %Lx)\n", reg, val);
+ return false;
+
+msr_fail:
+ printk(KERN_CONT "Broken PMU hardware detected, using software events only.\n");
+ return false;
}

static void reserve_ds_buffers(void);
@@ -1378,10 +1416,8 @@ int __init init_hw_perf_events(void)
pmu_check_apic();

/* sanity check that the hardware exists or is emulated */
- if (!check_hw_exists()) {
- pr_cont("Broken PMU hardware detected, software events only.\n");
+ if (!check_hw_exists())
return 0;
- }

pr_cont("%s PMU driver.\n", x86_pmu.name);