From 4407204c5c9037763aadce39b025529dfbfcac9e Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 8 Dec 2010 15:56:23 +0100 Subject: 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 Cc: Jason Wessel Cc: Don Zickus Cc: Linus Torvalds Cc: Thomas Gleixner Cc: "H. Peter Anvin" LKML-Reference: Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/perf_event.c | 48 +++++++++++++++++++++++++++++++++++----- 1 file 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); -- cgit v1.1