Messages in this thread Patch in this message | | | Subject | Re: perf hw in kexeced kernel broken in tip | From | Peter Zijlstra <> | Date | Wed, 08 Dec 2010 15:59:16 +0100 |
| |
On Wed, 2010-12-08 at 15:20 +0100, Peter Zijlstra wrote:
> > I wonder if you should reverse these checks. If the bios has the perf > > counter enabled, there might be a high chance that it fails the first > > check and never gets to the actually bios checks. > > Ah, good point.
Something like so..
--- Subject: perf, x86: Detect broken BIOSes From: Peter Zijlstra <a.p.zijlstra@chello.nl> Date: Wed Dec 08 15:56:23 CET 2010
Some BIOSes use PMU resources, this is a bug.
Try to detect this, warn about it, and further refuse to touch the PMU ourselves.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> --- Index: linux-2.6/arch/x86/kernel/cpu/perf_event.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/cpu/perf_event.c +++ linux-2.6/arch/x86/kernel/cpu/perf_event.c @@ -375,15 +375,51 @@ 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; + } + + for (i = 0; i < x86_pmu.num_counters_fixed; i++) { + reg = MSR_ARCH_PERFMON_FIXED_CTR_CTRL; + ret = rdmsrl_safe(reg, &val); + if (ret) + goto msr_fail; + 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, software events only.\n"); + printk(KERN_ERR FW_BUG "invalid MSR: %x=%Lx\n", reg, val); + return false; + +msr_fail: + printk(KERN_CONT "Broken PMU hardware detected, software events only.\n"); + return false; } static void reserve_ds_buffers(void); @@ -1378,10 +1414,8 @@ 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);
| |