From 33c6d6a7ad0ffab9b1b15f8e4107a2af072a05a0 Mon Sep 17 00:00:00 2001 From: Don Zickus Date: Mon, 22 Nov 2010 16:55:23 -0500 Subject: [PATCH] x86, perf, nmi: Disable perf if counters are not accessible In a kvm virt guests, the perf counters are not emulated. Instead they return zero on a rdmsrl. The perf nmi handler uses the fact that crossing a zero means the counter overflowed (for those counters that do not have specific interrupt bits). Therefore on kvm guests, perf will swallow all NMIs thinking the counters overflowed. This causes problems for subsystems like kgdb which needs NMIs to do its magic. This problem was discovered by running kgdb tests. The solution is to write garbage into a perf counter during the initialization and hopefully reading back the same number. On kvm guests, the value will be read back as zero and we disable perf as a result. Reported-by: Jason Wessel Patch-inspired-by: Peter Zijlstra Signed-off-by: Don Zickus Signed-off-by: Peter Zijlstra Cc: Stephane Eranian LKML-Reference: <1290462923-30734-1-git-send-email-dzickus@redhat.com> Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/perf_event.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c index ed6310183ef..6d75b9145b1 100644 --- a/arch/x86/kernel/cpu/perf_event.c +++ b/arch/x86/kernel/cpu/perf_event.c @@ -381,6 +381,20 @@ static void release_pmc_hardware(void) {} #endif +static bool check_hw_exists(void) +{ + u64 val, val_new = 0; + int ret = 0; + + val = 0xabcdUL; + ret |= checking_wrmsrl(x86_pmu.perfctr, val); + ret |= rdmsrl_safe(x86_pmu.perfctr, &val_new); + if (ret || val != val_new) + return false; + + return true; +} + static void reserve_ds_buffers(void); static void release_ds_buffers(void); @@ -1372,6 +1386,12 @@ void __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"); + return; + } + pr_cont("%s PMU driver.\n", x86_pmu.name); if (x86_pmu.quirks) -- 2.41.0