> -----Original Message----- > From: Peter Zijlstra [mailto:peterz@xxxxxxxxxxxxx] > Sent: Tuesday, July 08, 2014 5:29 AM > To: Liang, Kan > Cc: andi@xxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx > Subject: Re: [PATCH V3 1/2] perf ignore LBR and offcore_rsp. > > On Mon, Jul 07, 2014 at 06:34:25AM -0700, kan.liang@xxxxxxxxx wrote: > > @@ -555,7 +577,11 @@ static inline void __x86_pmu_enable_event(struct > > hw_perf_event *hwc, { > > u64 disable_mask = > > __this_cpu_read(cpu_hw_events.perf_ctr_virt_mask); > > > > - if (hwc->extra_reg.reg) > > + if (hwc->extra_reg.reg && > > + ((hwc->extra_reg.idx == EXTRA_REG_RSP_0) ? > > + x86_pmu.extra_msr_access[0] : true) && > > + ((hwc->extra_reg.idx == EXTRA_REG_RSP_1) ? > > + x86_pmu.extra_msr_access[1] : true)) > > wrmsrl(hwc->extra_reg.reg, hwc->extra_reg.config); > > wrmsrl(hwc->config_base, (hwc->config | enable_mask) & > > ~disable_mask); } > > > diff --git a/arch/x86/kernel/cpu/perf_event_intel.c > > b/arch/x86/kernel/cpu/perf_event_intel.c > > index adb02aa..3d18765 100644 > > --- a/arch/x86/kernel/cpu/perf_event_intel.c > > +++ b/arch/x86/kernel/cpu/perf_event_intel.c > > > + /* > > + * Access extra MSR may cause #GP under certain circumstances. > > + * E.g. KVM doesn't support offcore event > > + * Check all extra_regs here. > > + */ > > + if (x86_pmu.extra_regs) { > > + x86_pmu.extra_msr_access[0] = > > + > check_msr(x86_pmu.extra_regs[EXTRA_REG_RSP_0].msr); > > + > > + /* Not all platforms have EXTRA_REG_RSP_1 */ > > + if (x86_pmu.extra_regs[EXTRA_REG_RSP_1].idx == > EXTRA_REG_RSP_1) > > + x86_pmu.extra_msr_access[1] = > > + > check_msr(x86_pmu.extra_regs[EXTRA_REG_RSP_1].msr); > > + /* > > + * If there is no EXTRA_REG_RSP_1 support, > > + * just set the flag to be true. > > + * So it is ignored at the runtime check. > > + */ > > + else > > + x86_pmu.extra_msr_access[1] = true; > > + } > > This too is wrong in many ways; there's more than 2 extra_msrs on many > systems. > Right, there are four extra reg types on Intel systems. Since my previous test only triggers the crash with RSP_0 and RSP_1, so I only handle these two msrs. I will handle all the extra msrs then. > And the place you check is abysmal, if we know at init time that we don't > have those MSRs, WTF do you allow event creation that would use them, > only to then misbehave? Right, we can check it at all the possible creation places. I think the most common place to check should be x86_pmu_extra_regs. For RSP_0 and RSP_1, I also plan to do the check in intel_fixup_er, so extra_reg will not be updated. For LBR select, lbr_sel_map will be cleared at runtime once check_msr failed. Besides the three places, is there any place I missed? Thanks, Kan -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
