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SubjectRE: [PATCH v1 05/11] KVM: x86/pmu: Add support to reprogram PEBS event for guest counters
Date
> -----Original Message-----
> From: kbuild test robot <lkp@intel.com>
> Sent: Saturday, March 7, 2020 12:28 AM
> To: Luwei Kang <luwei.kang@intel.com>
> Cc: kbuild-all@lists.01.org; x86@kernel.org; linux-kernel@vger.kernel.org;
> kvm@vger.kernel.org; peterz@infradead.org; mingo@redhat.com;
> acme@kernel.org; mark.rutland@arm.com;
> alexander.shishkin@linux.intel.com; jolsa@redhat.com;
> namhyung@kernel.org; tglx@linutronix.de; bp@alien8.de; hpa@zytor.com;
> pbonzini@redhat.com; sean.j.christopherson@intel.com;
> vkuznets@redhat.com; wanpengli@tencent.com; jmattson@google.com;
> joro@8bytes.org; pawan.kumar.gupta@linux.intel.com; ak@linux.intel.com;
> thomas.lendacky@amd.com; fenghua.yu@intel.com;
> kan.liang@linux.intel.com; like.xu@linux.intel.com
> Subject: Re: [PATCH v1 05/11] KVM: x86/pmu: Add support to reprogram PEBS
> event for guest counters
>
> Hi Luwei,
>
> Thank you for the patch! Yet something to improve:
>
> [auto build test ERROR on kvm/linux-next] [also build test ERROR on
> tip/perf/core tip/auto-latest v5.6-rc4 next-20200306] [if your patch is applied to
> the wrong git tree, please drop us a note to help improve the system. BTW, we
> also suggest to use '--base' option to specify the base tree in git format-patch,
> please see https://stackoverflow.com/a/37406982]
>
> url:
> https://github.com/0day-ci/linux/commits/Luwei-Kang/PEBS-virtualization-ena
> bling-via-DS/20200306-013049
> base: https://git.kernel.org/pub/scm/virt/kvm/kvm.git linux-next
> config: x86_64-randconfig-h003-20200305 (attached as .config)
> compiler: gcc-7 (Debian 7.5.0-5) 7.5.0
> reproduce:
> # save the attached .config to linux build tree
> make ARCH=x86_64
>
> If you fix the issue, kindly add following tag
> Reported-by: kbuild test robot <lkp@intel.com>
>
> All errors (new ones prefixed by >>):
>
> ld: arch/x86/kvm/pmu.o: in function `pmc_reprogram_counter':
> >> arch/x86/kvm/pmu.c:199: undefined reference to
> `perf_x86_pmu_unset_auto_reload'

Since we may not lose PEBS functionality for other x86 vendors on KVM
and we already have defined PERF_X86_EVENT_AUTO_RELOAD in the general
arch/x86/events/perf_event.h,

one of the ways to fix this issue is to
move the definition of perf_x86_pmu_unset_auto_reload()
to the end of arch/x86/events/core.c
instead of making it Intel specific
in previous patch "perf/x86: Expose a function to disable auto-reload."

Thanks,
Like Xu

>
> vim +199 arch/x86/kvm/pmu.c
>
> 101
> 102 static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
> 103 unsigned config, bool exclude_user,
> 104 bool exclude_kernel, bool intr,
> 105 bool in_tx, bool in_tx_cp)
> 106 {
> 107 struct kvm_pmu *pmu = vcpu_to_pmu(pmc->vcpu);
> 108 struct perf_event *event;
> 109 struct perf_event_attr attr = {
> 110 .type = type,
> 111 .size = sizeof(attr),
> 112 .pinned = true,
> 113 .exclude_idle = true,
> 114 .exclude_host = 1,
> 115 .exclude_user = exclude_user,
> 116 .exclude_kernel = exclude_kernel,
> 117 .config = config,
> 118 .disabled = 1,
> 119 };
> 120 bool pebs = test_bit(pmc->idx, (unsigned long
> *)&pmu->pebs_enable);
> 121
> 122 attr.sample_period = (-pmc->counter) & pmc_bitmask(pmc);
> 123
> 124 if (in_tx)
> 125 attr.config |= HSW_IN_TX;
> 126 if (in_tx_cp) {
> 127 /*
> 128 * HSW_IN_TX_CHECKPOINTED is not supported with
> nonzero
> 129 * period. Just clear the sample period so at least
> 130 * allocating the counter doesn't fail.
> 131 */
> 132 attr.sample_period = 0;
> 133 attr.config |= HSW_IN_TX_CHECKPOINTED;
> 134 }
> 135
> 136 if (pebs) {
> 137 /*
> 138 * Host never knows the precision level set by guest.
> 139 * Force Host's PEBS event to precision level 1, which will
> 140 * not impact the accuracy of the results for guest PEBS
> events.
> 141 * Because,
> 142 * - For most cases, there is no difference among precision
> 143 * level 1 to 3 for PEBS events.
> 144 * - The functions as below checks the precision level in
> host.
> 145 * But the results from these functions in host are
> replaced
> 146 * by guest when sampling the guest.
> 147 * The accuracy for guest PEBS events will not be
> impacted.
> 148 * -- event_constraints() impacts the index of counter.
> 149 * The index for host event is exactly the same as guest.
> 150 * It's decided by guest.
> 151 * -- pebs_update_adaptive_cfg() impacts the value of
> 152 * MSR_PEBS_DATA_CFG. When guest is switched in,
> 153 * the MSR value will be replaced by the value from
> guest.
> 154 * -- setup_sample () impacts the output of a PEBS
> record.
> 155 * Guest handles the PEBS records.
> 156 */
> 157 attr.precise_ip = 1;
> 158 /*
> 159 * When the host's PMI handler completes, it's going to
> 160 * enter the guest and trigger the guest's PMI handler.
> 161 *
> 162 * At this moment, this function may be called by
> 163 * kvm_pmu_handle_event(). However the next
> sample_period
> 164 * hasn't been determined by guest yet and the left period,
> 165 * which probably be 0, is used for current sample_period.
> 166 *
> 167 * In this case, perf will mistakenly treat it as non
> 168 * sampling events. The PEBS event will error out.
> 169 *
> 170 * Fill it with maximum period to prevent the error out.
> 171 * The guest PMI handler will soon reprogram the counter.
> 172 */
> 173 if (!attr.sample_period)
> 174 attr.sample_period = (-1ULL) & pmc_bitmask(pmc);
> 175 }
> 176
> 177 event = perf_event_create_kernel_counter(&attr, -1, current,
> 178 (intr || pebs) ?
> 179 kvm_perf_overflow_intr :
> 180 kvm_perf_overflow, pmc);
> 181 if (IS_ERR(event)) {
> 182 pr_debug_ratelimited("kvm_pmu: event creation failed %ld
> for pmc->idx = %d\n",
> 183 PTR_ERR(event), pmc->idx);
> 184 return;
> 185 }
> 186
> 187 if (pebs) {
> 188 event->guest_dedicated_idx = pmc->idx;
> 189 /*
> 190 * For guest PEBS events, guest takes the responsibility to
> 191 * drain PEBS buffers, and load proper values to reset
> counters.
> 192 *
> 193 * Host will unconditionally set auto-reload flag for PEBS
> 194 * events with fixed period which is not necessary. Host
> should
> 195 * do nothing in drain_pebs() but inject the PMI into the
> guest.
> 196 *
> 197 * Unset the auto-reload flag for guest PEBS events.
> 198 */
> > 199 perf_x86_pmu_unset_auto_reload(event);
> 200 }
> 201 pmc->perf_event = event;
> 202 pmc_to_pmu(pmc)->event_count++;
> 203 perf_event_enable(event);
> 204 clear_bit(pmc->idx, pmc_to_pmu(pmc)->reprogram_pmi);
> 205 }
> 206
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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