Ping? About [PATCH v2 2/2], the bad thing is that the customer will not be able to notice the issue, that is, the "Broken BIOS detected" in dmesg, immediately. As a result, the customer VM many panic randomly anytime in the future (once issue is encountered) if "/proc/sys/kernel/unknown_nmi_panic" is enabled. Thank you very much! Dongli Zhang On 12/19/22 06:45, Dongli Zhang wrote: > Can I get feedback for this patchset, especially the [PATCH v2 2/2]? > > About the [PATCH v2 2/2], currently the issue impacts the usage of PMUs on AMD > VM, especially the below case: > > 1. Enable panic on nmi. > 2. Use perf to monitor the performance of VM. Although without a test, I think > the nmi watchdog has the same effect. > 3. A sudden system reset, or a kernel panic (kdump/kexec). > 4. After reboot, there will be random unknown NMI. > 5. Unfortunately, the "panic on nmi" may panic the VM randomly at any time. > > Thank you very much! > > Dongli Zhang > > On 12/1/22 16:22, Dongli Zhang wrote: >> This patchset is to fix two svm pmu virtualization bugs, x86 only. >> >> version 1: >> https://lore.kernel.org/all/20221119122901.2469-1-dongli.zhang@xxxxxxxxxx/ >> >> 1. The 1st bug is that "-cpu,-pmu" cannot disable svm pmu virtualization. >> >> To use "-cpu EPYC" or "-cpu host,-pmu" cannot disable the pmu >> virtualization. There is still below at the VM linux side ... >> >> [ 0.510611] Performance Events: Fam17h+ core perfctr, AMD PMU driver. >> >> ... although we expect something like below. >> >> [ 0.596381] Performance Events: PMU not available due to virtualization, using software events only. >> [ 0.600972] NMI watchdog: Perf NMI watchdog permanently disabled >> >> The 1st patch has introduced a new x86 only accel/kvm property >> "pmu-cap-disabled=true" to disable the pmu virtualization via >> KVM_PMU_CAP_DISABLE. >> >> I considered 'KVM_X86_SET_MSR_FILTER' initially before patchset v1. >> Since both KVM_X86_SET_MSR_FILTER and KVM_PMU_CAP_DISABLE are VM ioctl. I >> finally used the latter because it is easier to use. >> >> >> 2. The 2nd bug is that un-reclaimed perf events (after QEMU system_reset) >> at the KVM side may inject random unwanted/unknown NMIs to the VM. >> >> The svm pmu registers are not reset during QEMU system_reset. >> >> (1). The VM resets (e.g., via QEMU system_reset or VM kdump/kexec) while it >> is running "perf top". The pmu registers are not disabled gracefully. >> >> (2). Although the x86_cpu_reset() resets many registers to zero, the >> kvm_put_msrs() does not puts AMD pmu registers to KVM side. As a result, >> some pmu events are still enabled at the KVM side. >> >> (3). The KVM pmc_speculative_in_use() always returns true so that the events >> will not be reclaimed. The kvm_pmc->perf_event is still active. >> >> (4). After the reboot, the VM kernel reports below error: >> >> [ 0.092011] Performance Events: Fam17h+ core perfctr, Broken BIOS detected, complain to your hardware vendor. >> [ 0.092023] [Firmware Bug]: the BIOS has corrupted hw-PMU resources (MSR c0010200 is 530076) >> >> (5). In a worse case, the active kvm_pmc->perf_event is still able to >> inject unknown NMIs randomly to the VM kernel. >> >> [...] Uhhuh. NMI received for unknown reason 30 on CPU 0. >> >> The 2nd patch is to fix the issue by resetting AMD pmu registers as well as >> Intel registers. >> >> >> This patchset does not cover PerfMonV2, until the below patchset is merged >> into the KVM side. >> >> [PATCH v3 0/8] KVM: x86: Add AMD Guest PerfMonV2 PMU support >> https://lore.kernel.org/all/20221111102645.82001-1-likexu@xxxxxxxxxxx/ >> >> >> Dongli Zhang (2): >> target/i386/kvm: introduce 'pmu-cap-disabled' to set KVM_PMU_CAP_DISABLE >> target/i386/kvm: get and put AMD pmu registers >> >> accel/kvm/kvm-all.c | 1 + >> include/sysemu/kvm_int.h | 1 + >> qemu-options.hx | 7 +++ >> target/i386/cpu.h | 5 ++ >> target/i386/kvm/kvm.c | 129 +++++++++++++++++++++++++++++++++++++++++- >> 5 files changed, 141 insertions(+), 2 deletions(-) >> >> Thank you very much! >> >> Dongli Zhang >> >>
