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 > >
