Hi Alex, On Mon, Dec 6, 2021 at 9:02 AM Alexandru Elisei <alexandru.elisei@xxxxxxx> wrote: > > (CC'ing Peter Maydell in case this might be of interest to qemu) > > The series can be found on a branch at [1], and the kvmtool support at [2]. > The kvmtool patches are also on the mailing list [3] and haven't changed > since v1. > > Detailed explanation of the issue and symptoms that the patches attempt to > correct can be found in the cover letter for v1 [4]. > > A brief summary of the problem is that on heterogeneous systems KVM will > always use the same PMU for creating the VCPU events for *all* VCPUs > regardless of the physical CPU on which the VCPU is running, leading to > events suddenly stopping and resuming in the guest as the VCPU thread gets > migrated across different CPUs. > > This series proposes to fix this behaviour by allowing the user to specify > which physical PMU is used when creating the VCPU events needed for guest > PMU emulation. When the PMU is set, KVM will refuse to the VCPU on a > physical which is not part of the supported CPUs for the specified PMU. Just to confirm, this series provides an API for userspace to request KVM to detect a wrong affinity setting due to a userspace bug so that userspace can get an error at KVM_RUN instead of leading to events suddenly stopping, correct ? > The default behaviour stays the same - without userspace setting the PMU, > events will stop counting if the VCPU is scheduled on the wrong CPU. Can't we fix the default behavior (in addition to the current fix) ? (Do we need to maintain the default behavior ??) IMHO I feel it is better to prevent userspace from configuring PMU for guests on such heterogeneous systems rather than leading to events suddenly stopping even as the default behavior. Thanks, Reiji > > Changes since v1: > > - Rebased on top of v5.16-rc4 > > - Implemented review comments: protect iterating through the list of PMUs > with a mutex, documentation changes, initialize vcpu-arch.supported_cpus > to cpu_possible_mask, changed vcpu->arch.cpu_not_supported to a VCPU > flag, set exit reason to KVM_EXIT_FAIL_ENTRY and populate fail_entry when > the VCPU is run on a CPU not in the PMU's supported cpumask. Many thanks > for the review! > > [1] https://gitlab.arm.com/linux-arm/linux-ae/-/tree/pmu-big-little-fix-v2 > [2] https://gitlab.arm.com/linux-arm/kvmtool-ae/-/tree/pmu-big-little-fix-v1 > [3] https://www.spinics.net/lists/arm-kernel/msg933584.html > [4] https://www.spinics.net/lists/arm-kernel/msg933579.html > > Alexandru Elisei (4): > perf: Fix wrong name in comment for struct perf_cpu_context > KVM: arm64: Keep a list of probed PMUs > KVM: arm64: Add KVM_ARM_VCPU_PMU_V3_SET_PMU attribute > KVM: arm64: Refuse to run VCPU if the PMU doesn't match the physical > CPU > > Documentation/virt/kvm/devices/vcpu.rst | 29 +++++++++++ > arch/arm64/include/asm/kvm_host.h | 12 +++++ > arch/arm64/include/uapi/asm/kvm.h | 4 ++ > arch/arm64/kvm/arm.c | 19 ++++++++ > arch/arm64/kvm/pmu-emul.c | 64 +++++++++++++++++++++++-- > include/kvm/arm_pmu.h | 6 +++ > include/linux/perf_event.h | 2 +- > tools/arch/arm64/include/uapi/asm/kvm.h | 1 + > 8 files changed, 132 insertions(+), 5 deletions(-) > > -- > 2.34.1 > > _______________________________________________ > kvmarm mailing list > kvmarm@xxxxxxxxxxxxxxxxxxxxx > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
