Hello, I could see below within function fdt_add_pmu_nodes() part of hw/arm/virt.c during virt machine initialization time:
Observation: In below function, support of PMU feature is being checked for each vcpu and if the PMU is found part of the features then PMU is initialized with in the host/KVM. But if there is even one vcpu which is found to not support the PMU then loop is exited and PMU is not initialized for the rest of the vcpus as well. static void fdt_add_pmu_nodes(const VirtMachineState *vms) { CPUState *cpu; ARMCPU *armcpu; uint32_t irqflags = GIC_FDT_IRQ_FLAGS_LEVEL_HI; CPU_FOREACH(cpu) { armcpu = ARM_CPU(cpu); if (!arm_feature(&armcpu->env, ARM_FEATURE_PMU)) { return; ------> Here, loop exits & function returns } if (kvm_enabled()) { if (kvm_irqchip_in_kernel()) { kvm_arm_pmu_set_irq(cpu, PPI(VIRTUAL_PMU_IRQ)); } kvm_arm_pmu_init(cpu); } } if (vms->gic_version == VIRT_GIC_VERSION_2) { irqflags = deposit32(irqflags, GIC_FDT_IRQ_PPI_CPU_START, GIC_FDT_IRQ_PPI_CPU_WIDTH, (1 << vms->smp_cpus) - 1); } armcpu = ARM_CPU(qemu_get_cpu(0)); qemu_fdt_add_subnode(vms->fdt, "/pmu"); if (arm_feature(&armcpu->env, ARM_FEATURE_V8)) { const char compat[] = "arm,armv8-pmuv3"; qemu_fdt_setprop(vms->fdt, "/pmu", "compatible", compat, sizeof(compat)); qemu_fdt_setprop_cells(vms->fdt, "/pmu", "interrupts", GIC_FDT_IRQ_TYPE_PPI, VIRTUAL_PMU_IRQ, irqflags); } } Questions: Q1. Not sure what is the logic of the premature exit and not continuing with further checks and initialization of other VCPU PMUs? Q2. Does it even makes sense to have PMUs initialized for some vcpus and not for others unless we have heterogeneous system? Q3. Also, there is a per virt machine knob of vcc->no_pmu. This is something which user could specify at the init time and perhaps only once but we don't use it for ARM. Perhaps should have been used even before entering this function to enable or disable the support as per user config? Q4. This function fdt_* looks to be wrongly named. The info being initialized here shall be used even when ACPI is being used. Initialization part and FDT info looked mixed up here if I am right? Best regards Salil