ARM arch does not allow CPUs presence to be changed [1] after kernel has booted. Hence, firmware/ACPI/Qemu must ensure persistent view of the vCPUs to the Guest kernel even when they are not present in the QoM i.e. are unplugged or are yet-to-be-plugged
References: [1] Check comment 5 in the bugzilla entry Link: https://bugzilla.tianocore.org/show_bug.cgi?id=4481#c5 Signed-off-by: Salil Mehta <salil.me...@huawei.com> --- cpu-common.c | 6 ++++++ hw/arm/virt.c | 7 +++++++ include/hw/core/cpu.h | 21 +++++++++++++++++++++ 3 files changed, 34 insertions(+) diff --git a/cpu-common.c b/cpu-common.c index 49d2a50835..e4b4dee99a 100644 --- a/cpu-common.c +++ b/cpu-common.c @@ -128,6 +128,12 @@ bool qemu_enabled_cpu(CPUState *cpu) return cpu && !cpu->disabled; } +bool qemu_persistent_cpu(CPUState *cpu) +{ + /* cpu state can be faked to the guest via acpi */ + return cpu && cpu->acpi_persistent; +} + uint64_t qemu_get_cpu_archid(int cpu_index) { MachineState *ms = MACHINE(qdev_get_machine()); diff --git a/hw/arm/virt.c b/hw/arm/virt.c index 5f98162587..9d33f30a6a 100644 --- a/hw/arm/virt.c +++ b/hw/arm/virt.c @@ -3016,6 +3016,13 @@ static void virt_cpu_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev, return; } virt_cpu_set_properties(OBJECT(cs), cpu_slot, errp); + + /* + * To give persistent presence view of vCPUs to the guest, ACPI might need + * to fake the presence of the vCPUs to the guest but keep them disabled. + * This shall be used during the init of ACPI Hotplug state and hot-unplug + */ + cs->acpi_persistent = true; } static void virt_cpu_plug(HotplugHandler *hotplug_dev, DeviceState *dev, diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h index 62e68611c0..e13e542177 100644 --- a/include/hw/core/cpu.h +++ b/include/hw/core/cpu.h @@ -540,6 +540,14 @@ struct CPUState { * every CPUState is enabled across all architectures. */ bool disabled; + /* + * On certain architectures, to provide a persistent view of the 'presence' + * of vCPUs to the guest, ACPI might need to fake the 'presence' of the + * vCPUs but keep them ACPI-disabled for the guest. This is achieved by + * returning `_STA.PRES=True` and `_STA.Ena=False` for the unplugged vCPUs + * in QEMU QoM. + */ + bool acpi_persistent; /* TODO Move common fields from CPUArchState here. */ int cpu_index; @@ -959,6 +967,19 @@ bool qemu_present_cpu(CPUState *cpu); */ bool qemu_enabled_cpu(CPUState *cpu); +/** + * qemu_persistent_cpu: + * @cpu: The vCPU to check + * + * Checks if the vCPU state should always be reflected as *present* via ACPI + * to the Guest. By default, this is False on all architectures and has to be + * explicity set during initialization. + * + * Returns: True if it is ACPI 'persistent' CPU + * + */ +bool qemu_persistent_cpu(CPUState *cpu); + /** * qemu_get_cpu_archid: * @cpu_index: possible vCPU for which arch-id needs to be retreived -- 2.34.1
