Re: [RFC PATCH 3/5] hw/arm/virt-acpi-build: distinguish possible and present cpus

[Andrew Jones <drjones@redhat.com>]

On Thu, Feb 25, 2021 at 04:56:25PM +0800, Ying Fang wrote:
> When building ACPI tables regarding CPUs we should always build
> them for the number of possible CPUs, not the number of present
> CPUs. We then ensure only the present CPUs are enabled in madt.
> Furthermore, it is also needed if we are going to support CPU
> hotplug in the future.
> 
> This patch is a rework based on Andrew Jones's contribution at
> https://lists.gnu.org/archive/html/qemu-arm/2018-07/msg00076.html
> 
> Signed-off-by: Ying Fang <fangying1@huawei.com>
> ---
>  hw/arm/virt-acpi-build.c | 14 ++++++++++----
>  hw/arm/virt.c            |  2 ++
>  2 files changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index f9c9df916c..bb91152fe2 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -61,13 +61,16 @@
>  
>  static void acpi_dsdt_add_cpus(Aml *scope, VirtMachineState *vms)
>  {
> -    MachineState *ms = MACHINE(vms);
> +    CPUArchIdList *possible_cpus = MACHINE(vms)->possible_cpus;
>      uint16_t i;
>  
> -    for (i = 0; i < ms->smp.cpus; i++) {
> +    for (i = 0; i < possible_cpus->len; i++) {

Switching from ms->smp.cpus to possible_cpus->len makes some sense
here, since we're going to be using possible_cpus->cpus[] inside
the loop. Otherwise, I'd prefer switching to ms->smp.max_cpus.

>          Aml *dev = aml_device("C%.03X", i);
>          aml_append(dev, aml_name_decl("_HID", aml_string("ACPI0007")));
>          aml_append(dev, aml_name_decl("_UID", aml_int(i)));
> +        if (possible_cpus->cpus[i].cpu == NULL) {
> +            aml_append(dev, aml_name_decl("_STA", aml_int(0)));
> +        }
>          aml_append(scope, dev);
>      }
>  }
> @@ -479,6 +482,7 @@ build_madt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
>      const int *irqmap = vms->irqmap;
>      AcpiMadtGenericDistributor *gicd;
>      AcpiMadtGenericMsiFrame *gic_msi;
> +    CPUArchIdList *possible_cpus = MACHINE(vms)->possible_cpus;
>      int i;
>  
>      acpi_data_push(table_data, sizeof(AcpiMultipleApicTable));
> @@ -489,7 +493,7 @@ build_madt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
>      gicd->base_address = cpu_to_le64(memmap[VIRT_GIC_DIST].base);
>      gicd->version = vms->gic_version;
>  
> -    for (i = 0; i < MACHINE(vms)->smp.cpus; i++) {
> +    for (i = 0; i < possible_cpus->len; i++) {

Same comment as above.

>          AcpiMadtGenericCpuInterface *gicc = acpi_data_push(table_data,
>                                                             sizeof(*gicc));
>          ARMCPU *armcpu = ARM_CPU(qemu_get_cpu(i));
> @@ -504,7 +508,9 @@ build_madt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
>          gicc->cpu_interface_number = cpu_to_le32(i);
>          gicc->arm_mpidr = cpu_to_le64(armcpu->mp_affinity);
>          gicc->uid = cpu_to_le32(i);
> -        gicc->flags = cpu_to_le32(ACPI_MADT_GICC_ENABLED);
> +        if (possible_cpus->cpus[i].cpu != NULL) {
> +            gicc->flags = cpu_to_le32(ACPI_MADT_GICC_ENABLED);
> +        }
>  
>          if (arm_feature(&armcpu->env, ARM_FEATURE_PMU)) {
>              gicc->performance_interrupt = cpu_to_le32(PPI(VIRTUAL_PMU_IRQ));
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index c133b342b8..75659502e2 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -2047,6 +2047,8 @@ static void machvirt_init(MachineState *machine)
>  
>          qdev_realize(DEVICE(cpuobj), NULL, &error_fatal);
>          object_unref(cpuobj);
> +        /* Initialize cpu member here since cpu hotplug is not supported yet */
> +        machine->possible_cpus->cpus[n].cpu = cpuobj;

This feels like we're violating a possible_cpus abstraction. Igor?
Also, it's using cpuobj after unrefing it.

>      }
>      fdt_add_timer_nodes(vms);
>      fdt_add_cpu_nodes(vms);
> -- 
> 2.23.0
> 
> 

Thanks,
drew