Re: [PATCH V1 3/4] hw/acpi: Reflect ACPI vCPU {present,enabled} states in ACPI _STA.{PRES,ENA} Bits

[Gustavo Romero <gustavo.romero@linaro.org>]

Hi Salil,

On 10/14/24 16:22, Salil Mehta wrote:
> Reflect the ACPI CPU hotplug `is_{present, enabled}` states in the `_STA.PRES`
> (presence) and `_STA.ENA` (enabled) bits when the guest kernel evaluates the
> ACPI `_STA` method during initialization, as well as when vCPUs are hot-plugged
> or hot-unplugged. The presence of unplugged vCPUs may need to be deliberately
> *simulated* at the ACPI level to maintain a *persistent* view of vCPUs for the
> guest kernel.
> 
> Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> ---
>   hw/acpi/cpu.c | 26 ++++++++++++++++++++++----
>   1 file changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c
> index 700aa855e9..23ea2b9c70 100644
> --- a/hw/acpi/cpu.c
> +++ b/hw/acpi/cpu.c
> @@ -63,10 +63,11 @@ static uint64_t cpu_hotplug_rd(void *opaque, hwaddr addr, unsigned size)
>       cdev = &cpu_st->devs[cpu_st->selector];
>       switch (addr) {
>       case ACPI_CPU_FLAGS_OFFSET_RW: /* pack and return is_* fields */
> -        val |= cdev->cpu ? 1 : 0;
> +        val |= cdev->is_enabled ? 1 : 0;
>           val |= cdev->is_inserting ? 2 : 0;
>           val |= cdev->is_removing  ? 4 : 0;
>           val |= cdev->fw_remove  ? 16 : 0;
> +        val |= cdev->is_present ? 32 : 0;
>           trace_cpuhp_acpi_read_flags(cpu_st->selector, val);
>           break;
>       case ACPI_CPU_CMD_DATA_OFFSET_RW:
> @@ -376,6 +377,7 @@ const VMStateDescription vmstate_cpu_hotplug = {
>   #define CPU_REMOVE_EVENT  "CRMV"
>   #define CPU_EJECT_EVENT   "CEJ0"
>   #define CPU_FW_EJECT_EVENT "CEJF"
> +#define CPU_PRESENT       "CPRS"
>   
>   void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
>                       build_madt_cpu_fn build_madt_cpu, hwaddr base_addr,
> @@ -436,7 +438,9 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
>           aml_append(field, aml_named_field(CPU_EJECT_EVENT, 1));
>           /* tell firmware to do device eject, write only */
>           aml_append(field, aml_named_field(CPU_FW_EJECT_EVENT, 1));
> -        aml_append(field, aml_reserved_field(3));
> +        /* 1 if present, read only */
> +        aml_append(field, aml_named_field(CPU_PRESENT, 1));
> +        aml_append(field, aml_reserved_field(2));
>           aml_append(field, aml_named_field(CPU_COMMAND, 8));
>           aml_append(cpu_ctrl_dev, field);
>   
> @@ -466,6 +470,7 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
>           Aml *ctrl_lock = aml_name("%s.%s", cphp_res_path, CPU_LOCK);
>           Aml *cpu_selector = aml_name("%s.%s", cphp_res_path, CPU_SELECTOR);
>           Aml *is_enabled = aml_name("%s.%s", cphp_res_path, CPU_ENABLED);
> +        Aml *is_present = aml_name("%s.%s", cphp_res_path, CPU_PRESENT);
>           Aml *cpu_cmd = aml_name("%s.%s", cphp_res_path, CPU_COMMAND);
>           Aml *cpu_data = aml_name("%s.%s", cphp_res_path, CPU_DATA);
>           Aml *ins_evt = aml_name("%s.%s", cphp_res_path, CPU_INSERT_EVENT);
> @@ -494,13 +499,26 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
>           {
>               Aml *idx = aml_arg(0);
>               Aml *sta = aml_local(0);
> +            Aml *ifctx2;
> +            Aml *else_ctx;
>   
>               aml_append(method, aml_acquire(ctrl_lock, 0xFFFF));
>               aml_append(method, aml_store(idx, cpu_selector));
>               aml_append(method, aml_store(zero, sta));
> -            ifctx = aml_if(aml_equal(is_enabled, one));
> +            ifctx = aml_if(aml_equal(is_present, one));
>               {
> -                aml_append(ifctx, aml_store(aml_int(0xF), sta));
> +                ifctx2 = aml_if(aml_equal(is_enabled, one));
> +                {
> +                    /* cpu is present and enabled */
> +                    aml_append(ifctx2, aml_store(aml_int(0xF), sta));
> +                }
> +                aml_append(ifctx, ifctx2);
> +                else_ctx = aml_else();
> +                {
> +                    /* cpu is present but disabled */
> +                    aml_append(else_ctx, aml_store(aml_int(0xD), sta));

Here, the return value for _STA method is set to reflect the state of
CPU_PRESENT and CPU_ENABLED fields. I can't see these two fields being
mapped to AcpiCpuStatus.{is_present,is_enabled}. They look to be mapped
to the MMIO region (base_addr), which doesn't mapped to AcpiCpuStatus
afaics. So where CPU_PRESENT and CPU_ENABLED are set and where exactly
they reside?


Cheers,
Gustavo

> +                }
> +                aml_append(ifctx, else_ctx);
>               }
>               aml_append(method, ifctx);
>               aml_append(method, aml_release(ctrl_lock));