Re: [PATCH v2 3/7] x86: cpuhp: refuse cpu hot-unplug request earlier if not supported

[Laszlo Ersek]

On 08/18/20 14:22, Igor Mammedov wrote:
> CPU hot-unplug with SMM requires firmware participation to prevent
> guest crash (i.e. CPU can be removed only after OS _and_ firmware
> were prepared for the action).
> Previous patches introduced ICH9_LPC_SMI_F_CPU_HOT_UNPLUG_BIT
> feature bit, which is advertised by firmware when it has support
> for CPU hot-unplug. Use it to check if guest is able to handle
> unplug and make device_del fail gracefully if hot-unplug feature
> hasn't been negotiated.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> Tested-by: Laszlo Ersek <lersek@redhat.com>
> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
> ---
> v2:
>  - fix typo in commit message
>  - drop 5.1 version from hint message (Laszlo)
> ---
>  hw/acpi/ich9.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/hw/acpi/ich9.c b/hw/acpi/ich9.c
> index 0acc9a3107..95cb0f935b 100644
> --- a/hw/acpi/ich9.c
> +++ b/hw/acpi/ich9.c
> @@ -460,6 +460,18 @@ void ich9_pm_device_unplug_request_cb(HotplugHandler 
> *hotplug_dev,
>                                        errp);
>      } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU) &&
>                 !lpc->pm.cpu_hotplug_legacy) {
> +        uint64_t negotiated = lpc->smi_negotiated_features;
> +
> +        if (negotiated & BIT_ULL(ICH9_LPC_SMI_F_BROADCAST_BIT) &&
> +            !(negotiated & BIT_ULL(ICH9_LPC_SMI_F_CPU_HOT_UNPLUG_BIT))) {
> +            error_setg(errp, "cpu hot-unplug with SMI wasn't enabled "
> +                             "by firmware");
> +            error_append_hint(errp, "update machine type to a version having 
> "
> +                                    "x-smi-cpu-hotunplug=on and firmware 
> that "
> +                                    "supports CPU hot-unplug with SMM");
> +            return;
> +        }
> +
>          acpi_cpu_unplug_request_cb(hotplug_dev, &lpc->pm.cpuhp_state,
>                                     dev, errp);
>      } else {
> 

A trivial comment:

Patch#2 says "x86: cphp: " in the subject line, but patch#3 says "x86:
cpuhp: " (note the extra "u").

I'm fine with either "cphp" or "cpuhp", but the subjects should be
consistent -- both patches should use the same word.

Preserve my T-b and R-b on both patches #2 and #3, after fixing up one
of the subjects. (Up to you which one.)

Thanks!
Laszlo