On Wed, 13 Sep 2023 16:38:20 +0000
James Morse <james.morse@xxxxxxx> wrote:
> acpi_processor_get_info() registers all present CPUs. Registering a
> CPU is what creates the sysfs entries and triggers the udev
> notifications.
>
> arm64 virtual machines that support 'virtual cpu hotplug' use the
> enabled bit to indicate whether the CPU can be brought online, as
> the existing ACPI tables require all hardware to be described and
> present.
>
> If firmware describes a CPU as present, but disabled, skip the
> registration. Such CPUs are present, but can't be brought online for
> whatever reason. (e.g. firmware/hypervisor policy).
>
> Once firmware sets the enabled bit, the CPU can be registered and
> brought online by user-space. Online CPUs, or CPUs that are missing
> an _STA method must always be registered.
>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
A small argument with myself inline. Feel free to ignore.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> ---
> drivers/acpi/acpi_processor.c | 31 ++++++++++++++++++++++++++++++-
> 1 file changed, 30 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index b67616079751..b49859eab01a 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -227,6 +227,32 @@ static int acpi_processor_make_present(struct acpi_processor *pr)
> return ret;
> }
>
> +static int acpi_processor_make_enabled(struct acpi_processor *pr)
> +{
> + unsigned long long sta;
> + acpi_status status;
> + bool present, enabled;
> +
> + if (!acpi_has_method(pr->handle, "_STA"))
> + return arch_register_cpu(pr->id);
> +
> + status = acpi_evaluate_integer(pr->handle, "_STA", NULL, &sta);
> + if (ACPI_FAILURE(status))
> + return -ENODEV;
> +
> + present = sta & ACPI_STA_DEVICE_PRESENT;
> + enabled = sta & ACPI_STA_DEVICE_ENABLED;
> +
> + if (cpu_online(pr->id) && (!present || !enabled)) {
> + pr_err_once(FW_BUG "CPU %u is online, but described as not present or disabled!\n", pr->id);
Why once? If this for some reason happened on multiple CPUs I think we'd want to know.
> + add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_STILL_OK);
> + } else if (!present || !enabled) {
> + return -ENODEV;
> + }
I guess you didn't do a nested if here to avoid even longer lines.
Could flip things around though I don't like this much either as it makes
the normal good path exit mid way down.
if (present && enabled)
return arch_register_cpu(pr->id);
if (!cpu_online(pr->id))
return -ENODEV;
pr_err...
add_taint(...
return arch_register_cpu(pr->id);
Ah well. Some code just has to be less than pretty.
> +
> + return arch_register_cpu(pr->id);
> +}
> +
> static int acpi_processor_get_info(struct acpi_device *device)
> {
> union acpi_object object = { 0 };
> @@ -318,7 +344,7 @@ static int acpi_processor_get_info(struct acpi_device *device)
> */
> if (!invalid_logical_cpuid(pr->id) && cpu_present(pr->id) &&
> !get_cpu_device(pr->id)) {
> - int ret = arch_register_cpu(pr->id);
> + int ret = acpi_processor_make_enabled(pr);
>
> if (ret)
> return ret;
> @@ -526,6 +552,9 @@ static void acpi_processor_post_eject(struct acpi_device *device)
> acpi_processor_make_not_present(device);
> return;
> }
> +
> + if (cpu_present(pr->id) && !(sta & ACPI_STA_DEVICE_ENABLED))
> + arch_unregister_cpu(pr->id);
> }
>
> #ifdef CONFIG_ARCH_MIGHT_HAVE_ACPI_PDC
