On 10/5/2023 6:13 AM, Kirill A. Shutemov wrote:
> ACPI MADT doesn't allow to offline CPU after it got woke up.
>
I think you can use the term "CPU hotplug" instead of just offline.
> Currently hotplug prevented based on the confidential computing
> attribute which is set for Intel TDX. But TDX is not the only possible
> user of the wake up method.
>
> Mark CPU hotplug as "not supported" on ACPI MADT wakeup enumeration.
Looks good to me.
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
> arch/x86/coco/core.c | 1 -
> arch/x86/kernel/acpi/madt_wakeup.c | 4 ++++
> include/linux/cc_platform.h | 10 ----------
> kernel/cpu.c | 2 +-
> 4 files changed, 5 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c
> index eeec9986570e..f07c3bb7deab 100644
> --- a/arch/x86/coco/core.c
> +++ b/arch/x86/coco/core.c
> @@ -20,7 +20,6 @@ static bool noinstr intel_cc_platform_has(enum cc_attr attr)
> {
> switch (attr) {
> case CC_ATTR_GUEST_UNROLL_STRING_IO:
> - case CC_ATTR_HOTPLUG_DISABLED:
> case CC_ATTR_GUEST_MEM_ENCRYPT:
> case CC_ATTR_MEM_ENCRYPT:
> return true;
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> index 1b9747bfd5b9..15bdf10b1393 100644
> --- a/arch/x86/kernel/acpi/madt_wakeup.c
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -1,4 +1,5 @@
> #include <linux/acpi.h>
> +#include <linux/cpu.h>
> #include <asm/apic.h>
>
> /* Physical address of the Multiprocessor Wakeup Structure mailbox */
> @@ -74,6 +75,9 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>
> acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
>
> + /* Disable CPU onlining/offlining */
> + cpu_hotplug_not_supported();
> +
> apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
>
> return 0;
> diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
> index cb0d6cd1c12f..d08dd65b5c43 100644
> --- a/include/linux/cc_platform.h
> +++ b/include/linux/cc_platform.h
> @@ -80,16 +80,6 @@ enum cc_attr {
> * using AMD SEV-SNP features.
> */
> CC_ATTR_GUEST_SEV_SNP,
> -
> - /**
> - * @CC_ATTR_HOTPLUG_DISABLED: Hotplug is not supported or disabled.
> - *
> - * The platform/OS is running as a guest/virtual machine does not
> - * support CPU hotplug feature.
> - *
> - * Examples include TDX Guest.
> - */
> - CC_ATTR_HOTPLUG_DISABLED,
> };
>
> #ifdef CONFIG_ARCH_HAS_CC_PLATFORM
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index cf536fe1a88a..9d4279476b40 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1522,7 +1522,7 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
> * If the platform does not support hotplug, report it explicitly to
> * differentiate it from a transient offlining failure.
> */
> - if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED) || !cpu_hotplug_supported)
> + if (!cpu_hotplug_supported)
> return -EOPNOTSUPP;
> if (cpu_hotplug_disabled)
> return -EBUSY;
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer
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