From 1037e4c53e851682ff8d1ab656567a4d5a333c93 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Fri, 14 Jun 2024 12:58:48 +0300 Subject: cpu/hotplug: Add support for declaring CPU offlining not supported The ACPI MADT mailbox wakeup method doesn't allow to offline a CPU after it has been woken up. Currently, offlining is 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. The MADT wakeup can be implemented outside of a confidential computing environment. Offline support is a property of the wakeup method, not the CoCo implementation. Introduce cpu_hotplug_disable_offlining() that can be called to indicate that CPU offlining should be disabled. This function is going to replace CC_ATTR_HOTPLUG_DISABLED for ACPI MADT wakeup method. Signed-off-by: Kirill A. Shutemov Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Thomas Gleixner Tested-by: Tao Liu Link: https://lore.kernel.org/r/20240614095904.1345461-4-kirill.shutemov@linux.intel.com --- kernel/cpu.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index 563877d6c28b..4c15b478e2bc 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -483,6 +483,8 @@ static int cpu_hotplug_disabled; DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock); +static bool cpu_hotplug_offline_disabled __ro_after_init; + void cpus_read_lock(void) { percpu_down_read(&cpu_hotplug_lock); @@ -542,6 +544,14 @@ static void lockdep_release_cpus_lock(void) rwsem_release(&cpu_hotplug_lock.dep_map, _THIS_IP_); } +/* Declare CPU offlining not supported */ +void cpu_hotplug_disable_offlining(void) +{ + cpu_maps_update_begin(); + cpu_hotplug_offline_disabled = true; + cpu_maps_update_done(); +} + /* * Wait for currently running CPU hotplug operations to complete (if any) and * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects @@ -1471,7 +1481,8 @@ 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)) + if (cc_platform_has(CC_ATTR_HOTPLUG_DISABLED) || + cpu_hotplug_offline_disabled) return -EOPNOTSUPP; if (cpu_hotplug_disabled) return -EBUSY; -- cgit v1.2.3 From 66e48e491d1e1a0f243ebfcb9639b23de1a5db5e Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Fri, 14 Jun 2024 12:58:49 +0300 Subject: cpu/hotplug, x86/acpi: Disable CPU offlining for ACPI MADT wakeup ACPI MADT doesn't allow to offline a CPU after it has been woken up. Currently, CPU hotplug is 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. Any platform that uses ACPI MADT wakeup method cannot offline CPU. Disable CPU offlining on ACPI MADT wakeup enumeration. This has no visible effects for users: currently, TDX guest is the only platform that uses the ACPI MADT wakeup method. Signed-off-by: Kirill A. Shutemov Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Thomas Gleixner Acked-by: Rafael J. Wysocki Tested-by: Tao Liu Link: https://lore.kernel.org/r/20240614095904.1345461-5-kirill.shutemov@linux.intel.com --- kernel/cpu.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index 4c15b478e2bc..a609385c7f99 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -1481,8 +1481,7 @@ 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_offline_disabled) + if (cpu_hotplug_offline_disabled) return -EOPNOTSUPP; if (cpu_hotplug_disabled) return -EBUSY; -- cgit v1.2.3