From: James Morse james.morse@arm.com
mainline inclusion from mainline-v6.8-rc1 commit b0c69e1214bc20960c2ca68317b968e2a2057ed5 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I8XMTL CVE: NA
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Three of the five ACPI architectures create sysfs entries using register_cpu() for present CPUs, whereas arm64, riscv and all GENERIC_CPU_DEVICES do this for possible CPUs.
Registering a CPU is what causes them to show up in sysfs.
It makes very little sense to register all possible CPUs. Registering a CPU is what triggers the udev notifications allowing user-space to react to newly added CPUs.
To allow all five ACPI architectures to use GENERIC_CPU_DEVICES, change it to use for_each_present_cpu().
Making the ACPI architectures use GENERIC_CPU_DEVICES is a pre-requisite step to centralise their register_cpu() logic, before moving it into the ACPI processor driver. When we add support for register CPUs from ACPI in a later patch, we will avoid registering CPUs in this path.
Of the ACPI architectures that register possible CPUs, arm64 and riscv do not support making possible CPUs present as they use the weak 'always fails' version of arch_register_cpu().
Only two of the eight architectures that use GENERIC_CPU_DEVICES have a distinction between present and possible CPUs.
The following architectures use GENERIC_CPU_DEVICES but are not SMP, so possible == present: * m68k * microblaze * nios2
The following architectures use GENERIC_CPU_DEVICES and consider possible == present: * csky: setup_smp() * processor_probe() sets possible for all CPUs and present for all CPUs except the boot cpu, which will have been done by init/main.c::start_kernel().
um appears to be a subarchitecture of x86.
The remaining architecture using GENERIC_CPU_DEVICES are: * openrisc and hexagon: where smp_init_cpus() makes all CPUs < NR_CPUS possible, whereas smp_prepare_cpus() only makes CPUs < setup_max_cpus present.
After this change, openrisc and hexagon systems that use the max_cpus command line argument would not see the other CPUs present in sysfs. This should not be a problem as these CPUs can't be brought online as _cpu_up() checks cpu_present().
After this change, only CPUs which are present appear in sysfs.
Signed-off-by: James Morse james.morse@arm.com Reviewed-by: Jonathan Cameron Jonathan.Cameron@huawei.com Reviewed-by: Gavin Shan gshan@redhat.com Signed-off-by: "Russell King (Oracle)" rmk+kernel@armlinux.org.uk Reviewed-by: Thomas Gleixner tglx@linutronix.de Link: https://lore.kernel.org/r/E1r5R36-00Csz0-Px@rmk-PC.armlinux.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: liwei liwei728@huawei.com --- drivers/base/cpu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c index 548491de818e..13359712e069 100644 --- a/drivers/base/cpu.c +++ b/drivers/base/cpu.c @@ -533,7 +533,7 @@ static void __init cpu_dev_register_generic(void) #ifdef CONFIG_GENERIC_CPU_DEVICES int i;
- for_each_possible_cpu(i) { + for_each_present_cpu(i) { if (register_cpu(&per_cpu(cpu_devices, i), i)) panic("Failed to register CPU device"); }