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x86/percpu: Cure per CPU madness on UP

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On UP builds Sparse complains rightfully about accesses to cpu_info with
per CPU accessors:

  cacheinfo.c:282:30: sparse: warning: incorrect type in initializer (different address spaces)
  cacheinfo.c:282:30: sparse:    expected void const [noderef] __percpu *__vpp_verify
  cacheinfo.c:282:30: sparse:    got unsigned int *

The reason is that on UP builds cpu_info which is a per CPU variable on SMP
is mapped to boot_cpu_info which is a regular variable. There is a hideous
accessor cpu_data() which tries to hide this, but it's not sufficient as
some places require raw accessors and generates worse code than the regular
per CPU accessors.

Waste sizeof(struct x86_cpuinfo) memory on UP and provide the per CPU
cpu_info unconditionally. This requires to update the CPU info on the boot
CPU as SMP does. (Ab)use the weakly defined smp_prepare_boot_cpu() function
and implement exactly that.

This allows to use regular per CPU accessors uncoditionally and paves the
way to remove the cpu_data() hackery.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240304005104.622511517@linutronix.de
This commit is contained in:
Thomas Gleixner 2024-03-04 11:12:23 +01:00 committed by Ingo Molnar
parent 712610725c
commit 71eb4893cf
4 changed files with 13 additions and 9 deletions
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5
arch/x86/include/asm/processor.h
View File

@ -185,13 +185,8 @@ extern struct cpuinfo_x86 new_cpu_data;
extern __u32 cpu_caps_cleared[NCAPINTS + NBUGINTS];
extern __u32 cpu_caps_set[NCAPINTS + NBUGINTS];
#ifdef CONFIG_SMP
DECLARE_PER_CPU_READ_MOSTLY(struct cpuinfo_x86, cpu_info);
#define cpu_data(cpu) per_cpu(cpu_info, cpu)
#else
#define cpu_info boot_cpu_data
#define cpu_data(cpu) boot_cpu_data
#endif
extern const struct seq_operations cpuinfo_op;

3
arch/x86/kernel/cpu/common.c
View File

@ -70,6 +70,9 @@
#include "cpu.h"
DEFINE_PER_CPU_READ_MOSTLY(struct cpuinfo_x86, cpu_info);
EXPORT_PER_CPU_SYMBOL(cpu_info);
u32 elf_hwcap2 __read_mostly;
/* Number of siblings per CPU package */

10
arch/x86/kernel/setup.c
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@ -1211,6 +1211,16 @@ void __init i386_reserve_resources(void)
#endif /* CONFIG_X86_32 */
#ifndef CONFIG_SMP
void __init smp_prepare_boot_cpu(void)
{
struct cpuinfo_x86 *c = &cpu_data(0);
*c = boot_cpu_data;
c->initialized = true;
}
#endif
static struct notifier_block kernel_offset_notifier = {
.notifier_call = dump_kernel_offset
};

4
arch/x86/kernel/smpboot.c
View File

@ -101,10 +101,6 @@ EXPORT_PER_CPU_SYMBOL(cpu_core_map);
DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_die_map);
EXPORT_PER_CPU_SYMBOL(cpu_die_map);
/* Per CPU bogomips and other parameters */
DEFINE_PER_CPU_READ_MOSTLY(struct cpuinfo_x86, cpu_info);
EXPORT_PER_CPU_SYMBOL(cpu_info);
/* CPUs which are the primary SMT threads */
struct cpumask __cpu_primary_thread_mask __read_mostly;