Commit 71eb4893 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Ingo Molnar
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x86/percpu: Cure per CPU madness on UP 



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: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240304005104.622511517@linutronix.de
parent 71261072

arch/x86/include/asm/processor.h

+0 −5
Original line number Diff line number Diff line
@@ -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;

arch/x86/kernel/cpu/common.c

+3 −0
Original line number Diff line number Diff line
@@ -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 */

arch/x86/kernel/setup.c

+10 −0
Original line number Diff line number Diff line
@@ -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

};

arch/x86/kernel/smpboot.c

+0 −4
Original line number Diff line number Diff line
@@ -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;