[PATCH 1/7] ARM: Pass cpu number to secondary_start_kernel

Keith Packard
2021-09-07T22:00:53Z

Instead of pulling the CPU value out of the thread_info struct, pass
it as an argument. When first initializing secondary processors, this
is done by stashing the value in the secondary_data struct. When
restarting idle processors, the previous CPU value is passed.

Because the cpu is now known at the top of secondary_start_kernel, the
per_cpu_offset value can now be set at this point, instead of in
cpu_init where it was also incorrectly setting the per_cpu_offset for
the boot processor before that value had been computed.

Signed-off-by: Keith Packard <keithpac@amazon.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm/include/asm/smp.h | 3 ++-
arch/arm/kernel/head-nommu.S | 1 +
arch/arm/kernel/head.S | 1 +
arch/arm/kernel/setup.c | 6 ------
arch/arm/kernel/smp.c | 14 +++++++++-----
5 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/arch/arm/include/asm/smp.h b/arch/arm/include/asm/smp.h
index 5d508f5d56c4..86a7fd721556 100644
--- a/arch/arm/include/asm/smp.h
+++ b/arch/arm/include/asm/smp.h
@@ -48,7 +48,7 @@ extern void set_smp_ipi_range(int ipi_base, int nr_ipi);
* Called from platform specific assembly code, this is the
* secondary CPU entry point.
*/
-asmlinkage void secondary_start_kernel(void);
+asmlinkage void secondary_start_kernel(unsigned int cpu);

/*
@@ -61,6 +61,7 @@ struct secondary_data {
};
unsigned long swapper_pg_dir;
void *stack;
+ unsigned int cpu;
};
extern struct secondary_data secondary_data;
extern void secondary_startup(void);
diff --git a/arch/arm/kernel/head-nommu.S b/arch/arm/kernel/head-nommu.S
index 0fc814bbc34b..5aa8ef42717f 100644
--- a/arch/arm/kernel/head-nommu.S
+++ b/arch/arm/kernel/head-nommu.S
@@ -114,6 +114,7 @@ ENTRY(secondary_startup)
add r12, r12, r10
ret r12
1: bl __after_proc_init
+ ldr r0, [r7, #16] @ set up cpu number
ldr sp, [r7, #12] @ set up the stack pointer
mov fp, #0
b secondary_start_kernel
diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index 7f62c5eccdf3..0e541af738e2 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S
@@ -394,6 +394,7 @@ ENDPROC(secondary_startup_arm)

ENTRY(__secondary_switched)
ldr_l r7, secondary_data + 12 @ get secondary_data.stack
+ ldr_l r0, secondary_data + 16 @ get secondary_data.cpu
mov sp, r7
mov fp, #0
b secondary_start_kernel
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 73ca7797b92f..ca0201635fac 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -532,12 +532,6 @@ void notrace cpu_init(void)
BUG();
}

- /*
- * This only works on resume and secondary cores. For booting on the
- * boot cpu, smp_prepare_boot_cpu is called after percpu area setup.
- */
- set_my_cpu_offset(per_cpu_offset(cpu));
-
cpu_proc_init();

/*
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 74679240a9d8..55cb1689a4b3 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -153,6 +153,7 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
secondary_data.pgdir = virt_to_phys(idmap_pgd);
secondary_data.swapper_pg_dir = get_arch_pgd(swapper_pg_dir);
#endif
+ secondary_data.cpu = cpu;
sync_cache_w(&secondary_data);

/*
@@ -373,11 +374,14 @@ void arch_cpu_idle_dead(void)
* cpu initialisation. There's some initialisation which needs
* to be repeated to undo the effects of taking the CPU offline.
*/
- __asm__("mov sp, %0\n"
+ __asm__("mov r0, %1\n"
+ " mov sp, %0\n"
" mov fp, #0\n"
" b secondary_start_kernel"
:
- : "r" (task_stack_page(current) + THREAD_SIZE - 8));
+ : "r" (task_stack_page(current) + THREAD_SIZE - 8),
+ "r" (cpu)
+ : "r0");
}
#endif /* CONFIG_HOTPLUG_CPU */

@@ -400,10 +404,11 @@ static void smp_store_cpu_info(unsigned int cpuid)
* This is the secondary CPU boot entry. We're using this CPUs
* idle thread stack, but a set of temporary page tables.
*/
-asmlinkage void secondary_start_kernel(void)
+asmlinkage void secondary_start_kernel(unsigned int cpu)
{
struct mm_struct *mm = &init_mm;
- unsigned int cpu;
+
+ set_my_cpu_offset(per_cpu_offset(cpu));

secondary_biglittle_init();

@@ -420,7 +425,6 @@ asmlinkage void secondary_start_kernel(void)
* All kernel threads share the same mm context; grab a
* reference and switch to it.
*/
- cpu = smp_processor_id();
mmgrab(mm);
current->active_mm = mm;
cpumask_set_cpu(cpu, mm_cpumask(mm));
--
2.33.0