[PATCH v4 1/7] ARM: Pass cpu number to secondary_start_kernel

[Keith Packard <keithpac@amazon.com>]

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