[PATCH 4/6] arm64: smp: remove stack from secondary_data

[Mark Rutland]

When we boot a secondary CPU, we pass it a task and a stack to use. As
the stack is always the task's stack, which can be derived from the
task, let's have the secondary CPU derive this itself and avoid passing
redundant information.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Cc: Ard Biesheuvel <ardb at kernel.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: James Morse <james.morse at arm.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Suzuki Poulose <suzuki.poulose at arm.com>
Cc: Will Deacon <will at kernel.org>
---
 arch/arm64/include/asm/smp.h    | 2 --
 arch/arm64/kernel/asm-offsets.c | 1 -
 arch/arm64/kernel/head.S        | 7 ++++---
 arch/arm64/kernel/smp.c         | 2 --
 4 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h
index 0e357757c0cc..fc55f5a57a06 100644
--- a/arch/arm64/include/asm/smp.h
+++ b/arch/arm64/include/asm/smp.h
@@ -73,12 +73,10 @@ asmlinkage void secondary_start_kernel(void);
 
 /*
  * Initial data for bringing up a secondary CPU.
- * @stack  - sp for the secondary CPU
  * @status - Result passed back from the secondary CPU to
  *           indicate failure.
  */
 struct secondary_data {
-	void *stack;
 	struct task_struct *task;
 	long status;
 };
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 0cb34ccb6e73..4a5e204c33af 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -99,7 +99,6 @@ int main(void)
   DEFINE(SOFTIRQ_SHIFT, SOFTIRQ_SHIFT);
   DEFINE(IRQ_CPUSTAT_SOFTIRQ_PENDING, offsetof(irq_cpustat_t, __softirq_pending));
   BLANK();
-  DEFINE(CPU_BOOT_STACK,	offsetof(struct secondary_data, stack));
   DEFINE(CPU_BOOT_TASK,		offsetof(struct secondary_data, task));
   BLANK();
   DEFINE(FTR_OVR_VAL_OFFSET,	offsetof(struct arm64_ftr_override, val));
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index cc2d45d54838..9be95e11367d 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -645,11 +645,12 @@ SYM_FUNC_START_LOCAL(__secondary_switched)
 	isb
 
 	adr_l	x0, secondary_data
-	ldr	x1, [x0, #CPU_BOOT_STACK]	// get secondary_data.stack
-	cbz	x1, __secondary_too_slow
-	mov	sp, x1
 	ldr	x2, [x0, #CPU_BOOT_TASK]
 	cbz	x2, __secondary_too_slow
+
+	ldr	x1, [x2, #TSK_STACK]
+	add	sp, x1, #THREAD_SIZE
+
 	msr	sp_el0, x2
 	scs_load x2, x3
 	setup_final_frame
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 92e83e8bac94..73625cc39574 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -120,7 +120,6 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 	 * page tables.
 	 */
 	secondary_data.task = idle;
-	secondary_data.stack = task_stack_page(idle) + THREAD_SIZE;
 	update_cpu_boot_status(CPU_MMU_OFF);
 
 	/* Now bring the CPU into our world */
@@ -141,7 +140,6 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 
 	pr_crit("CPU%u: failed to come online\n", cpu);
 	secondary_data.task = NULL;
-	secondary_data.stack = NULL;
 	status = READ_ONCE(secondary_data.status);
 	if (status == CPU_MMU_OFF)
 		status = READ_ONCE(__early_cpu_boot_status);
-- 
2.11.0