arm64: smp: remove stack from secondary_data

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@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Suzuki Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20210520115031.18509-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

Author: mrutland-arm

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;
 };

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));

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

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);