[PATCH] ARM SMP: Add support for startup of secondary processors

Create a temporary page table to startup secondary processors.  This
page table must have a 1:1 virtual/physical mapping for the kernel
in addition to the standard mappings to ensure that the secondary
CPU can enable its MMU safely.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/head.S

@@ -2,6 +2,8 @@
  *  linux/arch/arm/kernel/head.S
  *
  *  Copyright (C) 1994-2002 Russell King
+ *  Copyright (c) 2003 ARM Limited
+ *  All Rights Reserved
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -165,6 +167,48 @@ __mmap_switched:
 	stmia	r6, {r0, r4}			@ Save control register values
 	b	start_kernel
 
+#if defined(CONFIG_SMP)
+	.type   secondary_startup, #function
+ENTRY(secondary_startup)
+	/*
+	 * Common entry point for secondary CPUs.
+	 *
+	 * Ensure that we're in SVC mode, and IRQs are disabled.  Lookup
+	 * the processor type - there is no need to check the machine type
+	 * as it has already been validated by the primary processor.
+	 */
+	msr	cpsr_c, #PSR_F_BIT | PSR_I_BIT | MODE_SVC
+	bl	__lookup_processor_type
+	movs	r10, r5				@ invalid processor?
+	moveq	r0, #'p'			@ yes, error 'p'
+	beq	__error
+
+	/*
+	 * Use the page tables supplied from  __cpu_up.
+	 */
+	adr	r4, __secondary_data
+	ldmia	r4, {r5, r6, r13}		@ address to jump to after
+	sub	r4, r4, r5			@ mmu has been enabled
+	ldr	r4, [r6, r4]			@ get secondary_data.pgdir
+	adr	lr, __enable_mmu		@ return address
+	add	pc, r10, #12			@ initialise processor
+						@ (return control reg)
+
+	/*
+	 * r6  = &secondary_data
+	 */
+ENTRY(__secondary_switched)
+	ldr	sp, [r6, #4]			@ get secondary_data.stack
+	mov	fp, #0
+	b	secondary_start_kernel
+
+	.type	__secondary_data, %object
+__secondary_data:
+	.long	.
+	.long	secondary_data
+	.long	__secondary_switched
+#endif /* defined(CONFIG_SMP) */
+
 
 
 /*

arch/arm/kernel/smp.c

@@ -24,6 +24,9 @@
 #include <asm/atomic.h>
 #include <asm/cacheflush.h>
 #include <asm/cpu.h>
+#include <asm/mmu_context.h>
+#include <asm/pgtable.h>
+#include <asm/pgalloc.h>
 #include <asm/processor.h>
 #include <asm/tlbflush.h>
 #include <asm/ptrace.h>
@@ -36,6 +39,13 @@
 cpumask_t cpu_present_mask;
 cpumask_t cpu_online_map;
 
+/*
+ * as from 2.5, kernels no longer have an init_tasks structure
+ * so we need some other way of telling a new secondary core
+ * where to place its SVC stack
+ */
+struct secondary_data secondary_data;
+
 /*
  * structures for inter-processor calls
  * - A collection of single bit ipi messages.
@@ -71,6 +81,8 @@ static DEFINE_SPINLOCK(smp_call_function_lock);
 int __init __cpu_up(unsigned int cpu)
 {
 	struct task_struct *idle;
+	pgd_t *pgd;
+	pmd_t *pmd;
 	int ret;
 
 	/*
@@ -83,10 +95,55 @@ int __init __cpu_up(unsigned int cpu)
 		return PTR_ERR(idle);
 	}
 
+	/*
+	 * Allocate initial page tables to allow the new CPU to
+	 * enable the MMU safely.  This essentially means a set
+	 * of our "standard" page tables, with the addition of
+	 * a 1:1 mapping for the physical address of the kernel.
+	 */
+	pgd = pgd_alloc(&init_mm);
+	pmd = pmd_offset(pgd, PHYS_OFFSET);
+	*pmd = __pmd((PHYS_OFFSET & PGDIR_MASK) |
+		     PMD_TYPE_SECT | PMD_SECT_AP_WRITE);
+
+	/*
+	 * We need to tell the secondary core where to find
+	 * its stack and the page tables.
+	 */
+	secondary_data.stack = (void *)idle->thread_info + THREAD_SIZE - 8;
+	secondary_data.pgdir = virt_to_phys(pgd);
+	wmb();
+
 	/*
 	 * Now bring the CPU into our world.
 	 */
 	ret = boot_secondary(cpu, idle);
+	if (ret == 0) {
+		unsigned long timeout;
+
+		/*
+		 * CPU was successfully started, wait for it
+		 * to come online or time out.
+		 */
+		timeout = jiffies + HZ;
+		while (time_before(jiffies, timeout)) {
+			if (cpu_online(cpu))
+				break;
+
+			udelay(10);
+			barrier();
+		}
+
+		if (!cpu_online(cpu))
+			ret = -EIO;
+	}
+
+	secondary_data.stack = 0;
+	secondary_data.pgdir = 0;
+
+	*pmd_offset(pgd, PHYS_OFFSET) = __pmd(0);
+	pgd_free(pgd);
+
 	if (ret) {
 		printk(KERN_CRIT "cpu_up: processor %d failed to boot\n", cpu);
 		/*
@@ -97,6 +154,56 @@ int __init __cpu_up(unsigned int cpu)
 	return ret;
 }
 
+/*
+ * This is the secondary CPU boot entry.  We're using this CPUs
+ * idle thread stack, but a set of temporary page tables.
+ */
+asmlinkage void __init secondary_start_kernel(void)
+{
+	struct mm_struct *mm = &init_mm;
+	unsigned int cpu = smp_processor_id();
+
+	printk("CPU%u: Booted secondary processor\n", cpu);
+
+	/*
+	 * All kernel threads share the same mm context; grab a
+	 * reference and switch to it.
+	 */
+	atomic_inc(&mm->mm_users);
+	atomic_inc(&mm->mm_count);
+	current->active_mm = mm;
+	cpu_set(cpu, mm->cpu_vm_mask);
+	cpu_switch_mm(mm->pgd, mm);
+	enter_lazy_tlb(mm, current);
+
+	cpu_init();
+
+	/*
+	 * Give the platform a chance to do its own initialisation.
+	 */
+	platform_secondary_init(cpu);
+
+	/*
+	 * Enable local interrupts.
+	 */
+	local_irq_enable();
+	local_fiq_enable();
+
+	calibrate_delay();
+
+	smp_store_cpu_info(cpu);
+
+	/*
+	 * OK, now it's safe to let the boot CPU continue
+	 */
+	cpu_set(cpu, cpu_online_map);
+
+	/*
+	 * OK, it's off to the idle thread for us
+	 */
+	cpu_idle();
+}
+
 /*
  * Called by both boot and secondaries to move global data into
  * per-processor storage.

include/asm-arm/smp.h

@@ -55,4 +55,18 @@ extern void smp_cross_call(cpumask_t callmap);
  */
 extern int boot_secondary(unsigned int cpu, struct task_struct *);
 
+/*
+ * Perform platform specific initialisation of the specified CPU.
+ */
+extern void platform_secondary_init(unsigned int cpu);
+
+/*
+ * Initial data for bringing up a secondary CPU.
+ */
+struct secondary_data {
+	unsigned long pgdir;
+	void *stack;
+};
+extern struct secondary_data secondary_data;
+
 #endif /* ifndef __ASM_ARM_SMP_H */