ARM: SMP: use idmap_pgd for mapping MMU enable during secondary booting

The ARM SMP booting code allocates a temporary set of page tables
containing an identity mapping of the kernel image and provides this
to secondary CPUs for initial booting.

In reality, we only need to include the __turn_mmu_on function in the
identity mapping since the rest of the kernel is executing from virtual
addresses after this point.

This patch adds __turn_mmu_on to the .idmap.text section, allowing the
SMP booting code to use the idmap_pgd directly and not have to populate
its own set of page table.

As a result of this patch, we can make the identity_mapping_add function
static (since it is only used within mm/idmap.c) and also remove the
identity_mapping_del function. The identity map population is moved to
an early initcall so that it is setup in time for secondary CPU bringup.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

2 files changed, 4 insertions, 31 deletions

diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index 43e3aa3b0573..64e9943ea4f0 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S
@@ -398,7 +398,8 @@ ENDPROC(__enable_mmu)
  * other registers depend on the function called upon completion
  */
 	.align	5
-__turn_mmu_on:
+	.pushsection	.idmap.text, "ax"
+ENTRY(__turn_mmu_on)
 	mov	r0, r0
 	mcr	p15, 0, r0, c1, c0, 0		@ write control reg
 	mrc	p15, 0, r3, c0, c0, 0		@ read id reg
@@ -407,6 +408,7 @@ __turn_mmu_on:
 	mov	pc, r3
 __turn_mmu_on_end:
 ENDPROC(__turn_mmu_on)
+	.popsection
 
 
 #ifdef CONFIG_SMP_ON_UP
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 8afadda37459..76ff28d87bf3 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -62,7 +62,6 @@ int __cpuinit __cpu_up(unsigned int cpu)
 {
 	struct cpuinfo_arm *ci = &per_cpu(cpu_data, cpu);
 	struct task_struct *idle = ci->idle;
-	pgd_t *pgd;
 	int ret;
 
 	/*
@@ -85,29 +84,11 @@ int __cpuinit __cpu_up(unsigned int cpu)
 	}
 
 	/*
-	 * 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);
-	if (!pgd)
-		return -ENOMEM;
-
-	if (PHYS_OFFSET != PAGE_OFFSET) {
-#ifndef CONFIG_HOTPLUG_CPU
-		identity_mapping_add(pgd, __pa(__init_begin), __pa(__init_end));
-#endif
-		identity_mapping_add(pgd, __pa(_stext), __pa(_etext));
-		identity_mapping_add(pgd, __pa(_sdata), __pa(_edata));
-	}
-
-	/*
 	 * We need to tell the secondary core where to find
 	 * its stack and the page tables.
 	 */
 	secondary_data.stack = task_stack_page(idle) + THREAD_START_SP;
-	secondary_data.pgdir = virt_to_phys(pgd);
+	secondary_data.pgdir = virt_to_phys(idmap_pgd);
 	secondary_data.swapper_pg_dir = virt_to_phys(swapper_pg_dir);
 	__cpuc_flush_dcache_area(&secondary_data, sizeof(secondary_data));
 	outer_clean_range(__pa(&secondary_data), __pa(&secondary_data + 1));
@@ -143,16 +124,6 @@ int __cpuinit __cpu_up(unsigned int cpu)
 	secondary_data.stack = NULL;
 	secondary_data.pgdir = 0;
 
-	if (PHYS_OFFSET != PAGE_OFFSET) {
-#ifndef CONFIG_HOTPLUG_CPU
-		identity_mapping_del(pgd, __pa(__init_begin), __pa(__init_end));
-#endif
-		identity_mapping_del(pgd, __pa(_stext), __pa(_etext));
-		identity_mapping_del(pgd, __pa(_sdata), __pa(_edata));
-	}
-
-	pgd_free(&init_mm, pgd);
-
 	return ret;
 }