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>

4 files changed, 6 insertions, 66 deletions

diff --git a/arch/arm/include/asm/idmap.h b/arch/arm/include/asm/idmap.h
index 62e3d19c9ad..bf863edb517 100644
--- a/arch/arm/include/asm/idmap.h
+++ b/arch/arm/include/asm/idmap.h
@@ -9,9 +9,6 @@
 
 extern pgd_t *idmap_pgd;
 
-void identity_mapping_add(pgd_t *, unsigned long, unsigned long);
-void identity_mapping_del(pgd_t *, unsigned long, unsigned long);
-
 void setup_mm_for_reboot(void);
 
 #endif  /* __ASM_IDMAP_H */
diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index 43e3aa3b057..64e9943ea4f 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 8afadda3745..76ff28d87bf 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;
 }
 
diff --git a/arch/arm/mm/idmap.c b/arch/arm/mm/idmap.c
index b01760e6da1..660f1bc68f9 100644
--- a/arch/arm/mm/idmap.c
+++ b/arch/arm/mm/idmap.c
@@ -32,7 +32,7 @@ static void idmap_add_pud(pgd_t *pgd, unsigned long addr, unsigned long end,
         } while (pud++, addr = next, addr != end);
 }
 
-void identity_mapping_add(pgd_t *pgd, unsigned long addr, unsigned long end)
+static void identity_mapping_add(pgd_t *pgd, unsigned long addr, unsigned long end)
 {
         unsigned long prot, next;
 
@@ -47,36 +47,6 @@ void identity_mapping_add(pgd_t *pgd, unsigned long addr, unsigned long end)
         } while (pgd++, addr = next, addr != end);
 }
 
-#ifdef CONFIG_SMP
-static void idmap_del_pmd(pud_t *pud, unsigned long addr, unsigned long end)
-{
-        pmd_t *pmd = pmd_offset(pud, addr);
-        pmd_clear(pmd);
-}
-
-static void idmap_del_pud(pgd_t *pgd, unsigned long addr, unsigned long end)
-{
-        pud_t *pud = pud_offset(pgd, addr);
-        unsigned long next;
-
-        do {
-                next = pud_addr_end(addr, end);
-                idmap_del_pmd(pud, addr, next);
-        } while (pud++, addr = next, addr != end);
-}
-
-void identity_mapping_del(pgd_t *pgd, unsigned long addr, unsigned long end)
-{
-        unsigned long next;
-
-        pgd += pgd_index(addr);
-        do {
-                next = pgd_addr_end(addr, end);
-                idmap_del_pud(pgd, addr, next);
-        } while (pgd++, addr = next, addr != end);
-}
-#endif
-
 extern char  __idmap_text_start[], __idmap_text_end[];
 
 static int __init init_static_idmap(void)
@@ -97,7 +67,7 @@ static int __init init_static_idmap(void)
 
         return 0;
 }
-arch_initcall(init_static_idmap);
+early_initcall(init_static_idmap);
 
 /*
  * In order to soft-boot, we need to switch to a 1:1 mapping for the