TTBR0 and switch_mm

switch_mm(struct mm_struct *prev, struct mm_struct *next, struct task_struct *tsk)

    cpu_switch_mm(next->pgd, next);

#define cpu_switch_mm(pgd,mm) cpu_do_switch_mm(virt_to_phys(pgd),mm)

#define cpu_do_switch_mm processor.switch_mm

proc-v7-2level.S
//cpu_v7_switch_mm(pgd_phys, tsk)
ENTRY(cpu_v7_switch_mm)
#ifdef CONFIG_MMU
mov r2, #0
ldr r1, [r1, #MM_CONTEXT_ID] @ get mm->context.id
ALT_SMP(orr r0, r0, #TTB_FLAGS_SMP)
ALT_UP(orr r0, r0, #TTB_FLAGS_UP)
#ifdef CONFIG_ARM_ERRATA_430973
mcr p15, 0, r2, c7, c5, 6 @ flush BTAC/BTB
#endif
#ifdef CONFIG_ARM_ERRATA_754322
dsb
#endif
mcr p15, 0, r2, c13, c0, 1 @ set reserved context ID
isb
1: mcr p15, 0, r0, c2, c0, 0 @ set TTB 0
isb
#ifdef CONFIG_ARM_ERRATA_754322
dsb
#endif
mcr p15, 0, r1, c13, c0, 1 @ set context ID
isb
#endif
mov pc, lr
ENDPROC(cpu_v7_switch_mm)