按指令集手册的说明，修改ASID和TTBR的同步更新。

libcpu/arm/cortex-a/start_gcc.S

@@ -176,7 +176,11 @@ bss_loop:
 #ifdef RT_USING_USERSPACE
     ldr r0, =MMUTable     /* vaddr    */
     add r0, r5            /* to paddr */
+#ifdef RT_LWP_ENABLE_ASID
+    bl  rt_hw_mmu_switch_kernel
+#else
     bl  rt_hw_mmu_switch
+#endif
 #else
     bl rt_hw_mmu_init
 #endif
@@ -270,13 +274,19 @@ rt_hw_set_process_id:
 #ifdef RT_LWP_ENABLE_ASID
 .global rt_hw_mmu_switch
 rt_hw_mmu_switch:
+    mov r3, #0
+    mcr p15, 0, r3, c13, c0, 1   /* set contextid = 0, for synchronization*/ 
+    isb
+    
     orr r0, #0x18
     mcr p15, 0, r0, c2, c0, 0    /* ttbr0   write r0 to ttbr0*/
+    isb
 
-    and r2, r1, #0xff
-    mov r1, r1, LSL #0x8
-    orr r1, r1, r2                /* r1 = (asid << 8) | (asid & 0xFFUL) */
+    mov r1, r1, LSL #0x8         
+    and r2, r2, #0xff             
+    orr r1, r1, r2                /* contextid.PROCID = pid, contextid.ASID = asid*/
     mcr p15, 0, r1, c13, c0, 1    /* set contextid = r1*/ 
+    isb
 
     mcr p15, 0, r0, c7, c5, 0    /* iciallu */
     mcr p15, 0, r0, c7, c5, 6    /* bpiall */
@@ -284,6 +294,25 @@ rt_hw_mmu_switch:
     dsb
     isb
     mov pc, lr
+
+.global rt_hw_mmu_switch_kernel
+rt_hw_mmu_switch_kernel:
+    orr r0, #0x18
+    mcr p15, 0, r0, c2, c0, 0    /* ttbr0 */
+
+    /*  The nG bit of tlb entries of kernel is 0, 
+        so no need to update ASID, 
+        neither to flush TLB
+    */
+    ; mov r0, #0
+    ; mcr p15, 0, r0, c8, c7, 0
+    mcr p15, 0, r0, c7, c5, 0    /* iciallu */
+    mcr p15, 0, r0, c7, c5, 6    /* bpiall */
+
+    dsb
+    isb
+    mov pc, lr
+
 #else
 .global rt_hw_mmu_switch
 rt_hw_mmu_switch:
@@ -300,6 +329,7 @@ rt_hw_mmu_switch:
     isb
     mov pc, lr
 #endif
+
 .global rt_hw_mmu_tbl_get
 rt_hw_mmu_tbl_get:
     mrc p15, 0, r0, c2, c0, 0    /* ttbr0 */
@@ -641,8 +671,12 @@ rt_secondary_cpu_entry:
 after_enable_mmu_n:
     ldr     r0, =MMUTable
     add     r0, r5
+#ifdef RT_LWP_ENABLE_ASID
+    bl      rt_hw_mmu_switch_kernel
+#else
     bl      rt_hw_mmu_switch
 #endif
+#endif
 
 #ifdef RT_USING_FPU
     mov r4, #0xfffffff