LoongArch: Give more information if kmem access failed

If memory access such as copy_{from, to}_kernel_nofault() failed, its
users do not know what happened, so it is very useful to print the
exception code for such cases. Furthermore, it is better to print the
caller function to know where is the entry.

Here are the low level call chains:

  copy_from_kernel_nofault()
    copy_from_kernel_nofault_loop()
      __get_kernel_nofault()

  copy_to_kernel_nofault()
    copy_to_kernel_nofault_loop()
      __put_kernel_nofault()

Cc: stable@vger.kernel.org
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

Author: seehearfeel

arch/loongarch/include/asm/uaccess.h

@@ -253,8 +253,13 @@ do {									\
 									\
 	__get_kernel_common(*((type *)(dst)), sizeof(type),		\
 			    (__force type *)(src));			\
-	if (unlikely(__gu_err))						\
+	if (unlikely(__gu_err))	{					\
+		pr_info("%s: memory access failed, ecode 0x%x\n",	\
+			__func__, read_csr_excode());			\
+		pr_info("%s: the caller is %pS\n",			\
+			__func__, __builtin_return_address(0));		\
 		goto err_label;						\
+	}								\
 } while (0)
 
 #define __put_kernel_nofault(dst, src, type, err_label)			\
@@ -264,8 +269,13 @@ do {									\
 									\
 	__pu_val = *(__force type *)(src);				\
 	__put_kernel_common(((type *)(dst)), sizeof(type));		\
-	if (unlikely(__pu_err))						\
+	if (unlikely(__pu_err))	{					\
+		pr_info("%s: memory access failed, ecode 0x%x\n",	\
+			__func__, read_csr_excode());			\
+		pr_info("%s: the caller is %pS\n",			\
+			__func__, __builtin_return_address(0));		\
 		goto err_label;						\
+	}								\
 } while (0)
 
 extern unsigned long __copy_user(void *to, const void *from, __kernel_size_t n);