Why SAVE_ALL (for x86) macro in 2.6 loads __USER_DS to %ds

[rahul dev]

Guys,

  I was looking at the SAVE_ALL code for kernel 2.6.
I am confused why SAVE_ALL restores __USER_DS to ds and es ?

#define SAVE_ALL \
        cld; \
        pushl %fs; \
        pushl %es; \
        pushl %ds; \
        pushl %eax; \
        pushl %ebp; \
        pushl %edi; \
        pushl %esi; \
        pushl %edx; \
        pushl %ecx; \
        pushl %ebx; \
        movl $(__USER_DS), %edx; \   <---- why __USER_DS ?
        movl %edx, %ds; \
        movl %edx, %es; \
        movl $(__KERNEL_PDA), %edx; \
        movl %edx, %fs


If you look at the linux 2.4, it restores __KERNEL_DS in SAVE_ALL.
#define SAVE_ALL \
        cld; \
        pushl %es; \
        pushl %ds; \
        pushl %eax; \
        pushl %ebp; \
        pushl %edi; \
        pushl %esi; \
        pushl %edx; \
        pushl %ecx; \
        pushl %ebx; \
        movl $(__KERNEL_DS),%edx; \     <-- __KERNEL_DS is restored here.
        movl %edx,%ds; \
        movl %edx,%es;

Does anyone know why do we restore __USER_DS on context switch from user to 
kernel instead of __KERNEL_DS ?

thanks a lot for any help ...




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