• Tejun Heo's avatar
    x86: make lazy %gs optional on x86_32 · ccbeed3a
    Tejun Heo authored
    
    
    Impact: pt_regs changed, lazy gs handling made optional, add slight
            overhead to SAVE_ALL, simplifies error_code path a bit
    
    On x86_32, %gs hasn't been used by kernel and handled lazily.  pt_regs
    doesn't have place for it and gs is saved/loaded only when necessary.
    In preparation for stack protector support, this patch makes lazy %gs
    handling optional by doing the followings.
    
    * Add CONFIG_X86_32_LAZY_GS and place for gs in pt_regs.
    
    * Save and restore %gs along with other registers in entry_32.S unless
      LAZY_GS.  Note that this unfortunately adds "pushl $0" on SAVE_ALL
      even when LAZY_GS.  However, it adds no overhead to common exit path
      and simplifies entry path with error code.
    
    * Define different user_gs accessors depending on LAZY_GS and add
      lazy_save_gs() and lazy_load_gs() which are noop if !LAZY_GS.  The
      lazy_*_gs() ops are used to save, load and clear %gs lazily.
    
    * Define ELF_CORE_COPY_KERNEL_REGS() which always read %gs directly.
    
    xen and lguest changes need to be verified.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Cc: Jeremy Fitzhardinge <jeremy@xensource.com>
    Cc: Rusty Russell <rusty@rustcorp.com.au>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    ccbeed3a
system.h 13.4 KB