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x86: make lazy %gs optional on x86_32

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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: Tejun Heo <tj@kernel.org>
Cc: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>

Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Tejun Heo
2009-02-09 22:17:40 +09:00
committed by Ingo Molnar
parent d9a89a26e0
commit ccbeed3a05
11 changed files with 158 additions and 40 deletions
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12
arch/x86/include/asm/system.h
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@@ -186,10 +186,20 @@ extern void native_load_gs_index(unsigned);
* x86_32 user gs accessors.
*/
#ifdef CONFIG_X86_32
#ifdef CONFIG_X86_32_LAZY_GS
#define get_user_gs(regs) (u16)({unsigned long v; savesegment(gs, v); v;})
#define set_user_gs(regs, v) loadsegment(gs, (unsigned long)(v))
#define task_user_gs(tsk) ((tsk)->thread.gs)
#endif
#define lazy_save_gs(v) savesegment(gs, (v))
#define lazy_load_gs(v) loadsegment(gs, (v))
#else /* X86_32_LAZY_GS */
#define get_user_gs(regs) (u16)((regs)->gs)
#define set_user_gs(regs, v) do { (regs)->gs = (v); } while (0)
#define task_user_gs(tsk) (task_pt_regs(tsk)->gs)
#define lazy_save_gs(v) do { } while (0)
#define lazy_load_gs(v) do { } while (0)
#endif /* X86_32_LAZY_GS */
#endif /* X86_32 */
static inline unsigned long get_limit(unsigned long segment)
{