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x86/asm/entry/64: Simplify 'old_rsp' usage

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Remove all manipulations of PER_CPU(old_rsp) in C code:

 - it is not used on SYSRET return anymore, and system entries
   are atomic, so updating it from the fork and context switch
   paths is pointless.

 - Tweak a few related comments as well: we no longer have a
   "partial stack frame" on entry, ever.

Based on (split out of) patch from Denys Vlasenko.

Originally-from: Denys Vlasenko <dvlasenk@redhat.com>
Tested-by: Borislav Petkov <bp@alien8.de>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1426599779-8010-2-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Ingo Molnar 2015-03-17 14:42:59 +01:00
parent 33db1fd48a
commit 9854dd74c3
2 changed files with 0 additions and 7 deletions
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5
arch/x86/include/asm/processor.h
View file

@ -905,11 +905,6 @@ extern unsigned long thread_saved_pc(struct task_struct *tsk);
#define task_pt_regs(tsk) ((struct pt_regs *)(tsk)->thread.sp0 - 1)
extern unsigned long KSTK_ESP(struct task_struct *task);
/*
* User space RSP while inside the SYSCALL fast path
*/
DECLARE_PER_CPU(unsigned long, old_rsp);
#endif /* CONFIG_X86_64 */
extern void start_thread(struct pt_regs *regs, unsigned long new_ip,

2
arch/x86/kernel/process_64.c
View file

@ -238,7 +238,6 @@ start_thread_common(struct pt_regs *regs, unsigned long new_ip,
current->thread.usersp = new_sp;
regs->ip = new_ip;
regs->sp = new_sp;
this_cpu_write(old_rsp, new_sp);
regs->cs = _cs;
regs->ss = _ss;
regs->flags = X86_EFLAGS_IF;
@ -399,7 +398,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
* Switch the PDA and FPU contexts.
*/
prev->usersp = this_cpu_read(old_rsp);
this_cpu_write(old_rsp, next->usersp);
this_cpu_write(current_task, next_p);
/*