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

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>

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 5abd9a535a2437b94951786402ce2a43943ded4e..3ac5092ec113b32f5c495ff4e627727017c5f334 100644 (file)
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -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,

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index e8c124a1f8851c359edf5ccfe67a22b5f86c3626..59696d76a4e33796023934be9b98d9e96c20d18e 100644 (file)
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -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);
 
        /*