[tip:x86/asm] x86/asm/entry/64: Remove unused thread_struct:: usersp

[tip-bot for Denys Vlasenko <tipbot@zytor.com>]

Commit-ID:  245214a155c711764b3853189441c9f8aeb058b3
Gitweb:     http://git.kernel.org/tip/245214a155c711764b3853189441c9f8aeb058b3
Author:     Denys Vlasenko <dvlasenk@redhat.com>
AuthorDate: Tue, 10 Mar 2015 11:45:07 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 10 Mar 2015 13:56:11 +0100

x86/asm/entry/64: Remove unused thread_struct::usersp

All manipulations of PER_CPU(old_rsp) in C code are removed:
it is not used on SYSRET return, so storing anything there is
pointless.

This also allows us to get rid of thread_struct::usersp,
which was needed only to set PER_CPU(old_rsp) for correct
return from fork/clone.

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

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Borislav Petkov <bp@alien8.de>
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/1425984307-2143-2-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/processor.h | 6 ------
 arch/x86/kernel/entry_64.S       | 4 ++--
 arch/x86/kernel/process_64.c     | 5 -----
 3 files changed, 2 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 48a61c1..c77605d 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -478,7 +478,6 @@ struct thread_struct {
 #ifdef CONFIG_X86_32
 	unsigned long		sysenter_cs;
 #else
-	unsigned long		usersp;	/* Copy from PDA */
 	unsigned short		es;
 	unsigned short		ds;
 	unsigned short		fsindex;
@@ -894,11 +893,6 @@ 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/entry_64.S b/arch/x86/kernel/entry_64.S
index d86788c..9e37b36 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -303,7 +303,7 @@ int_ret_from_sys_call_fixup:
 	FIXUP_TOP_OF_STACK %r11
 	jmp int_ret_from_sys_call
 
-	/* Do syscall tracing */
+	/* Do syscall entry tracing */
 tracesys:
 	movq %rsp, %rdi
 	movq $AUDIT_ARCH_X86_64, %rsi
@@ -343,7 +343,7 @@ tracesys_phase2:
 
 /*
  * Syscall return path ending with IRET.
- * Has correct top of stack, but partial stack frame.
+ * Has correct iret frame.
  */
 GLOBAL(int_ret_from_sys_call)
 	DISABLE_INTERRUPTS(CLBR_NONE)
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index e8c124a..14df2be 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -161,7 +161,6 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
 	p->thread.sp0 = (unsigned long)task_stack_page(p) + THREAD_SIZE;
 	childregs = task_pt_regs(p);
 	p->thread.sp = (unsigned long) childregs;
-	p->thread.usersp = me->thread.usersp;
 	set_tsk_thread_flag(p, TIF_FORK);
 	p->thread.io_bitmap_ptr = NULL;
 
@@ -235,10 +234,8 @@ start_thread_common(struct pt_regs *regs, unsigned long new_ip,
 	loadsegment(es, _ds);
 	loadsegment(ds, _ds);
 	load_gs_index(0);
-	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;
@@ -398,8 +395,6 @@ __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);
 
 	/*