x86/vdso32/syscall.S: Do not load __USER32_DS to %ss

dvlasenk · Ingo Molnar · commit e7d6eefaaa44 · 2015-03-31T10:45:15.000+02:00
This vDSO code only gets used by 64-bit kernels, not 32-bit ones. On 64-bit kernels, the data segment is the same for 32-bit and 64-bit userspace, and the SYSRET instruction loads %ss with its selector. So there's no need to repeat it by hand. Segment loads are somewhat expensive: tens of cycles. Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com> [ Removed unnecessary comment. ] Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Alexei Starovoitov <ast@plumgrid.com> Cc: Andy Lutomirski <luto@amacapital.net> 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/63da6d778f69fd0f1345d9287f6764d58be519fa.1427482099.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/vdso/vdso32/syscall.S b/arch/x86/vdso/vdso32/syscall.S
@@ -19,8 +19,6 @@ __kernel_vsyscall:
 .Lpush_ebp:
 	movl	%ecx, %ebp
 	syscall
-	movl	$__USER32_DS, %ecx
-	movl	%ecx, %ss
 	movl	%ebp, %ecx
 	popl	%ebp
 .Lpop_ebp:
