Messages in this thread Patch in this message | | | Date | Tue, 31 Mar 2015 05:38:29 -0700 | From | tip-bot for Denys Vlasenko <> | Subject | [tip:x86/vdso] x86/vdso32/syscall.S: Do not load __USER32_DS to %ss |
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Commit-ID: e7d6eefaaa443130079d73cd05039d90b3db7a4a Gitweb: http://git.kernel.org/tip/e7d6eefaaa443130079d73cd05039d90b3db7a4a Author: Denys Vlasenko <dvlasenk@redhat.com> AuthorDate: Fri, 27 Mar 2015 11:48:17 -0700 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Tue, 31 Mar 2015 10:45:15 +0200
x86/vdso32/syscall.S: Do not load __USER32_DS to %ss
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> --- arch/x86/vdso/vdso32/syscall.S | 2 -- 1 file changed, 2 deletions(-)
diff --git a/arch/x86/vdso/vdso32/syscall.S b/arch/x86/vdso/vdso32/syscall.S index 5415b56..6b286bb 100644 --- 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:
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