Messages in this thread Patch in this message | | | From | Andy Lutomirski <> | Subject | [GIT PULL 2/4] x86: vdso32/syscall.S: do not load __USER32_DS to %ss | Date | Fri, 27 Mar 2015 11:48:17 -0700 |
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From: Denys Vlasenko <dvlasenk@redhat.com>
This vDSO code only gets used by 64-bit kernel, not 32-bit. In 64-bit kernels, data segment is the same for 32-bit and 64-bit userspace, and SYSRET insn does load %ss with its selector. No need to repeat it by hand. Segment loads are somewhat expensive: tens of cycles.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com> CC: Linus Torvalds <torvalds@linux-foundation.org> CC: Steven Rostedt <rostedt@goodmis.org> CC: Ingo Molnar <mingo@kernel.org> CC: Borislav Petkov <bp@alien8.de> CC: "H. Peter Anvin" <hpa@zytor.com> CC: Andy Lutomirski <luto@amacapital.net> CC: Oleg Nesterov <oleg@redhat.com> CC: Frederic Weisbecker <fweisbec@gmail.com> CC: Alexei Starovoitov <ast@plumgrid.com> CC: Will Drewry <wad@chromium.org> CC: Kees Cook <keescook@chromium.org> CC: x86@kernel.org CC: linux-kernel@vger.kernel.org Message-Id: <1427129240-15543-1-git-send-email-dvlasenk@redhat.com> [removed unnecessary comment] Signed-off-by: Andy Lutomirski <luto@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 5415b5613d55..6b286bb5251c 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: -- 2.3.0
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