From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933101AbbLGVwG (ORCPT ); Mon, 7 Dec 2015 16:52:06 -0500 Received: from mail.kernel.org ([198.145.29.136]:47476 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756196AbbLGVv4 (ORCPT ); Mon, 7 Dec 2015 16:51:56 -0500 From: Andy Lutomirski To: x86@kernel.org Cc: linux-kernel@vger.kernel.org, Brian Gerst , Borislav Petkov , =?UTF-8?q?Fr=C3=A9d=C3=A9ric=20Weisbecker?= , Denys Vlasenko , Linus Torvalds , Andy Lutomirski Subject: [PATCH 09/12] x86/entry/64: Stop using int_ret_from_sys_call in ret_from_fork Date: Mon, 7 Dec 2015 13:51:34 -0800 Message-Id: X-Mailer: git-send-email 2.5.0 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ret_from_fork is now open-coded and is no longer tangled up with the syscall code. This isn't so bad -- this adds very little code, and IMO the result is much easier to understand. Signed-off-by: Andy Lutomirski --- arch/x86/entry/entry_64.S | 35 +++++++++++++++++++---------------- 1 file changed, 19 insertions(+), 16 deletions(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 8a6b7ce2beff..81b0944708c5 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -363,7 +363,6 @@ END(stub_ptregs_64) * rdi: prev task we switched from */ ENTRY(ret_from_fork) - LOCK ; btr $TIF_FORK, TI_flags(%r8) pushq $0x0002 @@ -371,28 +370,32 @@ ENTRY(ret_from_fork) call schedule_tail /* rdi: 'prev' task parameter */ - RESTORE_EXTRA_REGS - testb $3, CS(%rsp) /* from kernel_thread? */ + jnz 1f /* - * By the time we get here, we have no idea whether our pt_regs, - * ti flags, and ti status came from the 64-bit SYSCALL fast path, - * the slow path, or one of the 32-bit compat paths. - * Use IRET code path to return, since it can safely handle - * all of the above. + * We came from kernel_thread. This code path is quite twisted, and + * someone should clean it up. + * + * copy_thread_tls stashes the function pointer in RBX and the + * parameter to be passed in RBP. The called function is permitted + * to call do_execve and thereby jump to user mode. */ - jnz int_ret_from_sys_call + movq RBP(%rsp), %rdi + call *RBX(%rsp) + movl $0, RAX(%rsp) /* - * We came from kernel_thread - * nb: we depend on RESTORE_EXTRA_REGS above + * Fall through as though we're exiting a syscall. This makes a + * twisted sort of sense if we just called do_execve. */ - movq %rbp, %rdi - call *%rbx - movl $0, RAX(%rsp) - RESTORE_EXTRA_REGS - jmp int_ret_from_sys_call + +1: + movq %rsp, %rdi + call syscall_return_slowpath /* returns with IRQs disabled */ + TRACE_IRQS_ON /* user mode is traced as IRQS on */ + SWAPGS + jmp restore_regs_and_iret END(ret_from_fork) /* -- 2.5.0