Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932322AbbFITSO (ORCPT ); Tue, 9 Jun 2015 15:18:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37238 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753122AbbFITSI (ORCPT ); Tue, 9 Jun 2015 15:18:08 -0400 Message-ID: <55773BEC.1060704@redhat.com> Date: Tue, 09 Jun 2015 21:18:04 +0200 From: Denys Vlasenko User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Andy Lutomirski CC: Ingo Molnar , Linus Torvalds , Steven Rostedt , Borislav Petkov , "H. Peter Anvin" , Oleg Nesterov , Frederic Weisbecker , Alexei Starovoitov , Will Drewry , Kees Cook , X86 ML , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 4/5] x86/asm/entry/32: Replace RESTORE_RSI_RDI[_RDX] with open-coded 32-bit reads References: <1433876051-26604-1-git-send-email-dvlasenk@redhat.com> <1433876051-26604-4-git-send-email-dvlasenk@redhat.com> <5577389F.4090301@redhat.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1530 Lines: 34 On 06/09/2015 09:11 PM, Andy Lutomirski wrote: > On Tue, Jun 9, 2015 at 12:03 PM, Denys Vlasenko wrote: >> On 06/09/2015 09:01 PM, Andy Lutomirski wrote: >>> On Tue, Jun 9, 2015 at 11:54 AM, Denys Vlasenko wrote: >>>> This doesn't change much, but this uses shorter 32-bit insns: >>>> >>>> -48 8b 74 24 68 mov 0x68(%rsp),%rsi >>>> -48 8b 7c 24 70 mov 0x70(%rsp),%rdi >>>> -48 8b 54 24 60 mov 0x60(%rsp),%rdx >>>> +8b 74 24 68 mov 0x68(%rsp),%esi >>>> +8b 7c 24 70 mov 0x70(%rsp),%edi >>>> +8b 54 24 60 mov 0x60(%rsp),%edx >>>> >>>> Since these are the only uses of RESTORE_RSI_RDI[_RDX], drop these macros. >>>> >>> >>> It probably doesn't matter for these fast paths, but, for the full >>> slow path return, we really do need to restore the full pt_regs. >>> After all, the syscall we're returning from might be sigreturn. >> >> This is compat 32-bit syscall handling code. >> IIUC we do not restore high half of any registers for 32-bit tasks. >> >> Am I missing something? > > Yes -- 64-bit tasks can call 32-bit compat syscalls. Not via SYSCALL and SYSENTER code paths. This patch touches only those code paths. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/