Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932746AbbFIT12 (ORCPT ); Tue, 9 Jun 2015 15:27:28 -0400 Received: from mail-lb0-f172.google.com ([209.85.217.172]:36079 "EHLO mail-lb0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932530AbbFIT1W (ORCPT ); Tue, 9 Jun 2015 15:27:22 -0400 MIME-Version: 1.0 In-Reply-To: <55773BEC.1060704@redhat.com> References: <1433876051-26604-1-git-send-email-dvlasenk@redhat.com> <1433876051-26604-4-git-send-email-dvlasenk@redhat.com> <5577389F.4090301@redhat.com> <55773BEC.1060704@redhat.com> From: Andy Lutomirski Date: Tue, 9 Jun 2015 12:27:00 -0700 Message-ID: Subject: Re: [PATCH 4/5] x86/asm/entry/32: Replace RESTORE_RSI_RDI[_RDX] with open-coded 32-bit reads To: Denys Vlasenko 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" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1861 Lines: 42 On Tue, Jun 9, 2015 at 12:18 PM, Denys Vlasenko wrote: > 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. I suppose that's true enough even if it's not quite true. A 64-bit task could far jump/call/return to compat mode and then do SYSCALL or SYSENTER, but it will likely crash and burn because there's no 32-bit vdso. --Andy -- 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/