From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755991AbbGCQYn (ORCPT ); Fri, 3 Jul 2015 12:24:43 -0400 Received: from mail-la0-f54.google.com ([209.85.215.54]:36000 "EHLO mail-la0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755843AbbGCQYe (ORCPT ); Fri, 3 Jul 2015 12:24:34 -0400 MIME-Version: 1.0 In-Reply-To: References: <1a5858d079609a3e293123c9ee45de433a4e9c44.1435602481.git.luto@kernel.org> <20150702120932.GH4001@pd.tnic> From: Andy Lutomirski Date: Fri, 3 Jul 2015 09:24:14 -0700 Message-ID: Subject: Re: [PATCH v4 14/17] x86/asm/entry/64: Migrate error and interrupt exit work to C To: Denys Vlasenko Cc: Borislav Petkov , Andy Lutomirski , X86 ML , "linux-kernel@vger.kernel.org" , =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVja2Vy?= , Rik van Riel , Oleg Nesterov , Kees Cook , Brian Gerst , Paul McKenney Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 3, 2015 at 7:37 AM, Denys Vlasenko wrote: > On Thu, Jul 2, 2015 at 6:09 PM, Andy Lutomirski wrote: >> On Thu, Jul 2, 2015 at 5:09 AM, Borislav Petkov wrote: >>> On Mon, Jun 29, 2015 at 12:33:46PM -0700, Andy Lutomirski wrote: >>>> Signed-off-by: Andy Lutomirski >>>> --- >>>> arch/x86/entry/entry_64.S | 63 +++++++++++----------------------------- >>>> arch/x86/entry/entry_64_compat.S | 5 ++++ >>>> 2 files changed, 22 insertions(+), 46 deletions(-) >>>> >>>> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S >>>> index ce2c9049abef..08a37ec049f0 100644 >>>> --- a/arch/x86/entry/entry_64.S >>>> +++ b/arch/x86/entry/entry_64.S >>>> @@ -508,7 +508,16 @@ END(irq_entries_start) >>>> >>>> testb $3, CS(%rsp) >>>> jz 1f >>>> + >>>> + /* >>>> + * IRQ from user mode. Switch to kernel gsbase and inform context >>>> + * tracking that we're in kernel mode. >>>> + */ >>>> SWAPGS >>>> +#ifdef CONFIG_CONTEXT_TRACKING >>>> + call enter_from_user_mode >>>> +#endif >>> >>> I think you can make this much cleaner by getting rid of the ifdeffery >>> and pushing it into the enter_from_user_mode() function: >>> >>> __visible void enter_from_user_mode(void) >>> { >>> #ifdef CONFIG_CONTEXT_TRACKING >>> >>> ... >>> >>> #endif >>> } >>> >>> The disadvantage of all that cleanliness is that we get one dumb >>> >>> call enter_from_user_mode >>> >>> there to this abomination: >>> >>> ffffffff810014f0 : >>> ffffffff810014f0: e8 db 97 67 00 callq ffffffff8167acd0 <__fentry__> >>> ffffffff810014f5: 55 push %rbp >>> ffffffff810014f6: 48 89 e5 mov %rsp,%rbp >>> ffffffff810014f9: 5d pop %rbp >>> ffffffff810014fa: c3 retq >>> ffffffff810014fb: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1) >>> >>> which sux. >>> >>> We sure could use LTO here. >>> >> >> You mean link-time asm optimizations? Turning off frame pointers in >> leaf functions as long as rbp is still preserved might not be so >> terrible either. >> >> I'm torn on this one. In principle, you're right, or we could have a >> macro CALL_ENTER_FROM_USER_MODE that does nothing if context tracking >> is off. OTOH, that's also kind of messy. > > busybox has IF() macros: > > IF_CONTEXT_TRACKING(call enter_from_user_mode) > > Unlike #if, this needs one line, not three. I predict all of these call sites will get moved to C before 4.3. If not, then I'd be glad to clean this part up. --Andy