From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9F622C4321A for ; Mon, 10 Jun 2019 18:55:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 83C70207E0 for ; Mon, 10 Jun 2019 18:55:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389043AbfFJSz2 (ORCPT ); Mon, 10 Jun 2019 14:55:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54780 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388069AbfFJSz2 (ORCPT ); Mon, 10 Jun 2019 14:55:28 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2DEBC5AFD9; Mon, 10 Jun 2019 18:55:24 +0000 (UTC) Received: from treble (ovpn-121-189.rdu2.redhat.com [10.10.121.189]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 03B1E1001DC0; Mon, 10 Jun 2019 18:55:14 +0000 (UTC) Date: Mon, 10 Jun 2019 13:55:13 -0500 From: Josh Poimboeuf To: Nadav Amit Cc: Peter Zijlstra , the arch/x86 maintainers , LKML , Ard Biesheuvel , Andy Lutomirski , Steven Rostedt , Ingo Molnar , Thomas Gleixner , Linus Torvalds , Masami Hiramatsu , Jason Baron , Jiri Kosina , David Laight , Borislav Petkov , Julia Cartwright , Jessica Yu , "H. Peter Anvin" , Rasmus Villemoes , Edward Cree , Daniel Bristot de Oliveira Subject: Re: [PATCH 13/15] x86/static_call: Add inline static call implementation for x86-64 Message-ID: <20190610185513.pbtc7udpkfd5jsuu@treble> References: <20190605130753.327195108@infradead.org> <20190605131945.313688119@infradead.org> <20190610183357.zj6rwdpgw36anpfc@treble> <40096B8A-C063-4219-89FC-A8E42981BF28@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <40096B8A-C063-4219-89FC-A8E42981BF28@vmware.com> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Mon, 10 Jun 2019 18:55:27 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 10, 2019 at 06:45:52PM +0000, Nadav Amit wrote: > > On Jun 10, 2019, at 11:33 AM, Josh Poimboeuf wrote: > > > > On Wed, Jun 05, 2019 at 03:08:06PM +0200, Peter Zijlstra wrote: > >> --- a/arch/x86/include/asm/static_call.h > >> +++ b/arch/x86/include/asm/static_call.h > >> @@ -2,6 +2,20 @@ > >> #ifndef _ASM_STATIC_CALL_H > >> #define _ASM_STATIC_CALL_H > >> > >> +#include > >> + > >> +#ifdef CONFIG_HAVE_STATIC_CALL_INLINE > >> + > >> +/* > >> + * This trampoline is only used during boot / module init, so it's safe to use > >> + * the indirect branch without a retpoline. > >> + */ > >> +#define __ARCH_STATIC_CALL_TRAMP_JMP(key, func) \ > >> + ANNOTATE_RETPOLINE_SAFE \ > >> + "jmpq *" __stringify(key) "+" __stringify(SC_KEY_func) "(%rip) \n" > >> + > >> +#else /* !CONFIG_HAVE_STATIC_CALL_INLINE */ > > > > I wonder if we can simplify this (and drop the indirect branch) by > > getting rid of the above cruft, and instead just use the out-of-line > > trampoline as the default for inline as well. > > > > Then the inline case could fall back to the out-of-line implementation > > (by patching the trampoline's jmp dest) before static_call_initialized > > is set. > > I must be missing some context - but what guarantees that this indirect > branch would be exactly 5 bytes long? Isn’t there an assumption that this > would be the case? Shouldn’t there be some handling of the padding? We don't patch the indirect branch. It's just part of a temporary trampoline which is called by the call site, and which does "jmp key->func" during boot until static call initialization is done. (Though I'm suggesting removing that.) -- Josh