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=-6.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,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 72289C43441 for ; Mon, 26 Nov 2018 17:10:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 442FB20663 for ; Mon, 26 Nov 2018 17:10:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 442FB20663 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727162AbeK0EFZ (ORCPT ); Mon, 26 Nov 2018 23:05:25 -0500 Received: from mx1.redhat.com ([209.132.183.28]:55724 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726224AbeK0EFZ (ORCPT ); Mon, 26 Nov 2018 23:05:25 -0500 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 E62B812E518; Mon, 26 Nov 2018 17:10:41 +0000 (UTC) Received: from treble (ovpn-121-105.rdu2.redhat.com [10.10.121.105]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0741E1057075; Mon, 26 Nov 2018 17:10:38 +0000 (UTC) Date: Mon, 26 Nov 2018 11:10:36 -0600 From: Josh Poimboeuf To: Peter Zijlstra Cc: x86@kernel.org, linux-kernel@vger.kernel.org, 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" Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64 Message-ID: <20181126171036.chcbmb35ygpxziub@treble> References: <62188c62f6dda49ca2e20629ee8e5a62a6c0b500.1543200841.git.jpoimboe@redhat.com> <20181126160217.GR2113@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181126160217.GR2113@hirez.programming.kicks-ass.net> 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 [10.5.110.38]); Mon, 26 Nov 2018 17:10:42 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 26, 2018 at 05:02:17PM +0100, Peter Zijlstra wrote: > On Mon, Nov 26, 2018 at 07:55:00AM -0600, Josh Poimboeuf wrote: > > diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c > > index 8026d176f25c..d3869295b88d 100644 > > --- a/arch/x86/kernel/static_call.c > > +++ b/arch/x86/kernel/static_call.c > > @@ -9,13 +9,21 @@ > > > > void static_call_bp_handler(void); > > void *bp_handler_dest; > > +void *bp_handler_continue; > > > > asm(".pushsection .text, \"ax\" \n" > > ".globl static_call_bp_handler \n" > > ".type static_call_bp_handler, @function \n" > > "static_call_bp_handler: \n" > > - "ANNOTATE_RETPOLINE_SAFE \n" > > +#ifdef CONFIG_HAVE_STATIC_CALL_INLINE > > + ANNOTATE_RETPOLINE_SAFE > > + "call *bp_handler_dest \n" > > + ANNOTATE_RETPOLINE_SAFE > > + "jmp *bp_handler_continue \n" > > +#else /* !CONFIG_HAVE_STATIC_CALL_INLINE */ > > + ANNOTATE_RETPOLINE_SAFE > > "jmp *bp_handler_dest \n" > > +#endif > > ".popsection \n"); > > > > void arch_static_call_transform(void *site, void *tramp, void *func) > > @@ -25,7 +33,10 @@ void arch_static_call_transform(void *site, void *tramp, void *func) > > unsigned char insn_opcode; > > unsigned char opcodes[CALL_INSN_SIZE]; > > > > - insn = (unsigned long)tramp; > > + if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE)) > > + insn = (unsigned long)site; > > + else > > + insn = (unsigned long)tramp; > > > > mutex_lock(&text_mutex); > > > > @@ -41,8 +52,10 @@ void arch_static_call_transform(void *site, void *tramp, void *func) > > opcodes[0] = insn_opcode; > > memcpy(&opcodes[1], &dest_relative, CALL_INSN_SIZE - 1); > > > > - /* Set up the variable for the breakpoint handler: */ > > + /* Set up the variables for the breakpoint handler: */ > > bp_handler_dest = func; > > + if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE)) > > + bp_handler_continue = (void *)(insn + CALL_INSN_SIZE); > > > > /* Patch the call site: */ > > text_poke_bp((void *)insn, opcodes, CALL_INSN_SIZE, > > OK, so this is where that static_call_bp_handler comes from; you need > that CALL to frob the stack. > > But I still think it is broken; consider: > > CPU0 CPU1 > > bp_handler = ponies; > > text_poke_bp(, &static_call_bp_handler) > text_poke(&int3); > on_each_cpu(sync) > > ... > > > text_poke(/* all but first bytes */) > on_each_cpu(sync) > > ... > > > > pt_regs->ip = &static_call_bp_handler > > > // VCPU takes a nap... > text_poke(/* first byte */) > on_each_cpu(sync) > > ... > > > // VCPU sleeps more > bp_handler = unicorn; > > CALL unicorn > > *whoops* > > Now, granted, that is all rather 'unlikely', but that never stopped > Murphy. Good find, thanks Peter. As we discussed on IRC, we'll need to fix this from within the int3 exception handler by faking the call: putting a fake return address on the stack (pointing to right after the call) and setting regs->ip to the called function. And for the out-of-line case we can just jump straight to the function, so the function itself will be the text_poke_bp() "handler". So the static_call_bp_handler() trampoline will go away. -- Josh