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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 675BAC10DCE for ; Fri, 13 Mar 2020 08:27:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 310942073E for ; Fri, 13 Mar 2020 08:27:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726437AbgCMI1D (ORCPT ); Fri, 13 Mar 2020 04:27:03 -0400 Received: from mx2.suse.de ([195.135.220.15]:47248 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726310AbgCMI1C (ORCPT ); Fri, 13 Mar 2020 04:27:02 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 01184B22E; Fri, 13 Mar 2020 08:26:59 +0000 (UTC) Subject: Re: [RFC PATCH 2/2] x86/xen: Make the secondary CPU idle tasks reliable To: Miroslav Benes , boris.ostrovsky@oracle.com, sstabellini@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, jpoimboe@redhat.com Cc: x86@kernel.org, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, jslaby@suse.cz References: <20200312142007.11488-1-mbenes@suse.cz> <20200312142007.11488-3-mbenes@suse.cz> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: <75224ad1-f160-802a-9d72-b092ba864fb7@suse.com> Date: Fri, 13 Mar 2020 09:26:58 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200312142007.11488-3-mbenes@suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On 12.03.20 15:20, Miroslav Benes wrote: > The unwinder reports the secondary CPU idle tasks' stack on XEN PV as > unreliable, which affects at least live patching. > cpu_initialize_context() sets up the context of the CPU through > VCPUOP_initialise hypercall. After it is woken up, the idle task starts > in cpu_bringup_and_idle() function and its stack starts at the offset > right below pt_regs. The unwinder correctly detects the end of stack > there but it is confused by NULL return address in the last frame. > > RFC: I haven't found the way to teach the unwinder about the state of > the stack there. Thus the ugly hack using assembly. Similar to what > startup_xen() has got for boot CPU. > > It introduces objtool "unreachable instruction" warning just right after > the jump to cpu_bringup_and_idle(). It should show the idea what needs > to be done though, I think. Ideas welcome. > > Signed-off-by: Miroslav Benes > --- > arch/x86/xen/smp_pv.c | 3 ++- > arch/x86/xen/xen-head.S | 10 ++++++++++ > 2 files changed, 12 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c > index 802ee5bba66c..6b88cdcbef8f 100644 > --- a/arch/x86/xen/smp_pv.c > +++ b/arch/x86/xen/smp_pv.c > @@ -53,6 +53,7 @@ static DEFINE_PER_CPU(struct xen_common_irq, xen_irq_work) = { .irq = -1 }; > static DEFINE_PER_CPU(struct xen_common_irq, xen_pmu_irq) = { .irq = -1 }; > > static irqreturn_t xen_irq_work_interrupt(int irq, void *dev_id); > +extern unsigned char asm_cpu_bringup_and_idle[]; > > static void cpu_bringup(void) > { Would adding this here work? + asm volatile (UNWIND_HINT(ORC_REG_UNDEFINED, 0, ORC_TYPE_CALL, 1)); Juergen