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 2D109C10DCE for ; Fri, 13 Mar 2020 09:54:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 089B62074B for ; Fri, 13 Mar 2020 09:54:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726364AbgCMJyP (ORCPT ); Fri, 13 Mar 2020 05:54:15 -0400 Received: from mx2.suse.de ([195.135.220.15]:40866 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726055AbgCMJyP (ORCPT ); Fri, 13 Mar 2020 05:54:15 -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 6A096ABEA; Fri, 13 Mar 2020 09:54:13 +0000 (UTC) Date: Fri, 13 Mar 2020 10:54:12 +0100 (CET) From: Miroslav Benes To: =?ISO-8859-15?Q?J=FCrgen_Gro=DF?= cc: boris.ostrovsky@oracle.com, sstabellini@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, jpoimboe@redhat.com, x86@kernel.org, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, jslaby@suse.cz Subject: Re: [RFC PATCH 2/2] x86/xen: Make the secondary CPU idle tasks reliable In-Reply-To: <75224ad1-f160-802a-9d72-b092ba864fb7@suse.com> Message-ID: References: <20200312142007.11488-1-mbenes@suse.cz> <20200312142007.11488-3-mbenes@suse.cz> <75224ad1-f160-802a-9d72-b092ba864fb7@suse.com> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="1678380546-951734477-1584093253=:30076" Sender: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --1678380546-951734477-1584093253=:30076 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT On Fri, 13 Mar 2020, Jürgen Groß wrote: > 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)); I tried something similar. It did not work, because than the hint is "bound" to the closest next call in the function which is cr4_init() in this case. The unwinder would not take it into account. In my case, I placed it at the beginning of cpu_bringup_and_idle(). I also open coded it and played with the offset in the orc entry, but that did not work for some other reason. However, now I tried this diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c index 6b88cdcbef8f..39afd88309cb 100644 --- a/arch/x86/xen/smp_pv.c +++ b/arch/x86/xen/smp_pv.c @@ -92,6 +92,7 @@ asmlinkage __visible void cpu_bringup_and_idle(void) { cpu_bringup(); boot_init_stack_canary(); + asm volatile (UNWIND_HINT(ORC_REG_UNDEFINED, 0, ORC_TYPE_CALL, 1)); cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); } and that seems to work. I need to properly verify and test, but the explanation is that as opposed to the above, cpu_startup_entry() is on the idle task's stack and the hint is then taken into account. The unwound stack seems to be complete, so it could indeed be the fix. Thanks Miroslav --1678380546-951734477-1584093253=:30076--