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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT 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 0265AC1975A for ; Thu, 12 Mar 2020 14:20:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D99B320650 for ; Thu, 12 Mar 2020 14:20:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727555AbgCLOUN (ORCPT ); Thu, 12 Mar 2020 10:20:13 -0400 Received: from mx2.suse.de ([195.135.220.15]:58400 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727390AbgCLOUM (ORCPT ); Thu, 12 Mar 2020 10:20:12 -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 CD2FCB2FA; Thu, 12 Mar 2020 14:20:10 +0000 (UTC) From: Miroslav Benes To: boris.ostrovsky@oracle.com, jgross@suse.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, Miroslav Benes Subject: [RFC PATCH 2/2] x86/xen: Make the secondary CPU idle tasks reliable Date: Thu, 12 Mar 2020 15:20:07 +0100 Message-Id: <20200312142007.11488-3-mbenes@suse.cz> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200312142007.11488-1-mbenes@suse.cz> References: <20200312142007.11488-1-mbenes@suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org 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) { @@ -309,7 +310,7 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle) * pointing just below where pt_regs would be if it were a normal * kernel entry. */ - ctxt->user_regs.eip = (unsigned long)cpu_bringup_and_idle; + ctxt->user_regs.eip = (unsigned long)asm_cpu_bringup_and_idle; ctxt->flags = VGCF_IN_KERNEL; ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */ ctxt->user_regs.ds = __USER_DS; diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S index 642f346bfe02..c9a9c0bb79ed 100644 --- a/arch/x86/xen/xen-head.S +++ b/arch/x86/xen/xen-head.S @@ -56,6 +56,16 @@ SYM_CODE_START(startup_xen) 1: SYM_CODE_END(startup_xen) __FINIT + +.pushsection .text +SYM_CODE_START(asm_cpu_bringup_and_idle) + UNWIND_HINT_EMPTY + + push $1f + jmp cpu_bringup_and_idle +1: +SYM_CODE_END(asm_cpu_bringup_and_idle) +.popsection #endif .pushsection .text -- 2.25.1