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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, 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 41F31C2BB1D for ; Thu, 12 Mar 2020 15:17:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1E64120674 for ; Thu, 12 Mar 2020 15:17:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727743AbgCLPRH (ORCPT ); Thu, 12 Mar 2020 11:17:07 -0400 Received: from mx2.suse.de ([195.135.220.15]:40160 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727455AbgCLPRH (ORCPT ); Thu, 12 Mar 2020 11:17:07 -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 A62CCABF4; Thu, 12 Mar 2020 15:17:05 +0000 (UTC) Date: Thu, 12 Mar 2020 16:17:04 +0100 (CET) From: Miroslav Benes To: Andrew Cooper cc: 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, x86@kernel.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, xen-devel@lists.xenproject.org, jslaby@suse.cz Subject: Re: [Xen-devel] [PATCH 1/2] x86/xen: Make the boot CPU idle task reliable In-Reply-To: Message-ID: References: <20200312142007.11488-1-mbenes@suse.cz> <20200312142007.11488-2-mbenes@suse.cz> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="1678380546-1273645187-1584026225=:28317" 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. --1678380546-1273645187-1584026225=:28317 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT On Thu, 12 Mar 2020, Andrew Cooper wrote: > On 12/03/2020 14:20, Miroslav Benes wrote: > > The unwinder reports the boot CPU idle task's stack on XEN PV as > > unreliable, which affects at least live patching. There are two reasons > > for this. First, the task does not follow the x86 convention that its > > stack starts at the offset right below saved pt_regs. It allows the > > unwinder to easily detect the end of the stack and verify it. Second, > > startup_xen() function does not store the return address before jumping > > to xen_start_kernel() which confuses the unwinder. > > > > Amend both issues by moving the starting point of initial stack in > > startup_xen() and storing the return address before the jump. > > > > Signed-off-by: Miroslav Benes > > --- > > arch/x86/xen/xen-head.S | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S > > index 1d0cee3163e4..642f346bfe02 100644 > > --- a/arch/x86/xen/xen-head.S > > +++ b/arch/x86/xen/xen-head.S > > @@ -35,7 +35,7 @@ SYM_CODE_START(startup_xen) > > rep __ASM_SIZE(stos) > > > > mov %_ASM_SI, xen_start_info > > - mov $init_thread_union+THREAD_SIZE, %_ASM_SP > > + mov $init_thread_union+THREAD_SIZE-SIZEOF_PTREGS, %_ASM_SP > > > > #ifdef CONFIG_X86_64 > > /* Set up %gs. > > @@ -51,7 +51,9 @@ SYM_CODE_START(startup_xen) > > wrmsr > > #endif > > > > + push $1f > > jmp xen_start_kernel > > +1: > > Hang on.  Isn't this just a `call` instruction written in longhand? It is (as far as I know). I wanted to keep it opencoded for a reason I don't remember now. I'll change it. Thanks. Miroslav --1678380546-1273645187-1584026225=:28317--