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 E2BBAC4332B for ; Thu, 19 Mar 2020 10:31:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C0ACF20722 for ; Thu, 19 Mar 2020 10:31:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727083AbgCSKbV (ORCPT ); Thu, 19 Mar 2020 06:31:21 -0400 Received: from mx2.suse.de ([195.135.220.15]:56756 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726589AbgCSKbV (ORCPT ); Thu, 19 Mar 2020 06:31:21 -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 44D14B197; Thu, 19 Mar 2020 10:31:19 +0000 (UTC) Date: Thu, 19 Mar 2020 11:31:18 +0100 (CET) From: Miroslav Benes To: Jan Beulich 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, andrew.cooper3@citrix.com, x86@kernel.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, xen-devel@lists.xenproject.org, jslaby@suse.cz Subject: Re: [PATCH v2 1/2] x86/xen: Make the boot CPU idle task reliable In-Reply-To: <71c4eeaf-958a-b215-3033-c3e0d74a9cfa@suse.com> Message-ID: References: <20200319095606.23627-1-mbenes@suse.cz> <20200319095606.23627-2-mbenes@suse.cz> <71c4eeaf-958a-b215-3033-c3e0d74a9cfa@suse.com> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Thu, 19 Mar 2020, Jan Beulich wrote: > On 19.03.2020 10:56, 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, which is > > exactly what call instruction does. > > > > Signed-off-by: Miroslav Benes > > --- > > arch/x86/xen/xen-head.S | 8 ++++++-- > > 1 file changed, 6 insertions(+), 2 deletions(-) > > > > diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S > > index 1d0cee3163e4..edc776af0e0a 100644 > > --- a/arch/x86/xen/xen-head.S > > +++ b/arch/x86/xen/xen-head.S > > @@ -35,7 +35,11 @@ SYM_CODE_START(startup_xen) > > rep __ASM_SIZE(stos) > > > > mov %_ASM_SI, xen_start_info > > - mov $init_thread_union+THREAD_SIZE, %_ASM_SP > > +#ifdef CONFIG_X86_64 > > + mov initial_stack(%rip), %_ASM_SP > > +#else > > + mov pa(initial_stack), %_ASM_SP > > +#endif > > If you need to distinguish the two anyway, why not use %rsp and > %esp respectively? I could, I just preferred the unification instead. Will change it if you think it would be better. Miroslav