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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,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 8128CC432C1 for ; Wed, 25 Sep 2019 11:01:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 54DAA21D7A for ; Wed, 25 Sep 2019 11:01:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2403947AbfIYLB4 (ORCPT ); Wed, 25 Sep 2019 07:01:56 -0400 Received: from know-smtprelay-omc-7.server.virginmedia.net ([80.0.253.71]:46121 "EHLO know-smtprelay-omc-7.server.virginmedia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2403867AbfIYLB4 (ORCPT ); Wed, 25 Sep 2019 07:01:56 -0400 Received: from mail0.xen.dingwall.me.uk ([82.47.84.47]) by cmsmtp with ESMTPA id D53Qi4CI0wGUPD53Ri497I; Wed, 25 Sep 2019 12:01:53 +0100 X-Originating-IP: [82.47.84.47] X-Authenticated-User: james.dingwall@blueyonder.co.uk X-Spam: 0 X-Authority: v=2.3 cv=Kc78TzQD c=1 sm=1 tr=0 a=0bfgdX8EJi0Cr9X0x0jFDA==:117 a=0bfgdX8EJi0Cr9X0x0jFDA==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=8nJEP1OIZ-IA:10 a=xqWC_Br6kY4A:10 a=J70Eh1EUuV4A:10 a=R3OVokhvzph9xWr5bnAA:9 a=wPNLvfGTeEIA:10 Received: from localhost (localhost [IPv6:::1]) by mail0.xen.dingwall.me.uk (Postfix) with ESMTP id A659E10D2A7; Wed, 25 Sep 2019 11:01:52 +0000 (UTC) X-Virus-Scanned: Debian amavisd-new at dingwall.me.uk Received: from mail0.xen.dingwall.me.uk ([127.0.0.1]) by localhost (mail0.xen.dingwall.me.uk [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id USOBNqyBtDPy; Wed, 25 Sep 2019 11:01:52 +0000 (UTC) Received: from behemoth.dingwall.me.uk (behemoth.dingwall.me.uk [IPv6:2001:470:695c:302::c0a8:105]) by dingwall.me.uk (Postfix) with ESMTP id 6F60310D2A4; Wed, 25 Sep 2019 11:01:52 +0000 (UTC) Received: by behemoth.dingwall.me.uk (Postfix, from userid 1000) id 58172FB608; Wed, 25 Sep 2019 11:01:52 +0000 (UTC) Date: Wed, 25 Sep 2019 11:01:52 +0000 From: James Dingwall To: Boris Ostrovsky , Kees Cook , "linux-kernel@vger.kernel.org" Cc: Anton Vorontsov , Colin Cross , Juergen Gross , "Luck, Tony" , Matthias Kaehlcke , Greg Kroah-Hartman Subject: Re: pstore does not work under xen Message-ID: <20190925110152.GA31550@dingwall.me.uk> References: <20190919102643.GA9400@dingwall.me.uk> <3908561D78D1C84285E8C5FCA982C28F7F472015@ORSMSX115.amr.corp.intel.com> <20190919161430.GA28042@dingwall.me.uk> <20190923154227.GA11201@dingwall.me.uk> <201909231556.7FF7A11@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-CMAE-Envelope: MS4wfEO2FbJeaZSLiyToWx2IURbsIZpX9oT4HCG7RhrySskcO2p7R96PcRT6u+eIV3FMxxEWqqPtNx6CwZ7hQbtSrL9cBDZo6mLOVXzNxATMvnfG8od5gNaY mnz48ivj1uwlgcAhOuwm5haHBBAjrT/Xcc3dW/2MOduYovyouZ4IFdhDvE5J/ksxDGaVSy291fCH2JJrC5qlNz3dz9NEcnmWorPMbYBLhV5nvGqg6V4fTG5+ iBa7rHNwFg42r3tZPs+tJxanGh9HiwKZUQSbcCqye7hHpscQ0cnFWZeSQ4FSZoIE8o4dNY+QA7B02ZZ8AHY/IzkSiUhlRQXNvGSfd6ww8mjCAFbawwM8nikf WgkeeNNECKL/hJcj84ldH3TnCh0QQM1Yrj7xgjpd2B9tZWYn9CpRDDAZuZxSElETBghaiQoOLF8VDvl0gffcNEAPOYMO6w== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 23, 2019 at 08:41:05PM -0400, Boris Ostrovsky wrote: > On 9/23/19 6:59 PM, Kees Cook wrote: > > On Mon, Sep 23, 2019 at 03:42:27PM +0000, James Dingwall wrote: > >> On Thu, Sep 19, 2019 at 12:37:40PM -0400, Boris Ostrovsky wrote: > >>> On 9/19/19 12:14 PM, James Dingwall wrote: > >>>> On Thu, Sep 19, 2019 at 03:51:33PM +0000, Luck, Tony wrote: > >>>>>> I have been investigating a regression in our environment where pstore > >>>>>> (efi-pstore specifically but I suspect this would affect all > >>>>>> implementations) no longer works after upgrading from a 4.4 to 5.0 > >>>>>> kernel when running under xen. (This is an Ubuntu kernel but I don't > >>>>>> think there are patches which affect this area.) > >>>>> I don't have any answer for this ... but want to throw out the idea that > >>>>> VMM systems could provide some hypercalls to guests to save/return > >>>>> some blob of memory (perhaps the "save" triggers automagically if the > >>>>> guest crashes?). > >>>>> > >>>>> That would provide a much better pstore back end than relying on emulation > >>>>> of EFI persistent variables (which have severe contraints on size, and don't > >>>>> support some pstore modes because you can't dynamically update EFI variables > >>>>> hundreds of times per second). > >>>>> > >>>> For clarification this is a dom0 crash rather than an HVM guest with EFI. I > >>>> should probably have also mentioned the xen verion has changed from 4.8.4 to > >>>> 4.11.2 in case its behaviour on detection of crashed domain has changed. > >>>> > >>>> (For capturing guest crashes we have enabled xenconsole logging so the > >>>> hvc0 log is available in dom0.) > >>> > >>> Do you only see this difference between 4.4 and 5.0 when you crash via > >>> sysrq? > >>> > >>> Because that's where things changed. On 4.4 we seem to be forcing an > >>> oops, which eventually calls kmsg_dump() and then panic. On 5.0 we call > >>> panic() directly from sysrq handler. And because Xen's panic notifier > >>> doesn't return we never get a chance to call kmsg_dump(). > >>> > >> Ok, I see that change in 8341f2f222d729688014ce8306727fdb9798d37e. I > >> hadn't tested it any other way before. Using the null pointer > >> de-reference module code at [1] a pstore record is generated as expected > >> when the module is loaded (panic_on_oops=1). > > This change looks correct -- it just gets us directly to the panic() > > state instead of exercising the various exception handlers. > > > >> I have also tested swapping the kmsg_dump() / > >> atomic_notifier_call_chain() around in panic.c and this also results in > >> a pstore record being created with sysrq-c. I don't know if that would > >> be an acceptable solution though since it may break behaviour that other > >> things depend on. > > I don't think reordering these is a good idea: as the comments say, > > there might be work done in the notifier chain that kmsg_dump() will > > want to capture (e.g. the KASLR base offset). > > > > The situation seems to be that notifier callbacks must return -- I think > > Xen needs fixing here. > > > > I only had one quick sanity test with a PV guest so this needs more > testing. James, can you give it a try? I have tested the patch in a pv domU and in dom0. The kernel was built with a default Ubuntu .config which sets CONFIG_PANIC_TIMEOUT=0. uname -r = 5.0.0-27-generic. In the domU (no custom kernel parameters): - sysrq-c: I saw my debug printk messages about kmsg_dump() being invoked after the traceback and the domain became listed as crashed in the xl status output. - halt -p: clean shutdown - shutdown -r now: clean reboot In the domU with panic=15 in kernel parameters: - sysrq-c: as without panic=15 then final message "Rebooting in 15 seconds.." printed but domain never rebooted. Without this patch the domain doesn't reboot or print the Rebooting message presumably because of the non-returning panic handler. If that message is reached then I think I would expect a reboot. (In our Linux 4.4 / Xen 4.8.4 environment no value of panic resulted in reboot.) - halt -p: clean shutdown - shutdown -r now: clean reboot In dom0 with oops=panic panic=15 in the kernel parameters: - sysrq-c: kmsg_dump() debug messages printed, last linux message "Rebooting in 15 seconds..", after 15s "(XEN) Hardware Dom0 crashed: rebooting machine in 5 seconds.", after 5s system rebooted. On the next start a pstore record is present as expected. - halt -p: clean shutdown, no pstore record present on next start. - shutdown -r now: clean reboot, no pstore record present on next start. In dom0 with panic=0: - sysrq-c: dom0 crashes, no reboot messages printed from Xen or kernel and system hangs. A pstore record is present on next start. - halt -p: clean shutdown, no pstore record present on next start. - shutdown -r now: clean reboot, no pstore record present on next start. In my opinion this patch: - fixes the original issue of no pstore record being generated for a dom0 panic. - respects the dom0 panic=... value. This is a change in behaviour in how xen handles the crashed dom0 from always rebooting to only rebooting if panic > 0. - causes a Rebooting message to be printed in a crashed pv domU when panic > 0 but the domain does not reboot when it should. James > > > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c > index 750f46ad018a..d88f118028b4 100644 > --- a/arch/x86/xen/enlighten.c > +++ b/arch/x86/xen/enlighten.c > @@ -269,16 +269,17 @@ void xen_reboot(int reason) >                 BUG(); >  } >   > +static int reboot_reason = SHUTDOWN_reboot; >  void xen_emergency_restart(void) >  { > -       xen_reboot(SHUTDOWN_reboot); > +       xen_reboot(reboot_reason); >  } >   >  static int >  xen_panic_event(struct notifier_block *this, unsigned long event, void > *ptr) >  { >         if (!kexec_crash_loaded()) > -               xen_reboot(SHUTDOWN_crash); > +               reboot_reason = SHUTDOWN_crash; >         return NOTIFY_DONE; >  } >   > @@ -290,6 +291,8 @@ static struct notifier_block xen_panic_block = { >  int xen_panic_handler_init(void) >  { >         atomic_notifier_chain_register(&panic_notifier_list, > &xen_panic_block); > +       if (panic_timeout == 0) > +               set_arch_panic_timeout(-1, CONFIG_PANIC_TIMEOUT); >         return 0; >  } > >