From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753649Ab1AUOnK (ORCPT ); Fri, 21 Jan 2011 09:43:10 -0500 Received: from adelie.canonical.com ([91.189.90.139]:46894 "EHLO adelie.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753249Ab1AUOnE (ORCPT ); Fri, 21 Jan 2011 09:43:04 -0500 Message-ID: <4D399B72.3000103@canonical.com> Date: Fri, 21 Jan 2011 15:42:58 +0100 From: Stefan Bader User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.13) Gecko/20101208 Lightning/1.0b2 Thunderbird/3.1.7 MIME-Version: 1.0 To: Konrad Rzeszutek Wilk CC: Jeremy Fitzhardinge , xen-devel@lists.xensource.com, Linux Kernel Mailing List Subject: Re: [Xen-devel] [PATCH] xen: p2m: correctly initialize partial p2m leave References: <4D3848DF.9000906@canonical.com> <20110121142647.GA27319@dumpdata.com> In-Reply-To: <20110121142647.GA27319@dumpdata.com> X-Enigmail-Version: 1.1.2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/21/2011 03:26 PM, Konrad Rzeszutek Wilk wrote: > On Thu, Jan 20, 2011 at 03:38:23PM +0100, Stefan Bader wrote: >> There have been changes and code been moved around, so this is just a quick >> rebase of the change I tested on a 2.6.37 based kernel. The basic problem seem >> still valid, though. > > Yup. >> >> Initially I thought of adding a cc to stable into the s-o-b, but the patch needs >> to be adapted anyway (I can supply that version if the way I fixed the issue >> looks ok). > > OK, let me send this upstream to Linus for adaption. I fixed one compile warning > but otherwsie it is the same. Look below for details. > > And when that is done I would appreciate you sending a copy to stable. > Sure, will do that as soon as the change hits 2.6.38 upstream. -Stefan >> >> Regards, >> Stefan > >> >From 1e9c9514caf0399c88ae9288e6db8e3d1c4b4be5 Mon Sep 17 00:00:00 2001 >> From: Stefan Bader >> Date: Thu, 20 Jan 2011 11:37:43 +0100 >> Subject: [PATCH] xen: p2m: correctly initialize partial p2m leave >> >> After changing the p2m mapping to a tree by >> >> commit 58e05027b530ff081ecea68e38de8d59db8f87e0 >> xen: convert p2m to a 3 level tree >> >> and trying to boot a DomU with 615MB of memory, the following crash was >> observed in the dump: >> >> kernel direct mapping tables up to 26f00000 @ 1ec4000-1fff000 >> BUG: unable to handle kernel NULL pointer dereference at (null) >> IP: [] xen_set_pte+0x27/0x60 >> *pdpt = 0000000000000000 *pde = 0000000000000000 >> >> Adding further debug statements showed that when trying to set up >> pfn=0x26700 the returned mapping was invalid. >> >> pfn=0x266ff calling set_pte(0xc1fe77f8, 0x6b3003) >> pfn=0x26700 calling set_pte(0xc1fe7800, 0x3) >> >> Although the last_pfn obtained from the startup info is 0x26700, which >> should in turn not be hit, the additional 8MB which are added as extra >> memory normally seem to be ok. This lead to looking into the initial >> p2m tree construction, which uses the smaller value and assuming that >> there is other code handling the extra memory. >> >> When the p2m tree is set up, the leaves are directly pointed to the >> array which the domain builder set up. But if the mapping is not on a >> boundary that fits into one p2m page, this will result in the last leaf >> being only partially valid. And as the invalid entries are not >> initialized in that case, things go badly wrong. >> >> I am trying to fix that by checking whether the current leaf is a >> complete map and if not, allocate a completely new page and copy only >> the valid pointers there. This may not be the most efficient or elegant >> solution, but at least it seems to allow me booting DomUs with memory >> assignments all over the range. >> >> BugLink: http://bugs.launchpad.net/bugs/686692 >> >> Signed-off-by: Stefan Bader >> --- >> arch/x86/xen/p2m.c | 20 +++++++++++++++++++- >> 1 files changed, 19 insertions(+), 1 deletions(-) >> >> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c >> index 8f2251d..c9307ec 100644 >> --- a/arch/x86/xen/p2m.c >> +++ b/arch/x86/xen/p2m.c >> @@ -237,7 +237,25 @@ void __init xen_build_dynamic_phys_to_machine(void) >> p2m_top[topidx] = mid; >> } >> >> - p2m_top[topidx][mididx] = &mfn_list[pfn]; >> + /* >> + * As long as the mfn_list has enough entries to completely >> + * fill a p2m page, pointing into the array is ok. But if >> + * not the entries beyond the last pfn will be undefined. >> + * And guessing that the 'what-ever-there-is' does not take it >> + * too kindly when changing it to invalid markers, a new page >> + * is allocated, initialized and filled with the valid part. >> + */ >> + if (unlikely(pfn + P2M_PER_PAGE > max_pfn)) { >> + unsigned long p2midx; >> + unsigned long **p2m = extend_brk(PAGE_SIZE, PAGE_SIZE); > > unsigned long *p2m. > > >> + p2m_init(p2m); >> + >> + for (p2midx = 0; pfn + p2midx < max_pfn; p2midx++) { >> + p2m[p2midx] = mfn_list[pfn + p2midx]; >> + } >> + p2m_top[topidx][mididx] = p2m; >> + } else >> + p2m_top[topidx][mididx] = &mfn_list[pfn]; >> } >> >> m2p_override_init(); >> -- >> 1.7.0.4 >> > >> _______________________________________________ >> Xen-devel mailing list >> Xen-devel@lists.xensource.com >> http://lists.xensource.com/xen-devel >