Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754565Ab1BVWeW (ORCPT ); Tue, 22 Feb 2011 17:34:22 -0500 Received: from kroah.org ([198.145.64.141]:46648 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754014Ab1BVWV0 (ORCPT ); Tue, 22 Feb 2011 17:21:26 -0500 X-Mailbox-Line: From gregkh@clark.kroah.org Tue Feb 22 14:18:38 2011 Message-Id: <20110222221838.863586483@clark.kroah.org> User-Agent: quilt/0.48-11.2 Date: Tue, 22 Feb 2011 14:16:57 -0800 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Stefan Bader , Konrad Rzeszutek Wilk Subject: [18/70] xen: p2m: correctly initialize partial p2m leaf In-Reply-To: <20110222222003.GA15831@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3402 Lines: 92 2.6.37-stable review patch. If anyone has any objections, please let us know. ------------------ From: Stefan Bader commit 8e1b4cf2108488ccfb9a3e7ed7cd85a435e01d4b upstream. 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 [v2: Redid a bit of commit wording and fixed a compile warning] Signed-off-by: Stefan Bader Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Greg Kroah-Hartman --- arch/x86/xen/mmu.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) --- a/arch/x86/xen/mmu.c +++ b/arch/x86/xen/mmu.c @@ -395,7 +395,25 @@ void __init xen_build_dynamic_phys_to_ma 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); + 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]; } } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/