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Date: Sun, 23 Jan 2011 20:49:18 -0800 From: Jeremy Fitzhardinge <jeremy@...p.org> To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> CC: Stefan Bader <stefan.bader@...onical.com>, Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>, xen-devel@...ts.xensource.com, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [Xen-devel] Re: [PATCH] xen: p2m: correctly initialize partial p2m leave On 01/20/2011 07:10 AM, 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. > Nice catch.. Indeed! >> 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). >> >> Regards, >> Stefan >> >From 1e9c9514caf0399c88ae9288e6db8e3d1c4b4be5 Mon Sep 17 00:00:00 2001 >> From: Stefan Bader <stefan.bader@...onical.com> >> 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: [<c0107397>] 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. Since the p2m page is just a normal page that happens to have been initialized by the domain builder, I think we can just fill the tail of the page with INVALID_P2M_ENTRY in place, rather than having to allocate a new one. J -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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