Re: Xen dom0 crash: "d0:v0: unhandled page fault (ec=0000)"

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Mon, Nov 01, 2010 at 01:39:40PM -0400, Konrad Rzeszutek Wilk wrote:
> > >> http://pastebin.com/3m0DpDdW - 2.6.32.24-gd0054d6-dirty - broken
> .. snip..
> > The way is this is supposed to work is:
> > 
> >    1. Xen gives the domain N pages
> >    2. There's an E820 which describes M pages (M > N)
> >    3. The kernel traverses the existing E820 and finds holes and adds
> >       the memory to a new E820_RAM region beyond M
> >    4. Set up P2M for pages up to N
> >    5. When the kernel maps all "RAM", the region from N-M is not
> >       present, and has no valid P2M mapping; in that case, xen_make_pte
> >       will return a non-present pte.
> 
> Right, and somehow his machine/kernel is not doing this. His 'N' ends up being 'M' so
> the region N-M is added to the "RAM", and xen_make_pte I _think_ returns a non-present pte
> (or maybe it does present a present pte?) In the previous kernel (2.6.32.18), it
> does exactly what you described.

Not that I am actually sure what is causing this. The interesting part is that
he sees this twice:

[    0.000000] last_pfn = 0x2d0699 max_arch_pfn = 0x400000000
[    0.000000] last_pfn = 0x2f000 max_arch_pfn = 0x400000000

And he mentioned on IRC to me that this was not due to any debugging patches.