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

[Gianni Tedesco <gianni.tedesco@xxxxxxxxxx>]

On Mon, 2010-11-01 at 18:16 +0000, Jeremy Fitzhardinge wrote:
> On 11/01/2010 01:46 PM, Konrad Rzeszutek Wilk wrote:
> > 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.
> 
> That's just printed by e820_end_pfn(), which is called a few times. 
> Does it happen native?

It's just called twice once for max mem and once for max_low_mem which
are different for me (ie. correspond to N and M respectively).

Not sure if it happens on bare metal

Gianni


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