Re: pvgrub "Error 9: Unknown boot failure" booting Debian Jessie kernel (Was: Re: [PATCH v5 6/9] libxc: create unmapped initrd in domain builder if supported)

[Juergen Gross <jgross@suse.com>]

On 01/12/15 09:30, Ian Campbell wrote:
> On Tue, 2015-12-01 at 08:41 +0100, Juergen Gross wrote:
>>>> I'm not quite sure what to make of this, in particular I don't see
>> anything
>>>> in kexec.c which obviously looks after unmapping the heap or brk
>> areas.
>>>
>>> Nah, this backtrace shows a normal allocation path while
>>> uncompressing the kernel image. I'd expect something like that.
>>> Why shouldn't mini-os make use of pfn 4d81 somewhere?
> 
> That pfn ends up right in the middle of the next-kernels vaddr mapping,
> so at best it indicates some sort of disconnect/overlap between the
> mini-os memory allocator and the domain-builder memory allocator.

I don't think so.

mini-os just allocates single pages and keeps the relation to the
(future) pfn of that page. The p2m list is adjusted later to move the
allocated page to that pfn before activating the new kernel.

> Since it seems to be in the middle of the padding area (which might
> have been new in ea7c8a3d0e82, I'm not sure, it seems to be more
> explicit at the least) it occurred to me on the way home last night
> that maybe we need to unmap the padding area as well.

We do. The page tables need to be unmapped independently as they
have been mapped explicitly during setup_pgtables(dom). All the
mini-os mappings are removed in a loop just after that.

> I'll try that and your suggested patch below as well once I get to the
> office this morning.

Thanks.


Juergen