Re: [Xen-devel] BUG: xend oopses on munmap of /proc/xen/privcmd

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 25 Apr 2005, at 23:29, Rik van Riel wrote:

> This is with last night's Xen snapshot (apr 24th), on kernel
> 2.6.12-rc3 - but the mess is so horrid that I'm not quite sure
> how to fix it...
>
> This oops prevents xen from starting xenU domains.
>
> Basically xend does the following:
> 1) mmap /proc/xen/privcmd
> 2) call an ioctl to populate the mmap
> 3) munmap the mapping created in (1)
Various people have been seeing this, although I haven't reproduced it 
on my own test box. The problem is not the munmap itself (although it 
obviously needs robustifying) but that something (presumably the ioctl) 
has mmaped bogus pages. The ioctl is only supposed to mmap the new 
domain's pages -- these will have pfn_valid() as false and so will not 
take the set_page_dirty() path in zap_pte_range.
It sounds to be related to my patch from Friday that removed redundant 
dom0_ops and changed xc_domain_create() to also call DOM0_SETMAXMEM and 
use dom_mem_op(MEMOP_increase_reservation) to actually reserve memory 
for the new domain. You might want to confirm this by 'bk cset -x'ing 
the changeset -- also, working from that end (the mmap end rather than 
the munmap end) you may have better luck making sense of what is going 
wrong. :-)
 -- Keir


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