[Xen-devel] Re: dom0 bootstrap for xenstore

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 16 Jun 2005, at 09:11, Rusty Russell wrote:

> So here's my patch against latest bk, including test program but we 
> have
> an issue.  On unmap, I hit the BUG_ON() on mm/rmap.c:482.  Is this some
> issue with using xc_map_foreign_range() on non-foreign pages?
Ah, it's not working because xc_map_foreign_range does not raise 
refcnts on the page being mapped. unmap_range then does the right thing 
for foreign pages, and things like the local domain's shared_info page 
which is really a Xen heap page, but will do the wrong thing for 
ordinary pages out of the local domain's page allocator (like the 
xenstored page). It will try to tear down rmap, drop refcnts, atc and 
get itself into a mess.
On XenLinux, /dev/mem and /dev/kmem only work for mapping I/O memory.

Either we need a new interface for mmaping local xenstore page, or we 
need to hack one of the existing /dev/mem or xc_map_foreign_range 
ioctl. None of these options is very pleasant. :-(  I think simplest 
would be to extend the gross /proc/xen/privcmd to have a mmap that we 
can use to mmap xenstore page (maybe make a little more general purpose 
by turning offset field of mmap into an enumeration, so we can map 
other useful Xen-specific bits and bobs via it in the future).
 -- Keir


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