Re: dom0 bootstrap for xenstore

[Mike Wray <mike.wray@hp.com>]

Keir Fraser wrote:
> 
> 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.

Isn't it possible to fix xc_map_foreign_range() to do the right thing for
'ordinary' pages?

> 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).

OK, if xc_map_foreign_range() isn't fixable I guess we have to do something
like that.

Mike