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Re: [Xen-devel] Help? Red Hat fails, Suse/Debian both work fine

On 28 Feb 2006, at 21:45, Magenheimer, Dan (HP Labs Fort Collins) wrote:

We are seeing a strange problem where a recent cset causes
Red Hat to fail domU boot on ia64 complaining of a hotplug
problem but doesn't cause any problem for Suse or Debian.
It is likely some subtle difference (or bug), perhaps in mmap?
Suggestions/advice from anyone more familiar with distro
differences (on ia64) would be appreciated.

Changeset is xen-unstable 8783 ("Use /dev/kmem to map dom0
xenstore page instead of abusing the foreign mapping interface.",
Feb 8, committed by Christian).  Backing out this changeset
or using the small patch below causes the problem to go away,
so we have a workaround, but a root cause would be nice
to know and fix.

Not very many apps use /dev/kmem, and xenstored only uses it once, to map domain0's xenbus page. Can't you just trace the hell out of it and find out exactly what MFN is mapping and why it (presumably) is different from the one allocated by the domain0 kernel for the purpose (the kernel virtual address of which is exported to xenstored via /proc)?

We weren't delighted to end up using /dev/kmem for this purpose, but I don't think our use is an abuse of the interface (I think we're using /dev/kmem mmap() 'within spec' :-).

 -- Keir

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