RE: [Xen-devel] "Iomem mapping not permitted" during windows crash dump under GPLPV

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> 
> Finally, we could just tell James to ignore the warning :), which is
> probably the right answer.

I'm not _that_ fussed about it, but I do like 'xm dmesg' to only tell me
about real problems.

Can Xen tell the difference between a ballooned out page and a missing
page? I suspect it can't but if it could it would allow an easy way to
turn that message off in that case.

> [1] Windows crash dump support is quite peculiar.  It's essentially
> kdump-like, except that the kernel which you kexec appears to have
> been written from scratch for the specific purpose of writing out
> crash dumps and hibernation files, with a compatibility shim so that
> it can run normal Windows drivers.  There's no Microsoft-blessed way
> for normal drivers and dump mode drivers to coordinate, and, while
> there are a few backdoors, they're rather unpleasant; we ended up
> stashing stuff in xenstore.
> 

Reading xenstore at HIGH_LEVEL must be very unpleasant! Do you replicate
the xenstore code in your vbd drivers and poll rather than interrupt at
crash dump time? I map a dummy resources page and store everything
there, which is passed into the crash dump driver so it just picks up
where it left off, and never has to touch xenstore - it just does a very
basic init (picking up the ring pointers etc), cleans up any stale
requests that were submitted before the crash dump and never completed,
then gets to work.

James


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