xen: fix booting ballooned down hvm guest

xen: fix booting ballooned down hvm guest

commit 5266b8e4445cc836c46689d80a9ff539fa3bfbda upstream.

Commit 96edd61dcf44362d3ef0bed1a5361e0ac7886a63 ("xen/balloon: don't
online new memory initially") introduced a regression when booting a
HVM domain with memory less than mem-max: instead of ballooning down
immediately the system would try to use the memory up to mem-max
resulting in Xen crashing the domain.

For HVM domains the current size will be reflected in Xenstore node
memory/static-max instead of memory/target.

Additionally we have to trigger the ballooning process at once.

Fixes: 96edd61dcf44362d3ef0bed1a5361e0ac7886a63 ("xen/balloon: don't online new memory initially")
Reported-by: Simon Gaiser <hw42@ipsumj.de>
Suggested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>