x86/ioreq server: asynchronously reset outstanding p2m_ioreq_server entries

x86/ioreq server: asynchronously reset outstanding p2m_ioreq_server entries

After an ioreq server has unmapped, the remaining p2m_ioreq_server
entries need to be reset back to p2m_ram_rw. This patch does this
asynchronously with the current p2m_change_entry_type_global()
interface.

New field entry_count is introduced in struct p2m_domain, to record
the number of p2m_ioreq_server p2m page table entries. One nature of
these entries is that they only point to 4K sized page frames, because
all p2m_ioreq_server entries are originated from p2m_ram_rw ones in
p2m_change_type_one(). We do not need to worry about the counting for
2M/1G sized pages.

This patch disallows mapping of an ioreq server, when there's still
p2m_ioreq_server entry left, in case another mapping occurs right after
the current one being unmapped, releases its lock, with p2m table not
synced yet.

This patch also disallows live migration, when there's remaining
p2m_ioreq_server entry in p2m table. The core reason is our current
implementation of p2m_change_entry_type_global() lacks information
to resync p2m_ioreq_server entries correctly if global_logdirty is
on.

We still need to handle other recalculations, however; which means
that when doing a recalculation, if the current type is
p2m_ioreq_server, we check to see if p2m->ioreq.server is valid or
not.  If it is, we leave it as type p2m_ioreq_server; if not, we reset
it to p2m_ram as appropriate.

To avoid code duplication, lift recalc_type() out of p2m-pt.c and use
it for all type recalculations (both in p2m-pt.c and p2m-ept.c).

Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>