x86/ept: limit calls to memory_type_changed()

x86/ept: limit calls to memory_type_changed()

memory_type_changed() is currently only implemented for Intel EPT, and
results in the invalidation of EMT attributes on all the entries in
the EPT page tables.  Such invalidation causes EPT_MISCONFIG vmexits
when the guest tries to access any gfns for the first time, which
results in the recalculation of the EMT for the accessed page.  The
vmexit and the recalculations are expensive, and as such should be
avoided when possible.

Remove the call to memory_type_changed() from
XEN_DOMCTL_memory_mapping: there are no modifications of the
iomem_caps ranges anymore that could alter the return of
cache_flush_permitted() from that domctl.

Encapsulate calls to memory_type_changed() resulting from changes to
the domain iomem_caps or ioport_caps ranges in the helpers themselves
(io{ports,mem}_{permit,deny}_access()), and add a note in
epte_get_entry_emt() to remind that changes to the logic there likely
need to be propagaed to the IO capabilities helpers.

Note changes to the IO ports or memory ranges are not very common
during guest runtime, but Citrix Hypervisor has an use case for them
related to device passthrough.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>