mshv: Ignore second stats page map result failure

mshv: Ignore second stats page map result failure

Older versions of the hypervisor do not have a concept of separate SELF
and PARENT stats areas. In this case, mapping the HV_STATS_AREA_SELF page
is sufficient - it's the only page and it contains all available stats.

Mapping HV_STATS_AREA_PARENT returns HV_STATUS_INVALID_PARAMETER which
currently causes module init to fail on older hypevisor versions.

Detect this case and gracefully fall back to populating
stats_pages[HV_STATS_AREA_PARENT] with the already-mapped SELF page.

Add comments to clarify the behavior, including a clarification of why
this isn't needed for hv_call_map_stats_page2() which always supports
PARENT and SELF areas.

Signed-off-by: Purna Pavan Chandra Aekkaladevi <paekkaladevi@linux.microsoft.com>
Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Reviewed-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Acked-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>