fix #27138800

commit 6e84200c0a2994b991259d19450eee561029bf70 upstream.

This patch adds virtio-pmem driver for KVM guest.

Guest reads the persistent memory range information from
Qemu over VIRTIO and registers it on nvdimm_bus. It also
creates a nd_region object with the persistent memory
range information so that existing 'nvdimm/pmem' driver
can reserve this into system memory map. This way
'virtio-pmem' driver uses existing functionality of pmem
driver to register persistent memory compatible for DAX
capable filesystems.

This also provides function to perform guest flush over
VIRTIO from 'pmem' driver when userspace performs flush
on DAX memory range.
Signed-off-by: NPankaj Gupta <pagupta@redhat.com>
Reviewed-by: NYuval Shaia <yuval.shaia@oracle.com>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>
Acked-by: NJakub Staron <jstaron@google.com>
Tested-by: NJakub Staron <jstaron@google.com>
Reviewed-by: NCornelia Huck <cohuck@redhat.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Reviewed-by: NYang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: NXunlei Pang <xlpang@linux.alibaba.com>