virtiofs: Allow memory hotplug with virtiofs

Kata with virtio-fs fails to do memory hotplugging. This is caused by
the fact that hot plugged memory is always backed by
'memory-backend-ram' while virtio-fs expects it to be backed by file and
shared for it to be able to use the system the way it is intended. This
chnage allows using file based memory backend for virtio-fs, hugepages
or when the user prefers to use a file backed memory

Fixes: kata-containers#1745
Signed-off-by: Ganesh Maharaj Mahalingam <ganesh.mahalingam@intel.com>
(cherry picked from commit d392b22)

virtcontainers/qemu.go

@@ -1355,6 +1355,9 @@ func (q *qemu) hotplugMemory(memDev *memoryDevice, op operation) (int, error) {
 
 func (q *qemu) hotplugAddMemory(memDev *memoryDevice) (int, error) {
 	memoryDevices, err := q.qmpMonitorCh.qmp.ExecQueryMemoryDevices(q.qmpMonitorCh.ctx)
+	share := false
+	target := ""
+	memoryBack := "memory-backend-ram"
 	if err != nil {
 		return 0, fmt.Errorf("failed to query memory devices: %v", err)
 	}
@@ -1368,7 +1371,20 @@ func (q *qemu) hotplugAddMemory(memDev *memoryDevice) (int, error) {
 		}
 		memDev.slot = maxSlot + 1
 	}
-	err = q.qmpMonitorCh.qmp.ExecHotplugMemory(q.qmpMonitorCh.ctx, "memory-backend-ram", "mem"+strconv.Itoa(memDev.slot), "", memDev.sizeMB, false)
+	if q.qemuConfig.Knobs.HugePages {
+		// we are setting all the bits that govmm sets when hugepages are enabled.
+		// https://github.com/intel/govmm/blob/master/qemu/qemu.go#L1677
+		target = "/dev/hugepages"
+		memoryBack = "memory-backend-file"
+		share = true
+	} else if q.config.SharedFS == config.VirtioFS || q.config.FileBackedMemRootDir != "" {
+		target = q.qemuConfig.Memory.Path
+		memoryBack = "memory-backend-file"
+	}
+	if q.qemuConfig.Knobs.FileBackedMemShared {
+		share = true
+	}
+	err = q.qmpMonitorCh.qmp.ExecHotplugMemory(q.qmpMonitorCh.ctx, memoryBack, "mem"+strconv.Itoa(memDev.slot), target, memDev.sizeMB, share)
 	if err != nil {
 		q.Logger().WithError(err).Error("hotplug memory")
 		return 0, err