@@ -408,6 +408,23 @@ static int vfio_enable_vectors(VFIOPCIDevice *vdev, bool msix)
int ret = 0, i, argsz;
int32_t *fds;
+ /*
+ * If dynamic MSI-X allocation is supported, the vectors to be allocated
+ * and enabled can be scattered. Before kernel enabling MSI-X, setting
+ * nr_vectors causes all these vectors to be allocated on host.
+ *
+ * To keep allocation as needed, use vector 0 with an invalid fd to get
+ * MSI-X enabled first, then set vectors with a potentially sparse set of
+ * eventfds to enable interrupts only when enabled in guest.
+ */
+ if (msix && !vdev->msix->noresize) {
+ ret = vfio_enable_msix_no_vec(vdev);
+
+ if (ret) {
+ return ret;
+ }
+ }
+
argsz = sizeof(*irq_set) + (vdev->nr_vectors * sizeof(*fds));
irq_set = g_malloc0(argsz);
During migration restoring, vfio_enable_vectors() is called to restore enabling MSI-X interrupts for assigned devices. It sets the range from 0 to nr_vectors to kernel to enable MSI-X and the vectors unmasked in guest. During the MSI-X enabling, all the vectors within the range are allocated according to the VFIO_DEVICE_SET_IRQS ioctl. When dynamic MSI-X allocation is supported, we only want the guest unmasked vectors being allocated and enabled. Use vector 0 with an invalid fd to get MSI-X enabled, after that, all the vectors can be allocated in need. Signed-off-by: Jing Liu <jing2.liu@intel.com> --- Changes since RFC v1: - Revise the comments. (Alex) - Call the new helper function in previous patch to enable MSI-X. (Alex) --- hw/vfio/pci.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)