vfio/pci: Clear VFIO_IRQ_INFO_NORESIZE for MSI-X

Dynamic MSI-X is supported. Clear VFIO_IRQ_INFO_NORESIZE
to provide guidance to user space.
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/fd1ef2bf6ae972da8e2805bc95d5155af5a8fb0a.1683740667.git.reinette.chatre@intel.comSigned-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/pci/vfio_pci_core.c

@@ -1114,7 +1114,7 @@ static int vfio_pci_ioctl_get_irq_info(struct vfio_pci_core_device *vdev,
 	if (info.index == VFIO_PCI_INTX_IRQ_INDEX)
 		info.flags |=
 			(VFIO_IRQ_INFO_MASKABLE | VFIO_IRQ_INFO_AUTOMASKED);
-	else
+	else if (info.index != VFIO_PCI_MSIX_IRQ_INDEX || !vdev->has_dyn_msix)
 		info.flags |= VFIO_IRQ_INFO_NORESIZE;
 
 	return copy_to_user(arg, &info, minsz) ? -EFAULT : 0;

include/uapi/linux/vfio.h

@@ -511,6 +511,9 @@ struct vfio_region_info_cap_nvlink2_lnkspd {
  * then add and unmask vectors, it's up to userspace to make the decision
  * whether to allocate the maximum supported number of vectors or tear
  * down setup and incrementally increase the vectors as each is enabled.
+ * Absence of the NORESIZE flag indicates that vectors can be enabled
+ * and disabled dynamically without impacting other vectors within the
+ * index.
  */
 struct vfio_irq_info {
 	__u32	argsz;