vfio/pci: Probe and store ability to support dynamic MSI-X

Not all MSI-X devices support dynamic MSI-X allocation. Whether
a device supports dynamic MSI-X should be queried using
pci_msix_can_alloc_dyn().

Instead of scattering code with pci_msix_can_alloc_dyn(),
probe this ability once and store it as a property of the
virtual device.

Suggested-by: Alex Williamson <alex.williamson@redhat.com>
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/f1ae022c060ecb7e527f4f53c8ccafe80768da47.1683740667.git.reinette.chatre@intel.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/pci/vfio_pci_core.c

@@ -530,8 +530,11 @@ int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
 		vdev->msix_bar = table & PCI_MSIX_TABLE_BIR;
 		vdev->msix_offset = table & PCI_MSIX_TABLE_OFFSET;
 		vdev->msix_size = ((flags & PCI_MSIX_FLAGS_QSIZE) + 1) * 16;
-	} else
+		vdev->has_dyn_msix = pci_msix_can_alloc_dyn(pdev);
+	} else {
 		vdev->msix_bar = 0xFF;
+		vdev->has_dyn_msix = false;
+	}
 
 	if (!vfio_vga_disabled() && vfio_pci_is_vga(pdev))
 		vdev->has_vga = true;

include/linux/vfio_pci_core.h

@@ -68,6 +68,7 @@ struct vfio_pci_core_device {
 	u16			msix_size;
 	u32			msix_offset;
 	u32			rbar[7];
+	bool			has_dyn_msix:1;
 	bool			pci_2_3:1;
 	bool			virq_disabled:1;
 	bool			reset_works:1;