vfio/pci: Support 8-byte PCI loads and stores

Many PCI adapters can benefit or even require full 64bit read
and write access to their registers. In order to enable work on
user-space drivers for these devices add two new variations
vfio_pci_core_io{read|write}64 of the existing access methods
when the architecture supports 64-bit ioreads and iowrites.

Signed-off-by: Ben Segal <[e-mail]>
Co-developed-by: Gerd Bayer <[e-mail]>
Signed-off-by: Gerd Bayer <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alex Williamson <[e-mail]>

drivers/vfio/pci/vfio_pci_rdwr.c

···
 VFIO_IOREAD(8)
 VFIO_IOREAD(16)
 VFIO_IOREAD(32)
+#ifdef ioread64
+VFIO_IOREAD(64)
+#endif
 
 #define VFIO_IORDWR(size)						\
 static int vfio_pci_iordwr##size(struct vfio_pci_core_device *vdev,\
···
 VFIO_IORDWR(8)
 VFIO_IORDWR(16)
 VFIO_IORDWR(32)
+#if defined(ioread64) && defined(iowrite64)
+VFIO_IORDWR(64)
+#endif
+
 /*
  * Read or write from an __iomem region (MMIO or I/O port) with an excluded
  * range which is inaccessible.  The excluded range drops writes and fills
···
 		else
 			fillable = 0;
 
+#if defined(ioread64) && defined(iowrite64)
+		if (fillable >= 8 && !(off % 8)) {
+			ret = vfio_pci_iordwr64(vdev, iswrite, test_mem,
+						io, buf, off, &filled);
+			if (ret)
+				return ret;
+
+		} else
+#endif
 		if (fillable >= 4 && !(off % 4)) {
 			ret = vfio_pci_iordwr32(vdev, iswrite, test_mem,
 						io, buf, off, &filled);

include/linux/vfio_pci_core.h

···
 VFIO_IOREAD_DECLATION(8)
 VFIO_IOREAD_DECLATION(16)
 VFIO_IOREAD_DECLATION(32)
+#ifdef ioread64
+VFIO_IOREAD_DECLATION(64)
+#endif
 
 #endif /* VFIO_PCI_CORE_H */