[PATCH 3/3] VFIO: Direct access config reg without capability

[Gavin Shan <shangw@linux.vnet.ibm.com>]

The config registers in [0, 0x40] is being supported by VFIO. Apart
from that, the other config registers should be coverred by PCI or
PCIe capability. However, there might have some PCI devices (be2net)
who has config registers (0x7c) out of [0, 0x40], and don't have
corresponding PCI or PCIe capability. VFIO will return 0x0 on reading
those registers and writing is dropped. It caused the be2net driver
fails to be loaded because 0x0 returned from its config register 0x7c.

The patch changes the behaviour so that those config registers out
of [0, 0x40] and don't have corresponding PCI or PCIe capability
will be accessed directly.

Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
---
 drivers/vfio/pci/vfio_pci_config.c |   31 ++++++++++++++++++++-----------
 1 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
index 964ff22..5ea3afb 100644
--- a/drivers/vfio/pci/vfio_pci_config.c
+++ b/drivers/vfio/pci/vfio_pci_config.c
@@ -1471,18 +1471,27 @@ static ssize_t vfio_config_do_rw(struct vfio_pci_device *vdev, char __user *buf,
 
 	cap_id = vdev->pci_config_map[*ppos / 4];
 
+	/*
+	 * Some PCI device config registers might not be coverred by
+	 * capability and useful. We will enable direct access to
+	 * those registers.
+	 */
 	if (cap_id == PCI_CAP_ID_INVALID) {
-		if (iswrite)
-			return ret; /* drop */
-
-		/*
-		 * Per PCI spec 3.0, section 6.1, reads from reserved and
-		 * unimplemented registers return 0
-		 */
-		if (copy_to_user(buf, &val, count))
-			return -EFAULT;
-
-		return ret;
+		if (iswrite) {
+			if (copy_from_user(&val, buf, count))
+				return -EFAULT;
+			ret = vfio_user_config_write(vdev->pdev, (int)(*ppos),
+						     val, count);
+			return ret ? ret : count;
+		} else {
+			ret = vfio_user_config_read(vdev->pdev, (int)(*ppos),
+						    &val, count);
+			if (ret)
+				return ret;
+			if (copy_to_user(buf, &val, count))
+				return -EFAULT;
+			return count;
+		}
 	}
 
 	/*
-- 
1.7.5.4