[RFC 10/13] vfio/pci: emulate CXL DVSEC registers in the configuration space

[Zhi Wang <zhiw@nvidia.com>]

A CXL device has many DVSEC registers in the configuration space for
device control and enumeration. E.g. enable CXL.mem/CXL.cahce.

However, the kernel CXL core owns those registers to control the device.
Thus, the VM is forbidden to touch the physical device control registers.

Read/write the CXL DVSEC from/to the virt configuration space.

Signed-off-by: Zhi Wang <zhiw@nvidia.com>
---
 drivers/vfio/pci/vfio_pci_config.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
index 98f3ac2d305c..af8c0997c796 100644
--- a/drivers/vfio/pci/vfio_pci_config.c
+++ b/drivers/vfio/pci/vfio_pci_config.c
@@ -1902,6 +1902,15 @@ static ssize_t vfio_config_do_rw(struct vfio_pci_core_device *vdev, char __user
 
 			perm = &ecap_perms[cap_id];
 			cap_start = vfio_find_cap_start(vdev, *ppos);
+
+			if (cap_id == PCI_EXT_CAP_ID_DVSEC) {
+				u32 dword;
+
+				memcpy(&dword, vdev->vconfig + cap_start + PCI_DVSEC_HEADER1, 4);
+
+				if (PCI_DVSEC_HEADER1_VID(dword) == PCI_VENDOR_ID_CXL)
+					perm = &virt_perms;
+			}
 		} else {
 			WARN_ON(cap_id > PCI_CAP_ID_MAX);
 
-- 
2.34.1