[PATCH v2] vfio/pci: migration: Skip config space check for vendor specific capability during restore/load

[Vinayak Kale]

In case of migration, during restore operation, qemu checks config space of the
pci device with the config space in the migration stream captured during save
operation. In case of config space data mismatch, restore operation is failed.

config space check is done in function get_pci_config_device(). By default VSC
(vendor-specific-capability) in config space is checked.

Ideally qemu should not check VSC for VFIO-PCI device during restore/load as
qemu is not aware of VSC ABI.

This patch skips the check for VFIO-PCI device by clearing pdev->cmask[] for VSC
offsets. If cmask[] is not set for an offset, then qemu skips config space check
for that offset.

Signed-off-by: Vinayak Kale <vkale@nvidia.com>
---
Version History
v1->v2:
    - Limited scope of change to vfio-pci devices instead of all pci devices.

 hw/vfio/pci.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index d7fe06715c..9edaff4b37 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -2132,6 +2132,22 @@ static void vfio_check_af_flr(VFIOPCIDevice *vdev, 
uint8_t pos)
     }
 }
 
+static int vfio_add_vendor_specific_cap(VFIOPCIDevice *vdev, int pos,
+                                        uint8_t size, Error **errp)
+{
+    PCIDevice *pdev = &vdev->pdev;
+
+    pos = pci_add_capability(pdev, PCI_CAP_ID_VNDR, pos, size, errp);
+    if (pos < 0) {
+        return pos;
+    }
+
+    /* Exempt config space check for VSC during restore/load  */
+    memset(pdev->cmask + pos, 0, size);
+
+    return pos;
+}
+
 static int vfio_add_std_cap(VFIOPCIDevice *vdev, uint8_t pos, Error **errp)
 {
     PCIDevice *pdev = &vdev->pdev;
@@ -2199,6 +2215,9 @@ static int vfio_add_std_cap(VFIOPCIDevice *vdev, uint8_t 
pos, Error **errp)
         vfio_check_af_flr(vdev, pos);
         ret = pci_add_capability(pdev, cap_id, pos, size, errp);
         break;
+    case PCI_CAP_ID_VNDR:
+        ret = vfio_add_vendor_specific_cap(vdev, pos, size, errp);
+        break;
     default:
         ret = pci_add_capability(pdev, cap_id, pos, size, errp);
         break;
-- 
2.34.1