diff options
| -rw-r--r-- | hw/vfio/pci.c | 31 |
1 files changed, 21 insertions, 10 deletions
diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c index f2ba9b6..03a3d01 100644 --- a/hw/vfio/pci.c +++ b/hw/vfio/pci.c @@ -1880,16 +1880,26 @@ static void vfio_add_ext_cap(VFIOPCIDevice *vdev) /* * Extended capabilities are chained with each pointing to the next, so we * can drop anything other than the head of the chain simply by modifying - * the previous next pointer. For the head of the chain, we can modify the - * capability ID to something that cannot match a valid capability. ID - * 0 is reserved for this since absence of capabilities is indicated by - * 0 for the ID, version, AND next pointer. However, pcie_add_capability() - * uses ID 0 as reserved for list management and will incorrectly match and - * assert if we attempt to pre-load the head of the chain with this ID. - * Use ID 0xFFFF temporarily since it is also seems to be reserved in - * part for identifying absence of capabilities in a root complex register - * block. If the ID still exists after adding capabilities, switch back to - * zero. We'll mark this entire first dword as emulated for this purpose. + * the previous next pointer. Seed the head of the chain here such that + * we can simply skip any capabilities we want to drop below, regardless + * of their position in the chain. If this stub capability still exists + * after we add the capabilities we want to expose, update the capability + * ID to zero. Note that we cannot seed with the capability header being + * zero as this conflicts with definition of an absent capability chain + * and prevents capabilities beyond the head of the list from being added. + * By replacing the dummy capability ID with zero after walking the device + * chain, we also transparently mark extended capabilities as absent if + * no capabilities were added. Note that the PCIe spec defines an absence + * of extended capabilities to be determined by a value of zero for the + * capability ID, version, AND next pointer. A non-zero next pointer + * should be sufficient to indicate additional capabilities are present, + * which will occur if we call pcie_add_capability() below. The entire + * first dword is emulated to support this. + * + * NB. The kernel side does similar masking, so be prepared that our + * view of the device may also contain a capability ID zero in the head + * of the chain. Skip it for the same reason that we cannot seed the + * chain with a zero capability. */ pci_set_long(pdev->config + PCI_CONFIG_SPACE_SIZE, PCI_EXT_CAP(0xFFFF, 0, 0)); @@ -1915,6 +1925,7 @@ static void vfio_add_ext_cap(VFIOPCIDevice *vdev) PCI_EXT_CAP_NEXT_MASK); switch (cap_id) { + case 0: /* kernel masked capability */ case PCI_EXT_CAP_ID_SRIOV: /* Read-only VF BARs confuse OVMF */ case PCI_EXT_CAP_ID_ARI: /* XXX Needs next function virtualization */ trace_vfio_add_ext_cap_dropped(vdev->vbasedev.name, cap_id, next); |