Modern virtio PCI is allowed to use both memory and I/O BARs for the
config space, but legacy devices must use I/O for BAR0, as specified by
Virtio v1.0 cs04:
4.1.5.1.1.1 Legacy Interface: A Note on Device Layout Detection
"Transitional devices MUST expose the Legacy Interface in I/O space in
BAR0."
What virtio calls "I/O space" is most certainly port I/O, as hinted by the
discussion in 4.1.4 Virtio Structure PCI Capabilities, where it
distinguishes "memory BARs" from "I/O BARs". This is also the conclusion
made by SeaBIOS [1], which only looks for port I/O in BAR0 when driving a
transitional device.
I think MMIO was made the default by a463650caad6 ("kvm tools: pci: add
MMIO interface to virtio-pci devices") to support ARM targets, but we
support PIO as well as MMIO nowadays. So let's make the legacy virtio
implementation comply with the specification and use port I/O for BAR0.
[1] https://patchwork.kernel.org/patch/10038927/
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>
---
virtio/pci.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/virtio/pci.c b/virtio/pci.c
index 2054c7bac472..9a199013ac49 100644
--- a/virtio/pci.c
+++ b/virtio/pci.c
@@ -450,10 +450,10 @@ int virtio_pci__init(struct kvm *kvm, void *dev, struct virtio_device *vdev,
.class[2] = (class >> 16) & 0xff,
.subsys_vendor_id = cpu_to_le16(PCI_SUBSYSTEM_VENDOR_ID_REDHAT_QUMRANET),
.subsys_id = cpu_to_le16(subsys_id),
- .bar[0] = cpu_to_le32(vpci->mmio_addr
- | PCI_BASE_ADDRESS_SPACE_MEMORY),
- .bar[1] = cpu_to_le32(vpci->port_addr
+ .bar[0] = cpu_to_le32(vpci->port_addr
| PCI_BASE_ADDRESS_SPACE_IO),
+ .bar[1] = cpu_to_le32(vpci->mmio_addr
+ | PCI_BASE_ADDRESS_SPACE_MEMORY),
.bar[2] = cpu_to_le32(vpci->msix_io_block
| PCI_BASE_ADDRESS_SPACE_MEMORY),
.status = cpu_to_le16(PCI_STATUS_CAP_LIST),
--
2.14.3
