On Mon, Mar 19, 2012 at 02:19:33PM -0500, Anthony Liguori wrote:
> On 03/19/2012 10:56 AM, Michael S. Tsirkin wrote:
> >Currently virtio-pci is specified so that configuration of the device is
> >done through a PCI IO space (via BAR 0 of the virtual PCI device).
> >However, Linux guests happen to use ioread/iowrite/iomap primitives
> >for access, and these work uniformly across memory/io BARs.
> >
> >While PCI IO accesses are faster than MMIO on x86 kvm,
> >MMIO might be helpful on other systems which don't
> >implement PIO or where PIO is slower than MMIO.
> >
> >Add a property to make it possible to tweak the BAR type.
> >
> >Signed-off-by: Michael S. Tsirkin<m...@redhat.com>
> >
> >This is harmless by default but causes segfaults in memory.c
> >when enabled. Thus an RFC until I figure out what's wrong.
>
> Doesn't this violate the virtio-pci spec?
>
The point is to change the BAR type depending on the architecture.
IO is fastest on x86 but maybe not on other architectures.
> Making the same vendor/device ID have different semantics depending
> on a magic flag in QEMU seems like a pretty bad idea to me.
>
> Regards,
>
> Anthony Liguori
We do this with MSI-X so why not the BAR type?
> >
> >---
> > hw/virtio-pci.c | 16 ++++++++++++++--
> > hw/virtio-pci.h | 4 ++++
> > 2 files changed, 18 insertions(+), 2 deletions(-)
> >
> >diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> >index 28498ec..6f338d2 100644
> >--- a/hw/virtio-pci.c
> >+++ b/hw/virtio-pci.c
> >@@ -655,6 +655,7 @@ void virtio_init_pci(VirtIOPCIProxy *proxy, VirtIODevice
> >*vdev)
> > {
> > uint8_t *config;
> > uint32_t size;
> >+ uint8_t bar0_type;
> >
> > proxy->vdev = vdev;
> >
> >@@ -684,8 +685,14 @@ void virtio_init_pci(VirtIOPCIProxy *proxy,
> >VirtIODevice *vdev)
> >
> > memory_region_init_io(&proxy->bar,&virtio_pci_config_ops, proxy,
> > "virtio-pci", size);
> >- pci_register_bar(&proxy->pci_dev, 0, PCI_BASE_ADDRESS_SPACE_IO,
> >-&proxy->bar);
> >+
> >+ if (proxy->flags& VIRTIO_PCI_FLAG_USE_MMIO) {
> >+ bar0_type = PCI_BASE_ADDRESS_SPACE_MEMORY;
> >+ } else {
> >+ bar0_type = PCI_BASE_ADDRESS_SPACE_IO;
> >+ }
> >+
> >+ pci_register_bar(&proxy->pci_dev, 0, bar0_type,&proxy->bar);
> >
> > if (!kvm_has_many_ioeventfds()) {
> > proxy->flags&= ~VIRTIO_PCI_FLAG_USE_IOEVENTFD;
> >@@ -823,6 +830,7 @@ static Property virtio_blk_properties[] = {
> > DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
> > VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
> > DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 2),
> > DEFINE_VIRTIO_BLK_FEATURES(VirtIOPCIProxy, host_features),
> >+ DEFINE_PROP_BIT("mmio", VirtIOPCIProxy, flags,
> >VIRTIO_PCI_FLAG_USE_MMIO_BIT, false),
> > DEFINE_PROP_END_OF_LIST(),
> > };
> >
> >@@ -856,6 +864,7 @@ static Property virtio_net_properties[] = {
> > DEFINE_PROP_UINT32("x-txtimer", VirtIOPCIProxy, net.txtimer,
> > TX_TIMER_INTERVAL),
> > DEFINE_PROP_INT32("x-txburst", VirtIOPCIProxy, net.txburst, TX_BURST),
> > DEFINE_PROP_STRING("tx", VirtIOPCIProxy, net.tx),
> >+ DEFINE_PROP_BIT("mmio", VirtIOPCIProxy, flags,
> >VIRTIO_PCI_FLAG_USE_MMIO_BIT, false),
> > DEFINE_PROP_END_OF_LIST(),
> > };
> >
> >@@ -888,6 +897,7 @@ static Property virtio_serial_properties[] = {
> > DEFINE_PROP_HEX32("class", VirtIOPCIProxy, class_code, 0),
> > DEFINE_VIRTIO_COMMON_FEATURES(VirtIOPCIProxy, host_features),
> > DEFINE_PROP_UINT32("max_ports", VirtIOPCIProxy,
> > serial.max_virtserial_ports, 31),
> >+ DEFINE_PROP_BIT("mmio", VirtIOPCIProxy, flags,
> >VIRTIO_PCI_FLAG_USE_MMIO_BIT, false),
> > DEFINE_PROP_END_OF_LIST(),
> > };
> >
> >@@ -915,6 +925,7 @@ static TypeInfo virtio_serial_info = {
> >
> > static Property virtio_balloon_properties[] = {
> > DEFINE_VIRTIO_COMMON_FEATURES(VirtIOPCIProxy, host_features),
> >+ DEFINE_PROP_BIT("mmio", VirtIOPCIProxy, flags,
> >VIRTIO_PCI_FLAG_USE_MMIO_BIT, false),
> > DEFINE_PROP_END_OF_LIST(),
> > };
> >
> >@@ -969,6 +980,7 @@ static int virtio_scsi_exit_pci(PCIDevice *pci_dev)
> > static Property virtio_scsi_properties[] = {
> > DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 2),
> > DEFINE_VIRTIO_SCSI_PROPERTIES(VirtIOPCIProxy, host_features, scsi),
> >+ DEFINE_PROP_BIT("mmio", VirtIOPCIProxy, flags,
> >VIRTIO_PCI_FLAG_USE_MMIO_BIT, false),
> > DEFINE_PROP_END_OF_LIST(),
> > };
> >
> >diff --git a/hw/virtio-pci.h b/hw/virtio-pci.h
> >index e560428..e6a8861 100644
> >--- a/hw/virtio-pci.h
> >+++ b/hw/virtio-pci.h
> >@@ -24,6 +24,10 @@
> > #define VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT 1
> > #define VIRTIO_PCI_FLAG_USE_IOEVENTFD (1<<
> > VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT)
> >
> >+/* Some guests don't support port IO. Use MMIO instead. */
> >+#define VIRTIO_PCI_FLAG_USE_MMIO_BIT 2
> >+#define VIRTIO_PCI_FLAG_USE_MMIO (1<< VIRTIO_PCI_FLAG_USE_MMIO_BIT)
> >+
> > typedef struct {
> > PCIDevice pci_dev;
> > VirtIODevice *vdev;
