On Mon, May 29, 2023 at 04:07:42PM +0800, Zhu, Lingshan wrote:
>
>
> On 5/29/2023 2:38 PM, Michael S. Tsirkin wrote:
> > On Mon, May 29, 2023 at 02:19:36PM +0800, Zhu, Lingshan wrote:
> > >
> > > On 5/28/2023 7:28 PM, Michael S. Tsirkin wrote:
> > > > On Sat, May 27, 2023 at 02:15:42AM +0800, Zhu Lingshan wrote:
> > > > > Current virtio-net only probes a device with VIRITO_ID_NET == 1.
> > > > >
> > > > > For a modern-transtional virtio-net device which has a transtional
> > > > > device id 0x1000 and acts as a modern device, current virtio-pci
> > > > > modern driver will assign the sub-device-id to its mdev->id.device,
> > > > > which may not be 0x1, this sub-device-id is up to the vendor.
> > > > >
> > > > > That means virtio-net driver doesn't probe a modern-transitonal
> > > > > virtio-net with a sub-device-id other than 0x1, which is a bug.
> > > > No, the bug is in the device. Legacy linux drivers always looked at
> > > > sub device id (other OSes might differ). So it makes no sense
> > > > for a transitional device to have sub-device-id other than 0x1.
> > > > Don't have time to look at spec but I think you will find it there.
> > > That is true for a software emulated transitional device,
> > > because there is only "generation" of instance in the hypervisor,
> > > that allowing it to ensure its sub-device-id always be 0x01,
> > > and it fits VIRTIO_ID_NET.
> > >
> > > However, a vendor may produce multiple generations of transitional
> > > hardware. The sub-device-id is up to the vendor, and it is the
> > > only way to for a driver to identify a device, other IDs are all
> > > fixed as 0x1af4, 0x1000 and 0x8086 for Intel.
> > That is one of the issues with legacy virtio, yes.
> >
> >
> >
> > > So the sub-device-id has to be unique and differ from others, can not always
> > > be 0x01.
> >
> > If you are trying to build a device and want to create a safe way to
> > identify it without breaking legacy drivers, then
> > VIRTIO_PCI_CAP_VENDOR_CFG has been designed for things like this.
> > For example you can have:
> >
> > struct virtio_pci_vndr_data {
> > u8 cap_vndr; /* Generic PCI field: PCI_CAP_ID_VNDR */
> > u8 cap_next; /* Generic PCI field: next ptr. */
> > u8 cap_len; /* Generic PCI field: capability length */
> > u8 cfg_type; /* Identifies the structure. */
> > u16 vendor_id; /* Identifies the vendor-specific format. */
> > u16 device_generation; /* Device generation */
> > };
> This can be a solution for sure.
> >
> > > I propose this fix, all changes are for modern-transitional devices in
> > > modern
> > > code path, not for legacy nor legacy-transitional.
> > >
> > > Thanks
> > But what good is this fix? If you just want the modern driver to bind
> > and ignore legacy just create a modern device, you can play
> > with subsystem id and vendor to your heart's content then.
> Not sure who but there are some use-cases require
> transnational devices than modern devices,
> I don't like this neither.
> >
> > If you are using transitional then presumably you want
> > legacy drives to bind, they will not bind if subsystem device
> > id changes.
> well actually it is a transitional device and act as a
> modern device by default, so modern driver will probe.
>
> I think this fix is common and easy, just let virtio-net
> probe transitional device id 0x1000 just like it probes
> modern device id 0x1. This is a once for all fix.
>
> This fix only affects modern-transitional devices in modern code path,
> legacy is untouched.
>
> Thanks
The point of having transitional as opposed to modern is to allow
legacy drivers. If you don't need legacy just use a non transitional
device.
Your device is out of spec:
Transitional devices MUST have the PCI Subsystem Device ID
matching the Virtio Device ID, as indicated in section \ref{sec:Device Types}.
So you will have to explain why the setup you are describing
makes any sense at all before we consider this a fix.
> >
> >
> > > >
> > > > > Other types of devices also have similar issues, like virito-blk.
> > > > >
> > > > > I propose to fix this problem of modern-transitonal device
> > > > > whith this solution, all in the modern code path:
> > > > > 1) assign the device id to mdev->id.device
> > > > > 2) add transitional device ids in the virtio-net(and others) probe table.
> > > > >
> > > > > Comments are welcome!
> > > > >
> > > > > Thanks!
> > > > >
> > > > > Signed-off-by: Zhu Lingshan <lingshan.zhu@xxxxxxxxx>
> > > > > ---
> > > > > drivers/net/virtio_net.c | 1 +
> > > > > drivers/virtio/virtio_pci_modern_dev.c | 2 +-
> > > > > 2 files changed, 2 insertions(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > > index 56ca1d270304..6b45d8602a6b 100644
> > > > > --- a/drivers/net/virtio_net.c
> > > > > +++ b/drivers/net/virtio_net.c
> > > > > @@ -4250,6 +4250,7 @@ static __maybe_unused int virtnet_restore(struct virtio_device *vdev)
> > > > > static struct virtio_device_id id_table[] = {
> > > > > { VIRTIO_ID_NET, VIRTIO_DEV_ANY_ID },
> > > > > + { VIRTIO_TRANS_ID_NET, VIRTIO_DEV_ANY_ID },
> > > > > { 0 },
> > > > > };
> > > > > diff --git a/drivers/virtio/virtio_pci_modern_dev.c b/drivers/virtio/virtio_pci_modern_dev.c
> > > > > index 869cb46bef96..80846e1195ce 100644
> > > > > --- a/drivers/virtio/virtio_pci_modern_dev.c
> > > > > +++ b/drivers/virtio/virtio_pci_modern_dev.c
> > > > > @@ -229,7 +229,7 @@ int vp_modern_probe(struct virtio_pci_modern_device *mdev)
> > > > > /* Transitional devices: use the PCI subsystem device id as
> > > > > * virtio device id, same as legacy driver always did.
> > > > > */
> > > > > - mdev->id.device = pci_dev->subsystem_device;
> > > > > + mdev->id.device = pci_dev->device;
> > > > > } else {
> > > > > /* Modern devices: simply use PCI device id, but start from 0x1040. */
> > > > > mdev->id.device = pci_dev->device - 0x1040;
> > > > > --
> > > > > 2.39.1
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