Re: [PATCH v1] virtio-pci: Fix legacy device flag setting error in probe

[Feng Liu]

On 2023-07-19 p.m.10:27, Jason Wang wrote:
> External email: Use caution opening links or attachments
>
>
> On Wed, Jul 19, 2023 at 11:46 PM Feng Liu <feliu@xxxxxxxxxx> wrote:
> > The 'is_legacy' flag is used to differentiate between legacy vs modern
> > device. Currently, it is based on the value of vp_dev->ldev.ioaddr.
> > However, due to the shared memory of the union between struct
> > virtio_pci_legacy_device and struct virtio_pci_modern_device, when
> > virtio_pci_modern_probe modifies the content of struct
> > virtio_pci_modern_device, it affects the content of struct
> > virtio_pci_legacy_device, and ldev.ioaddr is no longer zero, causing
> > the 'is_legacy' flag to be set as true. To resolve issue, when legacy
> > device is probed, mark 'is_legacy' as true, when modern device is
> > probed, keep 'is_legacy' as false.
> >
> > Fixes: 4f0fc22534e3 ("virtio_pci: Optimize virtio_pci_device structure size")
> > Signed-off-by: Feng Liu <feliu@xxxxxxxxxx>
> > Reviewed-by: Parav Pandit <parav@xxxxxxxxxx>
> > Reviewed-by: Jiri Pirko <jiri@xxxxxxxxxx>
> > ---
> >   drivers/virtio/virtio_pci_common.c | 2 --
> >   drivers/virtio/virtio_pci_legacy.c | 1 +
> >   2 files changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> > index a6c86f916dbd..c2524a7207cf 100644
> > --- a/drivers/virtio/virtio_pci_common.c
> > +++ b/drivers/virtio/virtio_pci_common.c
> > @@ -557,8 +557,6 @@ static int virtio_pci_probe(struct pci_dev *pci_dev,
> >
> >          pci_set_master(pci_dev);
> >
> > -       vp_dev->is_legacy = vp_dev->ldev.ioaddr ? true : false;
> > -
> >          rc = register_virtio_device(&vp_dev->vdev);
> >          reg_dev = vp_dev;
> >          if (rc)
> > diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c
> > index 2257f1b3d8ae..d9cbb02b35a1 100644
> > --- a/drivers/virtio/virtio_pci_legacy.c
> > +++ b/drivers/virtio/virtio_pci_legacy.c
> > @@ -223,6 +223,7 @@ int virtio_pci_legacy_probe(struct virtio_pci_device *vp_dev)
> >          vp_dev->config_vector = vp_config_vector;
> >          vp_dev->setup_vq = setup_vq;
> >          vp_dev->del_vq = del_vq;
> > +       vp_dev->is_legacy = true;
>
> This seems break force_legacy for modern device:
>
>          if (force_legacy) {
>                  rc = virtio_pci_legacy_probe(vp_dev);
>                  /* Also try modern mode if we can't map BAR0 (no IO space). */
>                  if (rc == -ENODEV || rc == -ENOMEM)
>                          rc = virtio_pci_modern_probe(vp_dev);
>
> Thanks

Hi, Jason

In the case of force_legacy, if no IO space occurs, function will return 
directly after vp_legacy_probe, and will not run vp_dev->is_legacy = 
true; because vp_dev is allocated through kzalloc, the default 
vp_dev->is_legacy is false, which It is expected for modern device, so 
it will not break modern device.

What do you think?

int virtio_pci_legacy_probe(struct virtio_pci_device *vp_dev)
{
[...]

	rc = vp_legacy_probe(ldev);
	if (rc)
		return rc;  /* if no IO space, function will return from here */

[...]
	vp_dev->is_legacy = true;
}


> >          return 0;
> >   }
> > --
> > 2.37.1 (Apple Git-137.1)